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Textiles, polymers and composites for buildings


The Textile Institute and Woodhead PublishingThe Textile Institute is a unique organisation in textiles, clothing and footwear. Incorporated in England by a Royal Charter granted in 1925, the Institute has individual and corporate members in over 90 countries. The aim of the Institute is to facilitate learning, recognise achievement, reward excellence and disseminate information within the global textiles, clothing and footwear industries.

Historically, The Textile Institute has published books of interest to its members and the textile industry. To maintain this policy, the Institute has entered into partnership with Woodhead Publishing Limited to ensure that Institute members and the textile industry continue to have access to high calibre titles on textile science and technology.

Most Woodhead titles on textiles are now published in collaboration with The Textile Institute. Through this arrangement, the Institute provides an Editorial Board which advises Woodhead on appropriate titles for future publication and suggests possible editors and authors for these books. Each book published under this arrangement carries the Institute’s logo.

Woodhead books published in collaboration with The Textile Institute are offered to Textile Institute members at a substantial discount. These books, together with those published by The Textile Institute that are still in print, are offered on the Woodhead website at: www.woodheadpublishing.com. Textile Institute books still in print are also available directly from the Institute’s website at: www.textileinstitutebooks.com.

A list of Woodhead books on textile science and technology, most of which have been published in collaboration with The Textile Institute, can be found towards the end of the contents pages.


Woodhead Publishing Series in Textiles: Number 95

Textiles, polymers and composites

for buildings

Edited byGoeran Pohl

Oxford Cambridge Philadelphia New Delhi


Published by Woodhead Publishing Limited in association with The Textile InstituteWoodhead Publishing Limited, Abington Hall, Granta Park, Great AbingtonCambridge CB21 6AH, UKwww.woodheadpublishing.com

Woodhead Publishing, 525 South 4th Street #241, Philadelphia, PA 19147, USA

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First published 2010, Woodhead Publishing Limited© Woodhead Publishing Limited, 2010The authors have asserted their moral rights.

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ISBN 978-1-84569-397-8 (print)ISBN 978-0-84569-999-4 (online)ISSN 2042-0803 Woodhead Publishing Series in Textiles (print)ISSN 2042-0811 Woodhead Publishing Series in Textiles (online)

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Contributor contact details xiiiWoodhead Publishing Series in Textiles xvii

1 Introduction 1G. Pohl, Saarland University of Applied Sciences, Germany1.1 Tall – broad – climate effi cient 21.2 High-tech textiles already infl uence our daily lives 41.3 Features of the constructive formation of buildings

with textiles, fabrics and sheeting 51.4 Building with fi bre-reinforced polymers 61.5 From the fi rst experiences with the application of

fi bre-reinforced polymers up to modern buildings 71.6 Conclusion 9

Part I Main types of textiles and polymers used in building and construction 11

2 Types and production of textiles used for building and construction 13M. Milwich, Insti tute for Textile Technology and Process Engineering Denkendorf (ITV), Germany2.1 Introduction 132. 2 Overview of textile formation technology 292.3 Foils for bu ilding and construction 342.4 Coatings for bu ilding and construction textiles 352.5 Top coats for building and construction 382. 6 Combining optimised materials to form buildtech

composite materials 38

Contents

v

vi Contents


2. 7 Primary structures for building and construction 402. 8 Future trends 41 2 . 9 References and bibliography 48

3 Technical characteristics and requirements of textiles used for building and construction 49B. Baier, University of Duisburg-Essen, Germany3.1 Introduction 493.2 Historical development of fabrics used for

construction 503.3 Overview of textile materials currently used for

construction 553.4 Technical characteristics and requirements of

fabrics for modern structural engineering 623.5 Future trends 663.6 Sources of further information and advice 673.7 References and further reading 67

4 Fibre reinforced polymer composite materials for building and construction 69M. Motavalli, C. Czaderski, A. Schumacher and D. Gsell, Empa, Switzerland 4.1 Introduction 694.2 Constituent materials, material properties and

manufacturing 724.3 Durability of composites 834.4 Fibre reinforced polymer (FRP) composite

materials for strengthening of existing concrete structural members (fl exural, shear, confi nement) 91

4.5 Fibre reinforced polymer (FRP) composite materials for fl exural strengthening 94

4.6 Fibre reinforced polymer (FRP) composite materials for shear strengthening 101

4.7 Fibre reinforced polymer (FRP) composite materials for confi nement 107

4.8 Fibre reinforced polymer (FRP) composite materials for strengthening of existing masonry structures 111

4.9 Fibre reinforced polymer (FRP) composite materials for internal reinforcement 114

4.10 Fibre reinforced polymer (FRP) composite materials for profi les 118

Contents vii


4.11 Future developments 1214.12 References 123

5 Developing and testing textiles and coatings for tensioned membrane structures 129T. Stegmaier, P. Schneider, A. Vohrer and H. Planck, Institute of Textile Technology and Process Engineering Denkendorf (ITV), Germany and R. Blum and H. Bögner-Balz, Laboratorium Blum, Germany5.1 Introduction 1295.2 Material systems used for membranes 1295.3 Test methods and characterization of membranes 1325.4 Mechanical tests and behaviour of membranes 1345.5 Strength of the connecting systems for membranes 1425.6 Transmission of light through membranes 1545.7 Heat and energy transport in membranes 1555.8 Chemical, light and fi re durability of membranes 1725.9 Surface cleaning properties of membranes 1775.10 Overview of commonly used standards for

membranes 1795.11 Future trends: methods of improving membrane

properties 1795.12 Sources of further information and advice 1855.13 Bibliography 188

6 Polymer foils used in construction 189L. Schiemann, Mayr | Ludescher | Partner, Germany and K. Moritz, seele cover GmbH, Germany6.1 Introduction 1896.2 Construction methods and types of ETFE-foil

structures 1906.3 Historical development: signifi cant ETFE projects 1936.4 Typology, basic shapes and range of application 2036.5 ETFE-foils – morphology and production

progress 2056.6 Material properties 2106.7 Load-bearing behaviour of ETFE-foil structures 2156.8 Development potential of ETFE-foils in

architecture 2196.9 Future requirements for architecture and civil

engineering 2206.10 References 2236.11 Appendix 223

viii Contents


Part II Applications of textiles and polymers in construction 227

7 Tensile structures – textiles for architecture and design 229J. Chilton, Nottingham Trent University, UK7.1 Introduction 2297.2 Brief history and development of tensile structures 2307.3 Concept of fabric architecture 2317.4 General principles of tensile structures 2317.5 Design development – form-fi nding, patterning

and pre-stress 2337.6 Common materials and their architectural

properties 2407.7 Applications and examples of tensile structures 2447.8 Future trends 2527.9 Sources of further information and advice 2547.10 References 255

8 The role, properties and applications of textile materials in sustainable buildings 258J. Pohl, Lightweight Constructions Institute, Germany and G. Pohl, Saarland University of Applied Sciences, Germany8.1 Introduction 2588.2 The role of textile materials in sustainable

buildings 2598.3 Applications and properties of textiles used for

roofi ng and facades of sustainable building concepts 260

8.4 Future trends 2878.5 Sources of further information and advice 2878.6 References and bibliography 288

9 Learning from nature: lightweight constructions using the ‘technical plant stem’ 290M. Milwich, Institute for Textile Technology and Process Engineering Denkendorf (ITV), Germany and T. Speck, Universität Freiburg, Germany9.1 Introduction 2909.2 Using biomimetics to enhance the lightweight

potential of composites 2919.3 Exploiting plant role models for technical use 2959.4 Production of the ‘technical plant stem’ 302

Contents ix


9.5 Applications of the ‘technical plant stem’ 3049.6 Future trends 3079.7 References 308

10 The role of textiles in providing biomimetic solutions for construction 310G. Pohl, Saarland University of Applied Sciences, Germany, T. Speck and O. Speck, Universität Freiburg, Germany and J. Pohl, Lightweight Constructions Institute, Germany10.1 Introduction 31010.2 Defi nitions of biomimetics, bionics and technical

biology 31110.3 Benefi ts of natural developments for technical

purposes 31210.4 Methodology of biomimetics in architecture and

engineering 31210.5 Applications of biomimetics in architecture 31810.6 Future trends 32110.7 Sources of further information and advice 32610.8 References 327

11 Smart textile and polymer fi bres for structural health monitoring 330A. Güemes, Universidad Politecnica de Madrid, Spain and T. B. Messervey, D’Appolonia S.p.A., Italy11.1 Introduction: concept of structural health

monitoring (SHM) 33011.2 Smart fi bres for structural health monitoring

(SHM) 33311.3 Smart composites 34011.4 Future trends 34411.5 Smart textiles 34611.6 Sources of further information and advice 34911.7 References 350

12 Textiles for insulation systems, control of solar gains and thermal losses and solar systems 351J. M. Cremers, Hochschule für Technik (HFT) Stuttgart, Germany and Hightex GmbH, Rimsting, Germany12.1 Introduction 35112.2 Heat protection for membranes: fl exible translucent

thermal insulation 352

x Contents


12.3 Selective and low-E functional coatings for membrane materials (PTFE/ETFE) 358

12.4 Fully membrane-integrated photovoltaics: PV fl exibles (PTFE/ETFE) 364

12.5 Conclusion 37312.6 References 374

13 Sustainable buildings: biomimicry and textile applications 375E. Hertzsch, University of Melbourne, Australia13.1 Introduction 37513.2 Implementation of textile materials in Australia 37713.3 Strategies for facades to reduce the operational

energy demand 37913.4 Contributions of textile materials to reduce the

operational energy demand, and comparisons with examples from nature 381

13.5 Deliberations on future applications 39213.6 References 39513.7 Appendix 396

14 Challenges in using textile materials in architecture: the case of Australia 398E. Hertzsch and K. Lau, University of Melbourne, Australia14.1 Introduction 39814.2 Aim, objectives and methodology of the study 39914.3 Results of the interview 40014.4 Summary of results 41614.5 Conclusions and deliberations on future

developments 41714.6 References 418

15 Innovative composite-fi bre components in architecture 420G. Pohl, Saarland University of Applied Sciences, Germany and M. Pfalz, FIBER-TECH Products GmbH, Germany15.1 Introduction 42015.2 Historical backgroud 42115.3 Materials for composites 42315.4 Design and manufacture of composites for

buildings 431

Contents xi


15.5 Composites in building: the ‘Space Offi ce’ prototype 436

15.6 Composites in buildings: The Walbrook, London 442

15.7 Composites in buildings: The Feathered Wing, Feuchtwangen, Germany 460

15.8 Acknowledgements 46715.9 Bibliography 469

Index 471


Contributor contact details

(* = main contact)

Chapter 1

G. PohlSaarland University of Applied

SciencesSchool of Architecture and

EngineeringWaldhausweg 1466123 SaarbrückenGermanyE-mail: [email protected]

Chapter 2

M. MilwichInstitute for Textile Technology

and Process Engineering Denkendorf (ITV)

Körschtalstrasse 2673770 DenkendorfGermanyE-mail: markus.milwich@

itv-denkendorf.de

Chapter 3

B. BaierUniversity of Duisburg-EssenUniversitätsstrasse 1545141 EssenGermanyE-mail: [email protected]@online.de

Chapter 4

M. Motavalli*, C. Czaderski, A. Schumacher and D. Gsell

EmpaSwiss Federal Laboratories for

Materials Science and Technology

Ueberland-Strasse 1298600 DuebendorfSwitzerlandE-mail: Masoud.Motavalli@

empa.ch

xiii

xiv Contributor contact details


Chapter 5

T. Stegmaier*, P. Schneider, A. Vohrer and H. Planck

Institute of Textile Technology and Process Engineering Denkendorf (ITV)

Körschtalstrasse 2673770 DenkendorfGermanyE-mail: Thomas.stegmaier@

itv-denkendorf.de

R. Blum and H. Bögner-BalzLaboratorium BlumHandwerkstrasse 5870565 Stuttgart-VaihingenGermanyE-mail: [email protected]

Chapter 6

L. Schiemann*Mayr | Ludescher | Partner –

Consulting EngineersHohenzollernstrasse 8980796 MunichGermanyandTechnische Universität MünchenFaculty of ArchitectureInstitute of Structural DesignArcisstrasse 2180333 MünchenGermanyE-mail: [email protected]@mayr-ludescher.de

K. Moritzseele cover GmbHBahnhofstrasse 2883119 ObingGermanyE-mail: [email protected]

Chapter 7

J. ChiltonSchool of Architecture, Design and

Built EnvironmentNottingham Trent UniversityBurton StreetNottingham NG1 4BUUKE-mail: [email protected]

Chapter 8

J. Pohl*Lightweight Constructions InstituteBerggasse 107745 JenaGermanyE-mail: [email protected]


Sciences School of Architecture and Engineering

Waldhausweg 1466123 SaarbrückenGermanyE-mail: [email protected]

Chapter 9

M. Milwich*Institute for Textile Technology

and Process Engineering Denkendorf (ITV)

Körschtalstrasse 2673770 DenkendorfGermanyE-mail: markus.milwich@itv-

denkendorf.de

Contributor contact details xv


T. SpeckUniversität FreiburgInstitut für Biologie IISchänzlestrasse 179104 FreiburgGermanyE-mail: thomas.speck@biologie.

uni-freiburg.de

Chapter 10

G. Pohl*Saarland University of Applied



T. Speck and O. SpeckUniversität FreiburgInstitut für Biologie IISchänzlestrasse 179104 FreiburgGermanyE-mail: thomas.speck@biologie.

[email protected].

de

J. PohlLightweight Constructions InstituteBerggasse 107745 JenaGermanyE-mail: [email protected]

Chapter 11

A. Güemes*Department of AeronauticsUniversidad Politecnica de MadridPlaza Cardenal Cisneros, 328040 MadridSpainE-mail: [email protected]

T. B. MesserveyInnovation and Research DivisionD’Appolonia S.p.A.Via San Nazaro, 1916145 GenovaItalyE-mail: thomas.messervey@

dappolonia.it

Chapter 12

J. M. CremersBuilding Technology and

Integrated ArchitectureHochschule für Technik (HFT)

StuttgartFaculty of Architecture and DesignSchellingstrasse 2470174 StuttgartGermany

and

Hightex GmbHNordstrasse 1083253 Rimsting/ChiemseeGermanyE-mail: [email protected]@hightexworld.com

xvi Contributor contact details


Chapter 13

E. HertzschUniversity of MelbourneFaculty of Architecture, Building

and Planning3010 ParkvilleMelbourneVictoriaAustraliaE-mail: [email protected]

Chapter 14

E. Hertzsch*Faculty of Architecture, Building

and PlanningThe University of Melbourne3010 ParkvilleMelbourneVictoriaAustraliaE-mail: [email protected]

K. LauFaculty of Architecture, Building

and PlanningThe University of Melbourne3010 ParkvilleMelbourneVictoriaAustraliaE-mail: [email protected]

Chapter 15




M. PfalzFIBER-TECH Products GmbHTuchschererstrasse 1009116 ChemnitzGermanyE-mail: info@fi ber-tech.de


Woodhead Publishing Series in Textiles

1 Watson’s textile design and colour Seventh edition Edited by Z. Grosicki

2 Watson’s advanced textile design Edited by Z. Grosicki

3 Weaving Second edition P. R. Lord and M. H. Mohamed

4 Handbook of textile fi bres Vol 1: Natural fi bres J. Gordon Cook

5 Handbook of textile fi bres Vol 2: Man-made fi bres J. Gordon Cook

6 Recycling textile and plastic waste Edited by A. R. Horrocks

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8 Atlas of fi bre fracture and damage to textiles Second edition J. W. S. Hearle, B. Lomas and W. D. Cooke

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10 Physical testing of textiles B. P. Saville

11 Geometric symmetry in patterns and tilings C. E. Horne

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13 Textiles in automotive engineering W. Fung and J. M. Hardcastle

xvii

xviii Woodhead Publishing Series in Textiles


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25 Wool: Science and technology Edited by W. S. Simpson and G. Crawshaw

26 Dictionary of textile fi nishing H-K. Rouette

27 Environmental impact of textiles K. Slater

28 Handbook of yarn production P. R. Lord

29 Textile processing with enzymes Edited by A. Cavaco-Paulo and G. Gübitz

30 The China and Hong Kong denim industry Y. Li, L. Yao and K. W. Yeung

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32 Chemical fi nishing of textiles W. D. Schindler and P. J. Hauser

Woodhead Publishing Series in Textiles xix


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36 Synthetic fi bres: nylon, polyester, acrylic, polyolefi n Edited by J. E. McIntyre

37 Woollen and worsted woven fabric design E. G. Gilligan

38 Analytical electrochemistry in textiles P. Westbroek, G. Priniotakis and P. Kiekens

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40 Chemical testing of textiles Edited by Q. Fan

41 Design and manufacture of textile composites Edited by A. C. Long

42 Effect of mechanical and physical properties on fabric hand Edited by Hassan M. Behery

43 New millennium fi bers T. Hongu, M. Takigami and G. O. Phillips

44 Textiles for protection Edited by R. A. Scott

45 Textiles in sport Edited by R. Shishoo

46 Wearable electronics and photonics Edited by X. M. Tao

47 Biodegradable and sustainable fi bres Edited by R. S. Blackburn

48 Medical textiles and biomaterials for healthcare Edited by S. C. Anand, M. Miraftab, S. Rajendran and J. F. Kennedy

49 Total colour management in textiles Edited by J. Xin

50 Recycling in textiles Edited by Y. Wang

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xx Woodhead Publishing Series in Textiles


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56 Thermal and moisture transport in fi brous materials Edited by N. Pan and P. Gibson

57 Geosynthetics in civil engineering Edited by R. W. Sarsby

58 Handbook of nonwovens Edited by S. Russell

59 Cotton: Science and technology Edited by S. Gordon and Y-L. Hsieh

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64 Sizing in clothing Edited by S. Ashdown

65 Shape memory polymers and textiles J. Hu

66 Environmental aspects of textile dyeing Edited by R. Christie

67 Nanofi bers and nanotechnology in textiles Edited by P. Brown and K. Stevens

68 Physical properties of textile fi bres Fourth edition W. E. Morton and J. W. S. Hearle

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Woodhead Publishing Series in Textiles xxi


71 Polyesters and polyamides Edited by B. L. Deopura, R. Alagirusamy, M. Joshi and B. S. Gupta

72 Advances in wool technology Edited by N. A. G. Johnson and I. Russell

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74 3D fi brous assemblies: Properties, applications and modelling of three-dimensional textile structures

J. Hu

75 Medical and healthcare textiles Edited by S. C. Anand, J. F. Kennedy, M. Miraftab and S. Rajendran

76 Fabric testing Edited by J. Hu

77 Biologically inspired textiles Edited by A. Abbott and M. Ellison

78 Friction in textile materials Edited by B. S. Gupta

79 Textile advances in the automotive industry Edited by R. Shishoo

80 Structure and mechanics of textile fi bre assemblies Edited by P. Schwar t z

81 Engineering textiles: Integrating the design and manufacture of textile products

Edited by Y. E. El-Mogahzy

82 Polyolefi n fi bres: Industrial and medical applications Edited by S. C. O. Ugbolue

83 Smart clothes and wearable technology Edited by J. McCann and D. Bryson

84 Identifi cation of textile fi bres Edited by M. Houck

85 Advanced textiles for wound care Edited by S. Rajendran

86 Fatigue failure of textile fi bres Edited by M. Miraftab

87 Advances in carpet technology Edited by K. Goswami

88 Handbook of textile fi bre structure Volume 1 and Volume 2 Edited by S. J. Eichhorn, J. W. S. Hearle, M. Jaffe and T. Kikutani

xxii Woodhead Publishing Series in Textiles


89 Advances in knitting technology Edited by K-F. Au

90 Smart textile coatings and laminates Edited by W. C. Smith

91 Handbook of tensile properties of textile and technical fi bres Edited by A. R. Bunsell

92 Interior textiles: Design and developments Edited by T. Rowe

93 Textiles for cold weather apparel Edited by J. T. Williams

94 Modelling and predicting textile behaviour Edited by X. Chen

95 Textiles, polymers and composites for buildings Edited by G. Pohl

96 Engineering apparel fabrics and garments J. Fan and L. Hunter

97 Surface modifi cation of textiles Edited by Q. Wei

98 Sustainable textiles Edited by R. S. Blackburn

99 Advances in yarn spinning technology Edited by C. A. Lawrence

100 Handbook of medical textiles Edited by V. T. Bartels

101 Technical textile yarns Edited by R. Alagirusamy and A. Das

102 Applications of nonwovens in technical textiles Edited by R. A. Chapman

103 Colour measurement: Principles, advances and industrial applications Edited by M. L. Gulrajani

104 Textiles for civil engineering Edited by R. Fangueiro

105 New product development in textiles Edited by B. Mills

106 Improving comfort in clothing Edited by G. Song

107 Textile biotechnology Edited by V. A. Nierstrasz and A. Cavaco-Paulo

Woodhead Publishing Series in Textiles xxiii


108 Textiles for hygiene and infection control Edited by B. McCarthy

109 Nanofunctional textiles Edited by Y. Li

110 Joining textiles: Principles and applications Edited by I. Jones and G. Stylios

111 Soft computing in textile engineering Edited by A. Majumdar

112 Textile design Edited by A. Briggs-Goode and K. Townsend

113 Biotextiles as medical implants Edited by M. King and B. Gupta

114 Textile thermal bioengineering Edited by Y. Li

115 Woven textile structure B. K. Behera and P. K. Hari

116 Handbook of textile and industrial dyeing Volume 1: Principles processes and types of dyes

Edited by M. Clark

117 Handbook of textile and industrial dyeing Volume 2: Applications of dyes Edited by M. Clark

118 Handbook of natural fi bres Volume 1: Types, properties and factors affecting breeding and cultivation

Edited by R. Kozlowski

119 Handbook of natural fi bres Volume 2: Processing and applications Edited by R. Kozlowski

120 Functional textiles for improved performance, protection and health Edited by N. Pan and G. Sun

121 Computer technology for textiles and apparel Edited by Jinlian Hu

122 Advances in military textiles and personal equipment Edited by E. Sparks

123 Specialist yarn, woven and fabric structure: Developments and applications Edited by R. H. Gong


1

1Introduction

G. POHL, Saarland University of Applied Sciences, Germany

At the 2008 Olympic Games in Beijing, a ‘Bird’s Nest’ of an arena served as the symbol and the expression of the entitlement to prestige which growing industrial nations are prone to displaying. This sports centre and the ‘bubbling’ Olympic swimming pools as neighbouring buildings remain fi xed in the memory because of their chameleon-like vibrancy due to the light and transparent sheathing. In 2010, the Soccer City Stadium in Johannesburg, the Moses Mabhida Stadium in Durban and the Nelson Mandela Bay Stadium in Port Elisabeth became icons of the fi rst football World Cup ever held on the African continent. Sheathing constructions, composed of light fabrics and polymer sheeting, have become a tool of modern architecture implemented not only as a multifaceted marketing instrument, but also as a kind of highly effi cient large-scale protective suit for people. The utopia as envisioned by Richard Buckminster Fuller in the 1950s and Frei Otto in the 1960s and 1970s that called for the stretching of skins over cities like Manhattan or villages in the Antarctic, seem to have found themselves a reality when one looks at the projects mentioned above. Even though the specifi ed covering distance of 2 miles has not (yet) been achieved, the materials for such projects are long since on the advance: in addition to steel, applications of textiles and polymers are playing a more and more important role for innovative projects.

Fritz Lang’s fi lm ‘Metropolis’, which premiered in 1927 in Berlin and was thought lost until rediscovered in 1958 in Parisian archives, shows a utopian city with skyscrapers connected to each other via bridges, and aeroplanes that fl y between the buildings through endless chasms seeming to be thousands of Grand Canyons. ‘Metropolis’ takes place in the year 2026 at a time when the population is split between workers who must live and die in the dark underground and the elite who enjoy a futuristic city of splendour. Had the fi lm-maker been able to imagine the possibilities of textiles, fabrics, polymer sheeting, fi bre composites or reinforced concrete for his constructions, then he would likely have presented a real utopian utopia. The upper world would have been completely distanced from stony

��

2 Textiles, polymers and composites for buildings


high-rise buildings, resulting in lightweight climate-bubbles, transparent interiors and exteriors, traversable or simply visible public or private green spaces which would have resulted in a multi-layered cellular organism, which when covered by Buckminster Fuller’s dome, would be ready for self-suffi cient space travel.

1.1 Tall – broad – climate effi cient

From the idea of cellular climatic spaces in favour of a ‘futuristic city of splendour’, the possibility of implementation with present-day materials – which defi nes the constructive realisation – is not far off. Projects that eclipse even Fritz Lang’s ‘Metropolis’ constructions are springing up like mushrooms: at a height of 321.25 m, the luxury hotel in Dubai Burj al-Arab is much lower than the tallest building – Burj Khalifa at 828 m – but its 14,000 m2 textile membrane serves to create climatised interior spaces. As a replacement for glass and instead of massive walls, here and in many other examples, such skins have become market-ready and available in a wide range of materials for various applications. The reason for the run on climate skins is a logical one: it is based upon the wish for the creation of an energy-effi cient total concept that usually results in an onion-like sequence of multiple functional layers with a fi nal outer shell that is able to acquire energy. City planning is also beginning to take on this tenor to the extent that textiles, polymers and lightweight constructive elements are fi nding broader application. An example of this is the planning undertaken by Norman Foster’s offi ce for Masdar City in Abu Dhabi. The centre of this green city in the middle of the desert, Masdar Plaza, is covered by screens. These screens cast shadows on the ground during the daytime and become lit steles at night. During the day they convert sunlight into energy, in order to use the stored energy for lighting the evenings and turning the plaza into a luminous paradise. Furthermore, the screens enhance the cooling shadow effect because of their surface treatment with a refl ective low-emissivity coating that reduces the long-wavelength radiation. Such surface treatments of textile materials have been successfully tested in projects such as the canopy above the boarding gates at the airport in Bangkok and are now in the phase of further technical and industrial development.

Screen constructions such as those in Masdar Plaza are defi nitely not an invention of contemporary times. Even before primeval times, humans were using screens to protect themselves from the sun or rain. Although the amphitheatres of the Roman Empire were created with broad lengths of fabric as fl exible sunshades, it is only now that complex, sophisticated, mechanical constructions for lightweight superstructures and facades are possible. The seemingly fl oating structure built by Frei Otto in 1955 for the

��

Introduction 3


German National Garden Exhibition in Kassel as a temporary pillow-construction, and his delicate foldable screens for Pink Floyd concerts, are just a few examples in a series of countless developments of modern light-weight construction methods. As a result of the complexity that lies at the heart of this technology, not only structural engineers and architects concern themselves with these screens, but also physicists and other specialists in energy-effi cient technologies. These industrially developed materials are being used in fully new ways: with the protection from sun and rain, it is important to unify the complexity of all necessary functions in one compos-ite material. Furthermore, with facades, both low heat transfer and energy acquisition are usually required. The reduction of energy radiation exchange with the night sky should limit the ability of the building to cool off and similarly protect the building from overheating during the day – all of which can be achieved with fabrics.

Simple developments for the refl ection of sunlight or the nightly back-refl ection of interior warmth are things that have long been in use by greenhouses. For this application, lightweight fabrics are used, which are woven with the addition of aluminium strips. According to the density of the parallel-ordered aluminium threads, the permeability of the fabric for light and air can be varied – low emittance with low tech. The negative aspect of limited mechanical resilience and limited refractoriness is almost a non-issue with greenhouses, but buildings that are created to house larger numbers of people require more robust fabrics. Such fabrics are also avail-able today: at the speed-skating rink for 2011 fi nalised by Behnisch archi-tects and Pohl architects in Inzell, Germany, textile membranes with integrated fi bres with low-emittance qualities are the constituent elements of an active-energy roof construction. The fabric functions as climatic shield, light refl ector, sound insulation, fi re protection, spatial closure and optical functionary.

Contemporary developments of construction technology have, with the help of textile elements, come to the point where massive construction methods succeed to a much lesser degree: in the assembly of materials with multiple characteristics and the formation of a new architectonic language of expression. The implementation of structural utopia in the age of genera-tive design using scripting technologies is a great challenge for manufactur-ing, detailed construction and application of materials. The industry is not attuned to BLOB (Binary Large Objects) architecture. It is characterised by heavy materials, laying of stone upon stone, integration of normed steel profi les and manual assembly. The role of the tradesman in industrial society has been fundamentally oriented to the assembly of semi-fi nished components, which naturally leaves no space for individual material opti-misations. This is quite different from the working method of the sail-maker, for example: semi-fi nished components are also used, namely fabrics

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and foils, but these are combined for an individual sail appropriate for the respective boat. This can also be found in the fi rst tent-construction com-panies from Stromeyer and Bird, where buildings were crafted from indi-vidually cut and sewn or glued lengths of fabric. Today, the industry offers fabric composites that not only protect the bearing fi bres but also have a layer to repel dirt and additional materials that have characteristics that we know from nature: bearing, covering, protecting, energy harvesting, attract-ing, transpiring, etc. For facade construction in the future, insulation and semi-permeability will be assigned the same high priorities as are offered by the breathable high-performance textiles in jackets and coats.

1.2 High-tech textiles already infl uence our daily lives

High-tech functional textiles for clothing have replaced cotton and leather. Most motorcyclists no longer wear leathers, which are heavy, too hot in summer and not effi ciently waterproof, but rather have decided to wear much lighter protective clothing made from artifi cial materials, which in addition to a greater abrasion resistance are also well insulated against heat and cold, are waterproof and still have a good degree of permeability from within to outside. Protective clothing for the workplace is put under daily long-term strain. Special textiles prevent gases, poisons and chemicals from penetrating clothing. Gloves made from textiles with special fi bres are soft inside and cut-resistant on the outside. This is not to imply that artifi cial fi bres are better than natural fi bres, for example high-performance poly-ethylene, also known by its market trade name Dyneema, is entwined with coconut thread: high-tech meets nature – the result is a hybrid composite thread that offers effi cient protection from cuts and is used in safety gloves. The skin comes in contact with soft bamboo thread. Multiple-layered tex-tiles in these gloves even keep out chlorine, ammonia and hydrocarbons.

Materials that can change their state are also being applied. Phase chang-ing materials (PCMs) are applied in the construction industry with the help of encapsulated paraffi n balls that are microscopically small – primarily in walls and ceiling elements. Some current building concepts with high inte-rior climatic demands are also using PCMs. For textiles there are also developments where PCM components have been introduced into special mesh. The mesh creates a type of insulation, can absorb warmth and change its structure, and when it is cold it can release this warmth. This material has been developed as protective clothing for the workers on offshore drill-ing platforms; it keeps them cool during their transit by helicopter and can keep them warm for a long time should the craft be ditched. For buildings such applications remain to be applied.

Conductive fabrics are used not only in the textile industry but also as carbon fi bre heating (CFP) moulds in the construction of fi bre-reinforced

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Introduction 5


polymers. In the textile industry, it is possible to include electrically conduc-tive structures in the fabrics. They can be used to transmit energy or infor-mation, or even for the integration of electrical components. The advantage of the threads is that, as opposed to metallic fi laments, they possess a degree of fl exibility that does not negatively impact the conductivity of the threads. For the construction industry, ‘intelligent’ facades could be highly func-tional: facades that light up and also can absorb energy, photovoltaic facades, or facades that can deliver information or even function as medial facades. Complete circuits can be integrated, and heating facades can be created out of textiles. Light-emitting diodes (LEDs) can also be introduced into the textiles: surface mounted device (SMD)-LEDs are 1.6 mm long and can be used for advertising or lighting. Examples from the clothing industry and special materials show that innovative applications in architecture are at the nascent stages. With technical mass-production, such qualities as men-tioned above can even be cost-effi ciently produced and applied.

1.3 Features of the constructive formation of

buildings with textiles, fabrics and sheeting

In most building applications, textile membranes are used in the form of laminated textiles. They are stabilised, in that they were mechanically or geometrically pre-stressed. Geometric pre-stressing can by synclastic (‘like a bowl’) or anticlastic (‘like a saddle’). Purely mechanical tensioning can take place in almost a fl at plane, e.g. for advertising banners. Textile con-structions require permanent tensioning, which is why such forms can be distinguished in that they create three-dimensional sweeps, have supporting elements (rods or bows), or utilise pneumatic pressure. The most common applications of fabric membranes use polyvinyl chloride (PVC)-coated polyester fabric and polytetrafl uoroethylene (PTFE)-coated fi breglass fabric or fi breglass fabric with a silicon coating. The fabrics are usually made of warped or wefted threads in the long or cross directions and usually act anisotropically, which is to say that they display differing stiffnesses in respective directions. In coated fabrics, the durable fi bres transfer the load, whereas the coating protects the fabric from environmental impacts, is responsible for the impermeability and dictates the level of transparency.

Sheeting is usually applied as ethylene tetrafl uoroethylene (ETFE), which is a material that has no additional components. Meanwhile, sheeting is often combined with fi breglass belts or the sheeting is supported with steel cable. Sheeting is usually highly translucent and readily recyclable. The application usually dictates pneumatic constructions, which are com-posed of two, three or more layers of sheeting and use internal pressure to achieve the sheeting sweep and to provide stabilisation, assuming that the sheeting is stretched in a frame.

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Roofs spanning great distances are often realised with textile membranes and sheeting in the most common lightweight-construction buildings. The primary load-bearing constructions are usually of steel or wood; however, in pneumatic structures this can be achieved with cell-like constructive ele-ments or through the high interior air pressure of the well-known system of air-supported domes, although not with the same load-bearing capacity. Depending upon the type of fabric and coating, fabric membranes are appropriate for convertible constructions and can be used as facade materi-als or even for roofi ng. As a climate hull, fabric membranes are applied in multiple layers; pneumatic pillow-sheeting constructions can achieve insu-lation values with three layers that enable the creation of thermally unprob-lematic spaces. The inclusion of photovoltaic modules is still not suffi ciently advanced, since the modules that are separate, fl exible sheeting elements must be mounted onto the membranes and possess different distortion coeffi cients from the bearing membrane, and from a design perspective are still not found to be satisfactory. The production of fabrics with integrated photovoltaic threads is highly desirable, as is the crossover of qualities common to high-tech textiles from the clothing industry to that of the build-ing industry.

1.4 Building with fi bre-reinforced polymers

Building with fi bres is a fi eld that uses composite materials composed of fi bres that are embedded in a polymer matrix. In aeronautics, in the aero-space industry and for high-performance yacht construction, application of fi bre-reinforced polymers is no longer to be dismissed. Formula 1 racing cars are lighter and more physically stable due to the application of carbon fi bre components. Developments in the USA at the end of the 1930s led to unsaturated polyester resin, composed of long-chain molecules that, due to their chemically unsaturated structure and their availability in dis-solved form as a reactive fl uid resin, were the fi rst matrix used in the application of fi bre-reinforced polymers. Quite early, the already known fi breglass was introduced to the polymer matrix, which resulted in a great improvement of the mechanical durability of the hardened product. Usually such fi bre-composite constructions fi nd their application in the form of constructive elements in a shell composed of multiple layers. Polymer shell elements made of fi bre-reinforced polymers are usually constructed from an upper and a lower shell, with a three-dimensional core material inserted between, which are then glued together and create a closed and very stiff torsional box. This construction method with fi bre-reinforced polymers allows for the arrangement of the fi bres within the individual elements according to the main directions of load transfer, which in turn allows for the optimisation of the elements from a structural perspective

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Introduction 7


towards effectiveness in material consumption and high load-bearing performance.

Through economical serial construction, thin-walled and lightweight ele-ments are created. Lower weight not only saves expenditure in terms of the lower-dimensioned substructure necessary for bearing the load, but also helps to minimise usage of the expensive materials necessary for fi bre-reinforced polymers. From a structural perspective, thin shells rapidly deform under small loads, which can be avoided through sweeps, folds or the application of sandwich construction techniques. Sandwich construction involves fi lling the inside of the shell with foam, paper or metal honeycomb or, in the construction of yachts, with balsa wood. Most shells are formed so that on the inside only membrane forces are acting and bending moments cannot occur. Shells and folded plates can effectively circumvent buckling. Advantages of this construction method are the reduction of the number of construction elements due to integral construction techniques, the high degree of reproducibility and form-exactness, great fl exibility, surface dura-bility and stability. In the ‘Tournesol’ swimming baths in France, the wall-element panels of the interior structures were formed as trays, which is to say folded along the edges and bent forwards on the plane, which resulted in a fl at folded plate element. This stabilised shell can then be combined with other shells in order to create a structured space.

1.5 From the fi rst experiences with the application of

fi bre-reinforced polymers up to modern buildings

In the 1960s, knowledge of the composite building component of fi bre-reinforced polymers was rather fragmentary. Nevertheless, makers of motorboats, sailboats and yachts began to apply this new, mouldable mate-rial for their products. By the time fi bre-reinforced polymers had ultimately trumped wood as a material for yacht construction in the 1980s, applied knowledge had been acquired concerning long-term usage in high-stress areas. Today, the racing sailboats of the America’s Cup would be unthink-able without the high-performance carbon fi bre used for the masts and hull. Sailing yachts with fi breglass reinforcement, even 30 years old, are still highly coveted.

There are many well-known experimental structures from the middle of the twentieth century. Transparent corrugated panels were used quite early for the roofi ng of simple buildings, in ceilings with corrugated metal or asbestos plates. The ability of light to pass through the material was not suffi cient and, unfortunately, the material aged rapidly over several years. In 1954, Richard Buckminster Fuller built a metal-free radar receiver 11 metres in diameter on Mount Washington with triangular fi breglass-reinforced polymer panels. Heinz Isler, known in Switzerland for his thin

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concrete shells, included skylights made from 3.5 mm thick translucent fi breglass-reinforced polymer. Further early works starting in the 1960s are still in existence, although some of them are in poor condition, such as the ‘Tournesol’ covered swimming baths from 1972. These are composed of elemental and pivoted roof constructions from fi breglass-reinforced polymer, and were a type of serial construction at several locations in France. Some of the constructions are still in service (as at Obernai, Alsace), whereas others have disappeared. The ‘Futuro’ in 1968 from Matti Suuronen, presented at the Finnfocus-Export Fair in London, even today commands record prices from its enthusiasts. Other buildings by Suuronen, one of the pioneers of construction with fi breglass-reinforced polymers, were elemen-tal petrol stations and living spaces.

The success of the early fi breglass-reinforced polymer constructions was due to the fact that a construction material had been found for the techno-logically faithful 1960s and 1970s that was not only synthetic and producible in vast quantities, but also seemed to have no limits with regard to its form-ability. The material matched the city and living utopia of this era. The early demise of this construction method was heralded by the oil-price shock in the second oil crisis of 1979, when the price of oil temporarily sky-rocketed to almost six times its previous price and the increasing cost of maintaining a staff responsible for hand lay-up techniques of fi bre compound construc-tions simply became uneconomic.

The resistance of fi bre-enhanced polymers to salts and acids has, however, kept them in active use in technical buildings. Silos and large halls are quite often raised using these materials. In the meantime, the industry has been able to gather a great deal of knowledge and experience through the con-struction of turbine blades for wind farms and the establishment of this technique in boat and yacht construction, as well as in the automobile, aeronautics and aerospace industries.

In modern architecture, fi bre-reinforced resins are beginning to be applied again, since it is possible to use this material to achieve the forms one can fashion using CAD software. The manufacturing technologies are so advanced that the traditional drawings common to construction sites are almost incapable of presenting the three-dimensionality of the fi nal product. Data is delivered to multiple axis milling machines, which are able to create positive models in small series. It is merely the production, still in many cases limited to hand-laminating processes, that is not capable of delivering satisfactory and cost-effi cient mass-production of the building components.

Thus applications such as the facade slats at Foster’s Walbrook in London or at Herzog de Meuron’s Elbe Philharmonic Concert Hall in Hamburg remain as highly individualised prestige objects. However, the automobile and caravan industry has long since proven that the creation of lightweight

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Introduction 9


systems for special applications is an approach that can be a fi nancial success. In architecture, interior elements are established applications that are generally inspired by furniture design from Eero Saarinen or Eero Aarino. On the other hand, for applications where the weight of the object is decisive, the knowledge gained with this material is already being suc-cessfully applied, as with bridges or easily moved roofi ng.

Another fi eld of application of fi bre-reinforced polymers is external rein-forcing armatures of existing supporting structures, preferably installed with concrete ceilings, concrete girders and concrete columns. Carbon, fi breglass and aramid fi bres are usually applied as prefabricated strips or mats. The pre-stressing of bearing structures can also be undertaken with the help of externally applied fi bre-reinforced polymers.

1.6 Conclusion

The well-known possibilities of the use of textiles and fi bres in construction have developed into fi elds of application ranging from geotextiles to fi bre-reinforced concrete, concrete reinforcing armatures made of fi bre-reinforced polymers, usually carbon fi bre composites (CFCs), textile membranes and sheeting and to constructions made of fi bre-reinforced polymers as multi-layer composites. The present book is dedicated to the spectrum of building; geotextiles are excluded, since they are less com-monly used for building construction and are more common in earthworks, transit structures and landfi lls.

Architecture creates living space, which is conceived by visionaries and carried out by sensible project managers or in the worst case matures through mere indifference. The Metropolis scenario, where some live ‘above’ in the light and others ‘below’ in the dark, refl ects the fears and fantasies of the pioneers of modern architecture during the epoch of Fritz Lang. The materials available to us today for lightweight construction are seen in this fi lmic black-and-white glimmering sadness at best as compo-nents of the fl ying objects. Buildings were still envisaged in terms of stone and concrete, with canyons and caverns between homes. The developmen-tal history of architecture ranges from the most simple and lightweight demountable homes, such as the yurts of Siberian nomads, to the stone buildings of the French military engineer Vauban and to the ultimate pro-gression to the massive. The Gothic cathedrals had the goal of positioning the heavy materials against the lightened heights and the impression of the construction, ‘hovering in the sky’. However, it was not until the invention of steel construction technologies in the eighteenth and nineteenth centu-ries that the materials seemed to disappear and the laws of gravity no longer apply. The best testimonies are the daring constructions of the Russian engineer Suchov and the Frenchman Eiffel. The ingenious metalwork of

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Jean Prouve in the middle of the twentieth century was summarised with the following: ‘que pense le matériau?’ – what does the material think? And last but not least, we are at the beginning of the seemingly endless possibili-ties of computer-assisted drawing and calculation programs and the ways in which these tools can infl uence building with textiles, fi bres, sheeting and combination materials.

Growing demands placed upon the carbon dioxide balance, energy sources, recyclability of building components, scarcity of raw materials, the increasing price of oil, existing and coming international confl icts about the resources of our planet: in light of these concerns, optimised and energy-saving construction methods are becoming more and more important. That textiles and polymers will be of great signifi cance in the construction indus-try cannot be emphasised enough. This work can refl ect the state of the art in the fundamentals and with examples while forecasting future tendencies. Outlooks to the discoveries of biomimetic research are therefore allowed and desirable; our repertoire of natural discoveries is something that our technological focus has ignored for long enough. The construction industry is allowed to get excited about the qualities of future fabrics and composites with which products can and will be created that will change the very nature of building – from the ground up. With great strides, production technolo-gies will realise the potential of these innovative lightweight construction materials. Building will distance itself more and more from the placement of one stone upon another. The highly insulated facades of our modern low-energy buildings stand only for the ‘as if’: as if behind the facade there were a massive wall. But instead of this wall, there are warming insulation materials 20 cm thick, and – rather than mortar between the bricks – the insolation packages form a new simplicity that is characteristic of modern building design. Most complex designs provide buffer zones, fl exible roofs and walls, the sheathing of existing massive or shell structures: this is the current fi eld of application for textiles and polymers. Utopia need not worry about using composites of natural and artifi cial fi bres. Combinations of artifi cial materials and sustainable raw materials are now being exploited in many technological fi elds. As attested to by the example of the cut-resistant Dyneema fi bres interwoven with coconut fi bres, combinations of artifi cial and natural fi bres have already arrived in technical applications.

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13

2Types and production of textiles used for

building and construction

M. MILWICH, Institute for Textile Technology and Process Engineering Denkendorf (ITV), Germany

Abstract: Already many lightweight membrane structures are in existence, and an increasing number of them are planned for the future. In this chapter different materials and coatings for textile membranes are introduced and discussed, which have to fulfi l a wide range of properties. The main task of the membranes is to act as a barrier function against water, IR- and UV-radiation and excessive heat, and they should provide, amongst others, mechanical stability, light transmission and resistance to environmental impact.

Key words: textile membranes, building textiles, barrier function, coatings.

2.1 Introduction

Already many lightweight membrane structures are in existence, and an increasing number of them are planned for the future, e.g. football stadium roofs. For such structures the combination of materials produces widely differing properties. Some projects are very cost-effective, while others are used for more expensive building constructions. Some constructions are of a temporary nature, some are erected at a fi xed location; some are required to be portable, while others may remain in place for decades. Textile roofs or walls may be open or closed according to the time of day or the position of the sun; others stay fi xed in one position. Some materials are required to have high translucency; others may be designed for maximum insulation.

What specifi cations are required for these textiles or membranes? Building textiles and fabrics have to fulfi l a variety of functions. The most important is the ‘barrier function’, which is an umbrella term for a combina-tion of several properties. In architecture, this may be described as ‘textiles with blocking or regulative properties regarding environmental infl uences’ and it should provide protection from rain and sun, while allowing a certain amount of warmth and light to penetrate the membrane. In some cases, water vapour must be able to pass through the membrane in order to main-tain a good climate within a room. Sound should be largely dampened and the outside surface of the membrane should be self-cleaning.

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Membranes are thin fl exible fi brous or foil materials which are stabilised solely by tension forces and have a constant stress rate over their entire thickness. In contrast to other materials like glass panes, wood, stone or concrete, membrane structures are extremely light because the ratio of material weight to tensile strength is excellent. The low weight of the mem-brane material also reduces the weight of the primary supporting structure. Because textile membranes are made of thin and fl exible materials, usually a double curvature and biaxial pre-tension is needed to stabilise the structure.

To determine a constant and isotropic stress rate, only a minimal surface area is required for the calculation; nevertheless it is necessary to consider differing strengths in the warp and weft directions of the fabric and, to some extent, of the foil. This should preferably be taken into account in creating the cutting pattern when additional pre-stresses have to be induced in the membrane to create structural shapes which could not otherwise be developed.

The most widely used classical membranes are made of PVC-coated polyester fi bres and PTFE-covered glass fi bres, while new, stronger and more lightweight textiles made of high strength polyester (LCP) or PTFE may be combined with new types of coatings like silicones for greater translucency. High strength, translucent foils are developed for pressurised cushions. The growth in the textile building market has an ongoing major impact on the global textile industry. In recent years new fi bres, yarns, constructions and coatings for the buildtech textile market have been developed.

In addition to familiar materials, microfi bres made from different poly-mers offer innovative new functional textiles. Fibres or textiles fi nished to provide antimicrobial or temperature control properties also open new markets.

New exciting materials and constructions are to be expected in the future. So-called gradient textiles will show the way to even more sophisticated lightweight membrane solutions. In gradient textiles, the fi bres are not arranged in a regular pattern but are laid out according to the lines of tension which occur in the fabric due to the action of outer forces. An example is the NASA Ultra Long Duration Balloon, which is made of a 38 micron polyethylene fi lm combined with reinforcing PBO tendons deployed between the base and apex end fi ttings, supporting the foil during visco-elastic creep due to stress and temperature. It will be used to carry scientifi c payloads up to altitudes of 40,000 m.

Although there are, in principle, not a great many types of fi bres and coatings actually used for buildtech applications, the fi bres in themselves offer a multitude of adjustable properties from which to choose. Each component of the fabric can be manufactured to meet the specifi c need of

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Types and production of textiles used for building and construction 15


the intended application. The adjustment of properties starts with natural fi bres from the country of origin and its staple fi bre spinning conditions, synthetic fi bres from the choice of basic monomers, the settings of different parameters in polymerisation and spinning, multiple possibilities of choice and application in spin fi nishing, the extent to which fi bres may be elon-gated, and the post-treatment applications to spun fi bres.

Selecting a textile, whether for building or for other everyday use, is not only a matter of fulfi lling the technical demands of a specifi c application. It must also take account of trends, fashions, feelings, and the expression of opinions and styles. For example, a decision may sometimes be made to choose a ‘green’ natural fi bre rather than a synthetic fi bre with the best properties.

In the case of building textiles – as in other technical textile applications – a detailed specifi cation sheet must be drawn up and a selection made from a variety of materials, properties and prices. The relevant properties are:

• Barrier function against water, IR- and UV-radiation and excessive heat• Mechanical stability (tensile strength, creep, fatigue limit, tenacity, fold-

ability, based on weight)• Light transmission factor, translucency• Resistance to environmental impact (UV, ozone, humidity, tempera-

ture, corrosive gases) which affects the life span• Sound damping• Burning behaviour• Ease of cleaning, dirt-repellence, self-cleaning• Capacity to take colour and print• Recyclability.

2.1.1 Fibres

Figure 2.1 classifi es fi bres according to their provenance.

Natural fi bres

Natural fi bres include cotton, wool, hemp, fl ax and many others. Despite discussion about variable quality in different batches from different years, distributors offer the assurance that by mixing fi bres from differing crop years and origins, almost 100% consistency in fi bre properties is achieved.

Fibres from natural polymers

The most common polymer fi bre from natural sources is viscose, which is made from cellulose fi bres obtained from wood. Other modifi ed cellulose-based fi bres are cupro, acetate and triacetate, lyocell and modal. Less

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common natural polymer fi bres are made from rubber, alginic acid and regenerated protein.

Fibres from synthetic polymers

Many synthetic fi bres are available such as organic fi bres based on petro-chemicals. The most common of these are polyester, polyamide, acrylic and modacrylic, polypropylene, polyvinylalcohol, the segmented, high elastic polyurethanes (elastanes) and high performance fi bres like glass, carbon, aramid, LCP, UHMWPE and PBO.

Fibres from inorganic materials

Inorganic man-made fi bres include glass, metal and ceramic.

2.1 Classifi cation of fi bres.

Fibres

Organic

Natural

Man-made

Acetate CAModal CMDTriacetate CTAViscose CVElastodiene(rubber)

ED

Rayon RA

Polyethylene PEPolypropylene PPPolyamide PAAramid ARPolyester PESPolyethylene terephthalate PETPolybutylene terephthalate PBTPolyacrylonitrile PANPolyvinylchloride PVCElastane ELPolytetrafluoroethylene PTFEPolyimide PI Polyether-ether-ketone PEEKPolybenzimidazole PBIPolyphenylenesulfide PPSLiquid crystal polymer LCPPoly(p-phenylene-2,6-benzobisoxazole)

PBO

Ultra-high molecularweight polyethylene

UHMWPE

Carbon fibres CF

Asbestos AsbCeramic CFGlass GFMetal MF

Synthetic, based onnatural polymers

From synthetic polymers

Cotton JuteFlax Ramie Sisal Hemp

Crop

Mineral

Silk Wool

Animal

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2.1.2 Fibre characteristics and properties

Fibres used in buildtech and other demanding applications have special adjustable profi les enabling them to fulfi l the requirements of a wide range of different applications from functional to high-end technical textiles in aerospace. The production of man-made fi bres offers many processes and parameters creating a wide range of properties.

The chemical composition of the fi bres, their geometry and the spinning conditions defi ne the range of properties: glass transition temperature, melting point, heat stability, combustibility, specifi c electrical resistance, resistance to environment (humidity, chemical, biological, radiation), dye-ability, solubility and the mechanical properties which are listed in the following chapter. The main characteristics of fi bres are listed below.

Cross-sectional shape

Many shapes are to be found in natural fi bres. Cotton fi bres are C-shaped and have a hole in the centre. Flax and hemp are relatively smooth. Wool fi bres are more or less round but have a scaled surface and may be used for felting, a process in which the scales are made to adhere to each other by mechanical forces, assisted by the application of a surface solvent chemical.

Man-made fi bres are normally spun as continuous fi laments by means of spinneret technology. The cross-section and surface of these fi bres can be widely modifi ed, particularly when different spinneret cross-section geometries are utilised: from round to profi led, solid to hollow, smooth to structured or crimped. The cross-section has a considerable effect on visual properties such as lustre, colour, transparency and cleanability and on the physiological properties of moisture transfer and heat insulation.

Melt-spun fi bres can be extruded in different cross-sectional shapes (round, trilobal, pentagonal, octagonal and others). Trilobal-shaped fi bres refl ect more light and give an attractive sparkle to textiles. Stains are less detectable on pentagonal-shaped and hollow fi bres. Octagonal-shaped fi bres offer glitter-free effects. Hollow fi bres trap air, creating insulation properties which are better than those of down and are also effi cient in transferring moisture.

In bicomponent spinning, two strongly bonded (but separable) polymers of different chemical and/or physical structure are processed into single fi laments by means of special spinnerets, e.g. side-by-side type (S/S), core-cover type (C/C) or matrix/fi bril type (M/F) (see Fig. 2.2). Bicomponent spinning offers the best opportunities for the production and development of micro- and nanofi bres by the use of matrix/fi bril

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types. By removing the matrix component with chemicals, one or both fi bril components will remain as a very thin fi bre. If the components are arranged like a cake, mechanical forces can separate the pieces of the ‘cake’ into microfi bres.

Fibre thickness/diameter

The diameter of natural and synthetic fi bres usually ranges from 7 to 20 μm. Microfi bres and bicomponent split fi bres allow a range of 3–7 μm and fi ner. Tightly woven textiles made of fi ne microfi bres are watertight, but are permeable to water vapour. Melt-blow and fl ash spinning fi bres have a 1 μm diameter. With electro-spinning, a diameter of 100 nanometres or lower can be produced. These fi ne fi bres are very suitable for the fi ltering of small particles.

Because the measuring of fi bre diameter is diffi cult, the fi neness of a fi bre is specifi ed by the ratio of the mass of the fi bres to a certain length of the yarn. The value 1 dtex means that 10,000 m of a fi bre weighs 1 gram. Via the density of the fi bre, this value may be converted into the actual nominal fi bre diameter and vice versa:

• Fibres (thick) >6.7 dtex• Fibres (mean fi neness) 6.7–2.2 dtex• Fibres (fi ne) 2.2–0.9 (1.2) dtex• Microfi bres 0.9 (1.2)–0.3 dtex• Super-microfi bres <0.3 dtex

Side-by-side type

Core–cover type

Matrix/fibril type

Cake type

2.2 Types of bicomponent fi bres.

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Fibre length

Natural fi bres tend to have a certain length which follows a typical gaussian distribution and is called the staple of a fi bre. Synthetic fi bres are spun as continuous fi laments. They may be left in this condition (mostly for techni-cal textiles) or be cut to lengths of 40–60 mm and combined with natural fi bres for the staple fi bre spinning process (mostly for clothing). It is self-evident that continuous fi laments have a higher strength than the staple yarns. Silk fi bres or spider fi bres are natural continuous fi laments and also have a very high strength.

Number of fi laments

The number of fi laments in a yarn may vary from a single monofi lament to thousands of fi laments in multifi lament yarns. Some carbon fi bre rovings consist of 50,000 fi laments.

Mechanical–physical

There are many signifi cant mechanical–physical properties, e.g. tensile strength, elongation at break point, tensile modulus, elastic recovery, tension–relaxation/creep under static and dynamic loading, specifi c weight, shrinkage, moisture absorption and knot strength.

High strength and high modulus fi bres like polyester, glass, aramid, UHMWPE, PBO and carbon are required for the advanced mechanical demands of buildtech. Their high linear tensile strengths result from the polymeric structure and the bonds between the molecular chains (van der Waals and hydrogen bonds). The strength of UHMWPE results from the parallel linear arrangement of its very long polymeric chains. Other poly-mers derive their strength from incorporated aromatic rings, a larger number of rings usually making for greater strength. PBO has a so-called polymeric ladder structure of aromatic rings directly connected to each other and therefore has very high strength and modulus. The advantage of the high modulus of glass and carbon fi bres is accompanied by a weak resistance against shearing, folding and abrasion. Therefore these fi bres should be only be used in a coated form.

An overview of important fi bre properties is given in Table 2.1. The tensile strength of the fi bres is given there in:

• GPa, which is a value based on the cross-section• N/tex, which is a value based on the density of the material. N/tex results

from dividing GPa by the density. Steel has relatively high values in GPa, but because of its high density, it has low values of N/tex measured in tensile strength and Young’s modulus in comparison to high strength polymeric fi bres such as aramid, LCP and UHMWPE.

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Table 2.1 Important fi bre properties in standard climate

Density (g/cm³)

Breaking elongation

Tensile strength

Tensile strength

Young’s modulus

(%) (N/tex) (GPa) (GPa)

Silk 1.25 23 0.34 0.43 11Wool 1.30 22 0.12 0.16 3.5Cotton 1.54 7 0.35 0.54 12Hemp 1.48 1.6 0.57 0.84 30Viscose 1.52 20 0.23 0.35 7.3Polypropylene 0.91 20 0.65 0.06 1.52Polyamide 1.14 20 80 0.9 6Polyethylene terephthalate 1.38 13 80 1.1 3.4–21Aramid (m-type) 1.44 15–30 0.48 0.7 36Aramid (p-type) 1.45 1–4 2.05 2.9 127Polybenzimidazole (PET) 1.4 30 0.28 0.38 56Liquid crystal polymer (LCP) 1.47 3.3 2.17 3.2 91Ultra-high molecular weight

polyethylene (UHMWPE)0.97 2.9 3.29 3.2 171

Polybenzobisoxazole 1.56 2.5 3.71 5.8 270Polyether-ether-ketone

(PEEK)1.3 30 0.6 0.78 5–6.2

Polytetrafl uoroethylene (PTFE)

2.2 35 0.18 0.34 0.3

E-glass 2.54 3.5 1.35 3.5 72S-glass 2.5 3.5 1.85 4.6 86Steel 7.86 1.1 0.96 7.6 200Carbon high strength (HS) 1.78 1.6 2.1 3.75 240Carbon high modulus (HM) 1.85 0.7 1.32 2.45 400

Surface-related properties

Properties related to the surface chemistry or surface area are hydrophilic/hydrophobic: wettability, oleophilic/oleophobic, soil repellence, water pen-etration, aesthetics, antibacterial function and friction behaviour.

Thermal stability

Commonly used natural and synthetic fi bres are classifi ed as easily combus-tible materials, whereas most of the high performance fi bres, e.g. aramids or polyetherimids, are classifi ed as highly fl ame-resistant and are self-extinguishing when the fl ame is removed. The fl ammability of fi bres may be characterised by their limited oxygen (LOI) and spontaneous igni-tion temperature. The LOI provides information on the minimum atmo-spheric oxygen content which is needed for burning after the material is ignited (Table 2.2). The spontaneous ignition temperature is the lowest

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Table 2.2 Temperature resistance of fi bres

Fibre Flash point (°C)

Spontaneous ignition temp. (°C)

Limiting oxygen LOI

Melting temperature (°C)

Degradation temperature (°C)

Cotton 288 350 19 >190Wool 224 570 25 >150Polyamide 354 425 20 220Polyester 372 485 22 260PPS 500 39–41 285–334PTFE >550 95 >400m-Aramid

(Nomex)>500 >600 28 >370

PBO (Zylon) 68 >650PBI 36–43 >450–550PEEK 35 >335Melamine

(Basofi l)30 >370

Glass fi bres 900–1300Carbon fi bres 3300Quartz fi bres 1930Metal fi bres 600–3380

temperature at which the fi bres start to burn, whereas the fl ashpoint is the lowest temperature at which a combustible product ignites when approached by a fl ame.

The burning behaviour of textiles is strongly affected by the structure of the textile fabric (open, closed, as in woven or warp-knitted), by the fi bre and textile surface (raised, calendered) and by the weight (g/m2). Dyes, spin fi nishes and sizing/impregnation agents are used to change the burning behaviour.

Chemical stability

A defi ned lifetime and product security has to be guaranteed to end-users by producers. During the lifetime of building textiles, they will undergo environmental degradation from gaseous or liquid chemicals, ultraviolet radiation, wind forces, humidity, dust and salts, thus altering the properties of the product. Typical examples of such damage are loss of strength/pre-tension, changes in permeability, colour, lustre and dimensions, embrittle-ment and formation of cracks, as well as changes in electrical and thermal conductivity, burning behaviour or humidity transport. Therefore fi bres and coatings have to be inherently resistant or should be made resistant against such attacks. Nevertheless, the quality of materials to withstand environmental conditions at the building site is always in confl ict with the

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cost of generating those properties. Man-made fi bres are more resistant to acids and alkalis than natural fi bres.

2.1.3 Production of fi bres

Most synthetic and cellulosic fi bres are manufactured by ‘extrusion’ – forcing the highly viscous polymer through a varied number of tiny holes of a spinneret to form continuous fi laments. As the fi laments emerge from the holes in the spinneret, the liquid polymer is initially converted to a rubbery state and then solidifi es. There are four methods of spin-ning endless fi laments: wet, dry, melt, and gel spinning. Those processes are called primary spinning, in comparison to secondary spinning, where short staple fi bres (40–80 mm in length) are formed and twisted to form yarn.

Melt spinning

In melt spinning, thermoplastic polymers (i.e. polymers which soften and melt when heated) such as polyamide or polyethylene terephthalate are made molten or liquefi ed in an extruder and are forced through the spinneret by a spinning pump. The fi laments are then solidifi ed by air-cooling.

Wet spinning

Wet spinning is used for non-thermoplastic polymers like viscose, cupro, lyocell, triacetates or aramids, which have to be dissolved in a solvent to transform them into a liquid state. In wet spinning, the spinnerets are sub-merged in a chemical bath. A spinning pump forces the polymer solution through the spinneret. A diffusion processes in the chemical bath precipi-tates the polymer solution to a gelatinous state and fi nally to a solid state. The spinning speed (50–150 m/min) is much lower than in the other spin-ning processes. This process is gaining in importance in the production of fi bre types with special properties (high temperature resistance, fl ame retardation).

Dry spinning

Dry spinning is also used for solute polymers. However, instead of precipi-tating the polymer by a chemical reaction, solidifi cation is achieved by evaporating the solvent in a stream of air or inert gas. Typical fi bres spun by this process are acetate, triacetate, acrylic, modacrylic, PBI and elast-hanes (Spandex).

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Gel spinning

Gel spinning is used to obtain high strength fi bres like UHMW polyethyl-ene and LCP. The polymer chains are not completely separated into a totally liquid state, but are bound together at various points to form a so-called ‘liquid crystal’. This results in strong inter-chain forces in the extruded fi laments which signifi cantly increases the tensile strength of the fi bres. In addition, the liquid crystals are aligned along the fi bre axis by the shear forces during the extrusion process. This high degree of orientation further enhances the strength and the Young’s modulus. The process can also be described as dry–wet spinning, since the fi laments fi rst pass through air and then are further cooled in a liquid bath.

Stretching

After spinning, the fi brils are usually stretched to orient the polymeric chains along the fi bre axis. In some cases, stretching is conducted even after the fi brils are in a solid state. This procedure enhances strength and reduces strain on the fi laments.

Twisting

Single fi laments are merged into multifi laments and wound on a spool. These fi laments may then be twisted to protect them from the successive textile processes or to give the multifi laments special properties, e.g. a desired stress/strain behaviour. The twist may vary between one and several hundred turns per metre. To compensate for weak spots in the yarns, two multifi laments may be twisted together to form a ply yarn.

Cutting

Where polymeric fi bres are mixed with natural fi bres, the continuous mul-tifi laments are cut into lengths according to the mean length of the natural fi bres. The fi bre-mix is then made into yarns via ring spinning, rotor spin-ning or air-jet spinning.

2.1.4 Changing fi bre properties by post-treatment and fi nishing

In order to obtain functional fi bres and textiles to meet the special require-ments for buildtech applications, a large variety of properties can be engi-neered by fi nishing and post-treating fi bres, e.g. for dirt or oil repellence, UV-protection, fl ame retardance, higher tensile strength or abrasion resistance.

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Fibre shape

The texturing process converts fl at fi lament yarns into bulky yarns, increas-ing the volume and/or stretchability of the yarn (Fig. 2.3). Texturing changes the textile character of the originally fl at yarns by crimping and has opened up new fi elds of application which originally were covered by staple fi bre yarns. Several processing techniques have been developed for the produc-tion of textured yarns, mechanical/thermal (torsional crimping), chemical/thermal or mechanical alone. Texturised yarns are generally more stretch-able and have a higher capacity for moisture absorption and moisture transport, better air incorporation, reduced lustre and an increased resis-tance to pilling.

Dimensional stability

The dimensional stability of synthetic yarns and textiles can be considerably enhanced by a thermosetting process, i.e. heat treatment under dry heat, steam or hot water. Thermosetting may be undertaken either with or without applied tension. Thermally treated fi lament yarns and staple fi bres show less heat shrinkage, have a reduced tendency to crimp and show improved recovery from creasing.

Hydrophobic properties

Water-repellent fi nishing is obtained by the use of hydrophobic agents such as paraffi n emulsions containing metal salts such as those of aluminium and zirconium. The positively charged metal salts affect the alignment and adherence of the negatively charged paraffi n particles to the fi bre. The outward-looking hydrophobic paraffi n particles prevent the fi bres from becoming soaked with water. Other systems consists of quaternary ammonia compounds, modifi ed fatty acid methylol melamins or silicones.

2.3 Flat and textured fi laments.

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Dirt and oil repellence

Dirt repellence is a desirable property for a large number of textile products used in outdoor applications. It can be obtained by fi nishes or coatings, although the smoothing of the textile surface by calender rolls is also known to be an effective method. For the repellence of oily contamination, silicon compounds, carboxymethyl celluloses and fl uorocarbon fi nishes are applied to the fi bres or to the textile material.

Heat and UV protection

Suitable UV and heat protection can be achieved by the textile itself. Heat and UV protection increases with the density of the textile and with the use of bulky microfi bres. Cellulose fi bres and silk provide lower UV protec-tion when compared to woollen materials or to polyester with aromatic components. Increased UV protection is obtained by the incorporation of pigments like titanium dioxide into the fi bres. This absorbs and refl ects UV rays and creates a sun protection factor of 50. Finishing agents are alkyl p-aminobenzoates and cinoxates which also absorb UV radiation and convert it into heat.

Low infrared emission (low-e) coatings or fi nishes are transparent to visible light but opaque to infrared radiation, thus reducing total heat fl ow. Low emission may be achieved by the use of very thin metal or metallic oxide fi lms, e.g. silver, tin oxide or alumina coating, which are almost transparent.

Flame retardance

Natural fi bres and most man-made fi bres are insuffi ciently fl ame retardant, whereas high temperature resistant fi bres (HT-fi bres) resist temperatures higher than 500°C. Flame retardance can be obtained by certain fi nishes, which consist of aluminium, antimony, ammonia, ammonium phosphate, phosphorus, chlorine or bromine. A special PET fi bre may be made per-manently fl ame resistant by incorporating a small quantity of phosphoric organic molecules on the molecular level, increasing the LOI from 22 to 36. In addition to building textiles, its applications are in sleeping bags and fi llings, protective clothing and coverings, mobile vehicles, and military and racing garments. These fi nishes hinder or prevent combustion by means of several mechanisms:

• The formation of easily combustible pyrolysis products is reduced by a dehydration effect of phosphor–nitrogen compounds in the fi nishing agent.

• Release of gases (H2O, CO2, HCl, etc.) supersedes the oxygen, thus extinguishing the fi re.

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• Poorly combustible fi bre coverings (e.g. AlO) hinder pyrolysis.• The release of radicals (Cl, Br, etc.) interrupts the chain reaction of

combustion.

Antistatic fi nishing

Synthetic fi bres take a static charge because they are non-conductive and only absorb small quantities of water. This effect is reinforced by low air humidity, particularly in winter, and soiling may be increased. Antistatic fi nishings reduce the high electrical resistance of fi bres. These consist of hydrophilic surface active polar compounds (tensids), carbon particles, electrically guiding polymers or salts. Textiles may also be made antistatic by incorporating metallic or metallised fi bres or conductive carbon fi bres which are coated with polyamide.

Antimicrobial and antifungal fi nishing

Textile fabrics are fi nished with effective antimicrobial substances like ammonium, chlorinated diphenylethers (Triclosan), bisphenols, silver zeo-lites or cyclodextrines. Silver is an effective antimicrobial material and the constant release of a small amount of silver ions will kill bacteria or fungal growth. Silver particles may be added to the molten polymer or a silver coating may be applied to the fi bres by a galvanic process.

Titanium dioxide is a well-known material for creating matt-fi nished fi bres. Surface-activated titanium dioxide, when used for the fi nishing of fi bres, produces a photo-catalytic self-cleaning effect because organic mate-rials will decompose on the titanium dioxide surface under the infl uence of light. When used as a coating, activated titanium dioxide forms a super-hydrophilic surface, on which water makes a thin layer rather than forming droplets. Consequently, there is no misting of the surface.

2.1.5 Fibre materials for buildtech applications

Fibres for buildtech applications require special properties due to the demands of the respective applications as outlined in other chapters. Summarising the properties, they should constitute a barrier to rain and excessive heat, have high specifi c strength, should be highly resistant to severe weather conditions, chemicals and UV radiation, should not burn and should be easy to clean. In principle, a decision has to be made between competitively priced natural or technical fi bres with a reduced life span (e.g. PET) or high performance fi bre materials which may cost more than twice as much but offer a much longer life span and will meet a more demanding standard (e.g. PTFE, aramid).

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Cotton may be given a fl ame retardant fi nish and is mainly used for indoor applications. Cotton is subject to fungi and bacteria. When wet, it swells and offers a higher strength, and it may sometimes be used for tem-porary outdoor applications.

Polyethylene terephthalate (PET) offers high strength and tenacity and has the highest bending recovery values. It is resistant against chemicals and does not absorb a signifi cant amount of water which, together with its relatively low price, makes it highly suitable for buildtech applications. However, PET fi bres exposed to UV radiation will lose 50% of their strength after two years and therefore need to be protected against UV radiation with colour-pigmented PVC coatings. Because the fi bre elonga-tion is higher than in glass or aramid, folds produced in manufacture or installation can be stretched out.

Liquid crystal polymers (LCP) are highly ordered ‘crystalline’ aromatic polyesters with high mechanical strength. They are exceptionally inert, having very high thermal and chemical stability, are highly resistant to UV radiation and are inherently fl ame retardant and antistatic.

Polyamide (PA) fi bres have high strength and tenacity, excellent abra-sion resistance and higher elongation than PET. Water absorption of PA 6 and PA 6.6 is relatively high (up to 6%), while that of PA 12 is only 0.3%. Together with UV radiation, the absorbed water may split the relatively weak peptide bonds of polyamide, so it is of little use in outdoor applications.

Aramids have been developed from the need to enhance the chemical stability of polyamides. Because of the stability of aromatic rings, aramids also have higher tensile strength and thermal resistance than aliphatic poly-amides. These qualities make aramids popular for use in impact resistance applications. However, aramids – along with PA – have low UV resistance. If used in outdoor applications, they must be heavily coated to protect against UV radiation.

PI (polyimide), PEI (polyetherimide) PPS (polyphenylene sulfi de), PBI (polybenzimidazole) and PEEK (polyether-ether-ketone) – among others – are examples of modern fi bres with high thermal stability and excellent chemical and fi re resistance properties as a result of the high stability of conjugated aromatic structures. Due to both high raw material costs and a demanding manufacturing process, these materials are noted for their high cost. To reduce cost, less expensive aramids are added in producing fabrics.

PBO (poly-p-phenylene-2,6-benzobisoxazole) is a so-called ladder shtructure with repeating aromatic structures. It has a very high thermal stability (melting point 650°C) and excellent chemical and fi re resistance properties. It has the highest specifi c tensile strength of all materials but is susceptible to humidity and UV radiation.

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Glass fi bres have been manufactured since the 1930s. They offer a wide range of properties and may be found in many applications, such as insula-tion batting, fi re-resistant fabrics and reinforcing materials for plastic com-posites. Continuous fi laments of optical quality glass have revolutionised the communications industry in recent years. In building applications, glass fi bres are used in high performance textile membranes. Glass has a high strength and low elongation and displays very low creep. Because the mate-rial is brittle, it should be handled carefully and is not recommended for folding applications.

Melamine fi bres are primarily known for their inherent thermal resis-tance and outstanding heat blocking capability in direct fl ame applications. This high stability is due to the cross-linked nature of the polymer and the low thermal conductivity of melamine resin. The dielectric properties and its cross-sectional shape and distribution make melamine ideal for high temperature fi ltration applications. It is sometimes blended with aramid or other high strength fi bres to increase fi nal fabric strength.

ePTFE (expanded polytetrafl uoroethylene) fi bres offer extremely high UV and chemical resistance coupled with good thermal stability. These properties can, in principle, be allocated to all fl uoropolymers and are due to the excellent binding force between the fl uorine atoms and the carbon atoms. PTFE and the other fl uoropolymers provide excellent translucency, are stain- resistant and easy to clean, and also have excellent self-cleaning qualities, so the fabric colours remain true. They it also have an extremely low coeffi cient of friction and are highly resistant to abrasion. Customised colours are available and the material is RF weldable. New ePTFE fi bres have a very high strength and a high Young’s modulus, and are between two and four times more resistant to tearing than PVC or PTFE/glass fabric. They may be woven into high quality textiles which are unmatched regard-ing folding cycles.

Stainless steel monofi laments and multifi laments have attracted growing interest for use as exterior and interior cover panels. They are available in many different diameters, starting from 16 μm. The disadvantage of steel in comparison to all other fi bre materials is its high weight, but stainless steel is weatherproof and gives the construction a high quality appearance. In very large membrane constructions, the tensile strength of the mem-branes is no longer suffi cient, so steel ropes and steel nets are attached to the textiles to carry the loads. The tensile strength of steel-reinforced fabrics reaches 30,000 N per 5 cm with a weight of 12 kg/m2.

Ultra-high molecular weight polyethylene (UHMWPE) is extruded by gel spinning and has very long chains and high molecular orientation. It com-bines high strength and chemical resistance with low weight. Because UHMWPE is in principle a polyethylene, its disadvantage is its low soften-ing/melting point and a tendency to creep under tension. Therefore it is not

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suited for membranes, but is increasingly used for ropes, particularly in offshore applications.

Carbon fi bres have a very low elongation and a high tensile strength but are very brittle. Their usual application is in fi bre-reinforced composites with a thermoset resin system. A new application of carbon fi bre reinforced polyamide is in the repair of buildings, bridges and pillars, where pre-stressed strips are glued to the underside of decks or to the surface of pillars, so preventing them from fully breaking down.

For a comparison of physical/mechanical properties see again Table 2.1.

2.2 Overview of textile formation technology

Textile formation processes offer different means of creating a product from fi bres and yarn. Each process and product has its own particular advantages and individual price. In order to create a product which best fulfi ls the technical and economic requirements of each application in build-tech, a developer must have knowledge of these details.

2.2.1 Woven fabrics

Woven fabrics (Fig. 2.4) are used in various fi elds. When compared with knitted fabrics, they show only a low degree of elongation in both direc-tions. High-tech textiles for buildtech are mainly produced in combination with high strength and high modulus fi bres. There is a demand for the development of lighter materials with optimised functions.

2.4 Woven fabric.

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Woven fabric is mostly characterised by its weight per square metre. Heavier weight fabrics usually offer greater strength because more single fi bre strands are incorporated in the textile. In outdoor applications, the weight of the woven fabric, e.g. with PTFE yarns, starts from 900 g/m2. Mean values are 1000 to 2000 g/m2 with strengths of about 5000 N if a strip of 5 cm is tested. Special fabrics are very light in weight and start from 200 g/m2 .

Weaving pattern and fabric density are important aspects of building textiles, defi ning translucency, watertightness and acoustics (sound damping). As an example, optimum watertightness can be achieved by weaving with double the number of warp threads (e.g. 100–130 per centi-metre) to weft yarns (50–65 per cm). A plain weave is more resistant to dislocation than a twill weave but less drapeable. It is possible to adjust elongations in the warp and weft directions to produce special properties in the fabric, but this can result in a wrong deployment of the textile.

2.2.2 Narrow textiles

Narrow weaving and braiding technologies (Fig. 2.5) are applied for the production of belts and ropes across a wide range of dimensions. Narrow woven belts, sewn-on textiles and foils can considerably enhance the maximum span length. Ropes are used to create tensile connections between textiles/foils and the larger elements of a primary construction.

2.2.3 Flat knitting, weft knitting and warp knitting

Knitted fabrics (Fig. 2.6) are more fl exible due to their mesh structure. Ready-to-use goods can be produced in a single processing step by means of electronically controlled fl at knitting machines (‘fully-fashioned technol-ogy’). The electronic selection of needles offers a great variety of pattern-ing. Warp/weft knitted textiles display reduced strength, higher elasticity, better shape retention and recovery from bending, and superior vapour transmission when compared with woven fabrics. They are used for indoor applications, e.g. in mixed-fi bre high stretch applications with normal elas-ticity (10–30% elongation) and elastane fi bres (400% elongation).

In contrast to the reduced strength and high elongation of standard knitted fabrics, elongation is reduced in weft-inserted warp-knit fabrics by inserting linear, uncrimped fi bres into the fabric, allowing the use of these fabrics in load-carrying structural applications.

2.2.4 Nonwovens

Nonwovens have taken an increasing market share in technical applica-tions, due to the use of new materials and process technologies. By direct

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2.5 Braided fabric.

2.6 Knitted fabric.

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spinning of nonwovens (spunbonds), weights as low as 15 g/m2 can be achieved. Heavier and thicker nonwovens are produced by aerodynamic techniques, hydrodynamic techniques or the carding and needling process.

Very thin fi bres for nonwovens can be produced by split fi bre technology. Bicomponent fi bres are processed into a nonwoven fabric and this is fol-lowed by a splitting process. The fi bres may be split mechanically by water jet technology or by the chemical dissolution of one component which leaves fi ne fi bres of the other component (Fig. 2.7).

Nonwovens are seldom used for permanent load-carrying constructions, but are typically used as insulating material. A special spunbonded polyster nonwoven is used in large quantities for wind and water resistant breath-able membranes in building applications.

Micro- or nanofi bre coatings are applied to the nonwoven substrate surface to create special surface properties (e.g. fi lter/barrier).

2.2.5 Spacer fabrics

During recent years, there have been new developments in the area of spacer textiles: ITV Denkendorf has developed a process in which two separated textile fabric layers, covered by transparent foils, are connected by a spacer fabric. Due to this specifi c construction, an air space is created which provides a high degree of heat and acoustic insulation. Spacer fabrics, laminated or coated with transparent foil on both sides, are increasingly used for transparent thermal insulation. Woven spacer fabrics can be pro-duced up to 600 mm in width and are used, sometimes with fi lling, for sound damping (Fig. 2.8).

2.7 Nonwoven.

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An interesting spin-off of the ITV development is the ITV Denkendorf solar heat collecting spacer textile, in which one of the coverings is black-ened to trap heat which is then transported by water fl owing through the spacer room which is then utilised in heating the building (Fig. 2.9).

2.2.6 Post-treatment of the textiles

After the textile formation process, some post-treatment steps usually remain to be done. The most important of these is a heat treatment process – called thermofi xation – in which the fabric is passed under tension through an oven. The cross-direction tensioning is carried out by clamping the fabric between two circulating chains, and the lengthwise tensioning is achieved by the winding-up roller in collaboration with the winding-off roller. The yarns and the textiles are thus heat-set and will not crimp during usage or washing. To reduce the pore size of the textile and to smooth the surface,

2.8 Spacer fabric.

2.9 ITV solar textile.

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the fabric is continuously pressed between two heated tandem calender rolls. Another means of reducing the pore size of the textile is to let it shrink freely during the heat treatment.

2.3 Foils for building and construction

Foils are used in high transparency applications. Because they have to transmit a load in architectural applications, foils are made of high strength and high transparency material. This high quality can only be gained by foil extrusion: the less expensive blow-fi lm technology delivers unsatisfactory results in strength and uniformity of thickness. If a micro-perforation is applied to the foils, they will offer very good acoustic absorption. Because the foils are very thin, a further advantage is their low thermal load in case of fi re.

Polyvinylchloride (PVC) foil has a low strength and creep behaviour and is therefore used only in indoor applications for illuminated ceilings or walls. It has very good printing properties.

High stretch PET foils are made by stretching the usual polyester materi-als. This process delivers lightweight foils with the excellent environmental stability of polyester and a high tensile strength, but they are not long-term UV-stable and must therefore be coated.

ETFE (ethylenetetrafl uoroethylene) foil is in principle the only material which is used in outdoor applications, because – unlike in other synthetic materials – there is no softening agent incorporated and the material is therefore highly stable and not affected by environmental impact. Tensile strength is relatively low, e.g. 600 N for 5 cm length at a weight of 2 kg/m2, the foils having a thickness of 0.1 to 0.25 mm. In most cases the ETFE foil is processed into pneumatic cushions. The low weight of the material allows fi ligree constructions and bigger span lengths than glass, though this is restricted to about 20–50 m2. When reinforced by rope nets, the size of the cushion can be up to 300 m2. The foil has a self-cleaning ability and better transparency than glass. ETFE may be easily printed on, for artistic reasons, for information, for advertising or for the printing of regular patterns for adjustable light transparency. When perforated and arranged in a double layer, it has excellent indoor sound-damping capabilities.

THV (tetrafl uoroethylene–hexafl uoropropylene–vinylidenefl uoride copolymer) foil has very high transparency and elasticity, but low strength, so it is mostly used as a covering for load-carrying nets. As a fl uoropolymer, THV foil may be welded and is non-combustible and not susceptible to contamination, nor is it affected by UV radiation or chemicals.

PTFE terpolymer is a liquid amorphous fl uoric polymer system, which hardens to a completely transparent layer at room temperature. There is

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no signifi cant light absorption from IR up to UV, so the material itself is not affected by radiation. Possible thicknesses range from 1 μm up to >100 μm. The material can be fi lled with any colours and functional pig-ments or nanoparticles (metallic effect, heat stop, broadband refl ectors, light emitting, surface hardeners).

Polycarbonate (PC) foil is used for illumination in ceilings or walls. The thermoplastic PC has a transparency like that of glass, may be coloured and welded, is dimensionally stable, has a high impact resistance and may also be used for indoor sound-damping by making perforations in the foil. Like ETFE, polycarbonate is also fl ame retardant.

2.4 Coatings for building and construction textiles

A large variety of desirable properties for membranes may be provided by the fi bres themselves or by their fi nishing and post-treatment before the production of the fabric. If these do not provide the required properties such as watertightness, dirt and oil repellence, UV protection, fl ame retar-dance or abrasion resistance, the fabric must be coated or laminated. Additionally an unweldable textile (e.g. PTFE) may have a weldable coating applied.

When adding a coating to breathable membranes, the coating must also be breathable, i.e. water repellent while permitting water vapour to pene-trate both membrane and coating. This property is produced by micro-porosity or by water vapour diffusion and results in improved climate conditions within the enclosed space.

Coatings may consist of one to three layers, depending on cost and quality. High quality coatings have a base or tie coat, an intermediate or fi ller coat, and fi nally a top coat. The base coat ensures adequate adhesion to the textile material. The intermediate coat is responsible for the system volume and the mechanical properties. The top coat determines the appear-ance and surface properties and also seals the surface.

Before coating, it is important to prepare the textile substrate by cleaning it thoroughly and applying an adequate heat-setting treatment. Large quan-tities of residue or fi nishing agents may disturb the adhesion and penetra-tion of the coating whilst an inadequate heat setting may result in stretching or shrinkage during drying or in subsequent use.

Basically, a coating line consists of an unbatcher, a coating/lamination unit, a dryer/stenter, a cooling zone and a batcher. The coating may be applied on one or both surfaces of the textile substrate, either by direct coating or by the easier process of foil lamination. Coating technologies are direct coating, the air doctor system, the table or rubber-blanket doctor system, lick-roller systems, reverse-roll coater, engraved-roller systems, rotary screen printing and foam coating.

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The basic chemicals for coatings are polymers which form a fi lm or cross-link on the fi bre or fabric, together with additives and auxiliaries. Additives may be pigments for colour or for the refl ection of UV or IR radiation. In the future, it will become possible to apply the fi ller as nanoparticles, thus creating a new class of properties.

In the fi rst step of a lamination process, a foil or fi lm is produced. This is then laminated onto the fabric, either by heat and pressure or by means of an adhesive. The laminated foil places considerable constraints on the fl exibility of the fabric but offers better protection than a coating and is self-cleaning.

Where the coating itself does not provide all the desired properties, ‘top coats’ or ‘top fi nishes’ will be applied as a fi nal environmental barrier, pro-viding UV stability, durability, inertness and self-cleaning attributes. Top fi nish choices include acrylics, acrylics/polyurethanes and PVF fi lms.

Acrylates are inexpensive materials suitable for waterproof coatings in lower quality applications but polyurethane (see below) is better suited for higher quality applications.

Polyvinylchloride (PVC) coating is widely used for its barrier function together with PET fabric. It is essentially a hard polymer, but its hardness, and thus its fl exibility, may be varied by the addition of softeners. However, softeners pose a problem because they can volatilise during use, thus leaving PVC in a hard and brittle state with microcracks, where soil may collect and chemicals or water can get to the polyester.

In polyvinylfl uoride (PVF), because of the fl uorine, the chemical bond is better than in PVC, so PVF is stronger and offers better chemical inertness and a higher service temperature range from −70°C up to 110°C. PVF contains no softeners, so it withstands environmental infl uences and its properties do not change over time. It is dirt repellent and resistant to bleaching and has a high light transparency. It is mainly used as a top coat to protect against environmental infl uences and extends the lifetime of a PES-fabric/PVC-coating/acrylic top coat system from 8–10 years to 12–15 years.

Due to its doubled fl uorine atoms, polyvinylidenefl uoride (PVDF), is even less affected by the environment than is PVF (including its property of fi re retardance) and stands between PVF and the superior chemical properties of PTFE. However, PVDF has far better mechanical properties than PTFE. It is also used as a top coat to protect PVC coatings against environmental infl uences.

Polytetrafl uoroethylene (PTFE) is available in highly concentrated dis-persions which have to be sintered at temperatures up to 400°C. This means that only glass fi bre substrates are suitable for PTFE coatings. Modifi ed PTFE types with thermoplastic properties can be welded. PTFE displays very good chemical stability but reduced mechanical stability. It is transpar-

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ent and resistant to ageing, weather conditions and UV radiation, and has an anti-adhesive surface which is self-cleaning.

Silicone elastomers and dispersions consist of polydimethylsiloxane with reactive groups. They are not thermoplastics, thus ruling out ultrasonic or heat welding. A lasting bond, therefore, is effected by means of silicone adhesive or adhesive tape. The surface of silicone coatings can be engi-neered to possess non-clinging/dry to non-slip/tacky properties. They are water-repellent, thermally stable between −50 and +200°C, fl ame-retardant, resistant to ageing and to chemicals, and highly transparent. It is also pos-sible to regulate the UV transparency of silicone. The properties of silicone coatings fall between those of PVC and PTFE. Compared to PVC, silicone offers double the lifetime, better transparency without yellowing, better heat resistance and better mechanical properties and is halogen-free, but it is more expensive and cannot be printed on. Compared to PTFE, silicone is more transparent and easier to colour, performs better at low tempera-tures, is easier to build up and is free from halogens. Despite these impres-sive advantages, its dirt-repellent properties are not satisfactory, so it is mostly used in indoor applications.

Polyurethane (PUR) shows high resistance to wear. Polyesterurethanes exhibit high strength combined with high fl exibility, good cold fl exibility and high elasticity, but poorer resistance to oxygen and light. In many cases PUR may be an alternative material to PVC. To produce a breath-able membrane, a porous coating is produced by PUR foam coating which is calendered after drying. A non-porous coating, in which water vapour diffuses through the coating, can be produced with water or solvent-based hydrophilic PUR using direct or transfer processes. Usually two to three coats are required. Foam application is a more diffi cult process.

PTFE terpolymer is mainly applied as a foil material, but because it is a liquid fl uoric polymer, it can also be applied as a coating or top coat.

Vinylidene fl uoride terpolymer (THV) provides a combination of perfor-mance and processing advantages in comparison to melt-processable fl uo-roplastics. It can be processed at a relatively low temperature, so it is even possible to coat polyester. It is suited for all laminating processes and shows high resistance to chemicals. It is highly fl exible and offers very good chemi-cal and permeation resistance to all outdoor weather conditions, halogens, inorganic and organic acids, hydrocarbons, alcohols and hydrocarbon fuels. It has exceptional optical clarity and transmittance, particularly in the UV and visible regions of the solar spectrum, and does not support combustion because of its high limiting oxygen index.

Perfl uoroethylene–propylene copolymer (FEP) is an amorphous elastic synthetic rubber and is used to smooth uneven surfaces of PTFE coatings after the sintering process on glass fabrics.

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Synthetic rubber (ethylene–vinylacetate rubber, EVM; ethylene–propylene–diene rubber, EPDM) – new formulas of these materials deliver coatings that are not affected by environmental impact (UV, ozone, humid-ity, chemicals) and have excellent light transmission (up to 80%). A silica fi ller provides high tensile strength, high fl exibility and very good foldabil-ity, even at low temperatures.

Low-emission coatings are special top coats which hinder infrared fre-quencies from passing through the membrane and reducing total heat fl ow by radiating down to the ground. Low-e coatings are transparent to visible light but opaque to infrared radiation. Low emission can be achieved by use of very thin metal or metallic oxide fi lms, e.g. silver, tin oxide or alumina coating, which are almost transparent. The metallic coatings additionally are able to refl ect light and UV rays.

2.5 Top coats for building and construction

In cases where the coating itself does not provide all the desired properties – mostly with PVC and also with silicones – top coats or top fi nishes are applied to form a fi nal barrier to the environment, providing UV stability, hardness, durability, inertness and self-cleaning attributes. Top fi nish systems apply a thin barrier layer of material to the exterior surface. This barrier layer minimises plasticiser migration and provides a hard surface which sheds dirt. The effectiveness and longevity of the top fi nish depends on its chemical make-up and on the thickness of the barrier layer applied to the surface.

Top fi nishes are formulated using clear acrylic, acrylic/vinyl or acrylic/polyurethane resins and are applied at a thickness ranging from 0.1 mm to 0.4 mm. Other top fi nishes on a base of fl uorocarbonpolymers, e.g. PVDF, PVF or FEP, are applied within a range of 1.0–1.5 mm. If the top layer is applied as a foil, e.g. 0.03 mm PVF foil, it will give better protection than would a top coat applied in liquid form, because the surface will be more effectively sealed against environmental impact. If weldable textiles or foils are welded together, the non-weldable top coats have to be removed from the welding area. If not done properly, this already critical zone is left partly unprotected.

2.6 Combining optimised materials to form

buildtech composite materials

In many cases, the desired properties of a buildtech textile can only be achieved through combining a fabric having high tensile strength with a coating. Currently, over 90% of all membrane projects have been realised by just two material combinations: PTFE-coated glass fabric, PVC-coated

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polyester fabric and ETFE foil. The PTFE/glass and PVC/PES systems fulfi l all requirements for weather protection and strength in outdoor use. Nevertheless, silicones, PUR coatings and new fi bre developments (PTFE fi bres, PBO) will provide interesting new membrane systems in the future. Some buildtech composite systems are as follows.

PVC-coated polyester fabric is the oldest established membrane material and has been used since the 1950s. Its properties are well known and a variety of tensile strengths are available for this system, from 2000 N for 5 cm and a weight of 0.6 kg/m2 to 10,000 N for 5 cm at a weight of 1.7 kg/m2. Flame resistant PVC/PTFE fabric with a fl uoropolymer top coat is the usual choice for folding applications. An additional PVF topcoat will provide the best protection against UV radiation for PVC/polyester. Where dyeing is required, a PVC membrane coated with polyester fabric offers the widest range of choices. Because the PVC is brittle at low temperatures, it cannot be installed in an environment which will be permanently cold. It is guaranteed for up to 15 years.

PTFE-coated glass fabric is considerably more expensive than PVC-coated polyester fabric but is the preferred material for high-end applica-tions because of its durability (guaranteed for up to 30 years), non-combustibility and self-cleaning properties. This system is less subject to elongation, and its relative stiffness makes it unsuitable for retractable and deployable membrane constructions because folding and fl exing weakens the fi breglass fabric. Dyeing the membrane is not easy, because most colour systems will be affected by the high processing temperatures (>320°C) when the PTFE is sintered on the glass fabric. After 10–12 sinter-ing cycles, the surface is closed by a FEP fi nish. Tensile strengths range from 1000 N for 5 cm length at a weight of 0.4 kg/m2 to 8000 N for 5 cm at a weight of 1.6 kg/m2. Translucency can be up to 25%. Translucency, low-e properties and sound-damping capabilities may also be adjusted by the weight of the fabric and the setting of the weave. Figure. 2.10 shows such a PTFE-coated glass fabric having 10% translucency, a low-e value of 0.4 and 70% sound-damping capabilities.

Fluoropolymer-coated glass fabric is a new system with adjustable trans-lucency up to 50% and a high tensile strength.

PTFE-coated high tensile PTFE fabric (e.g. 4000 N for 5 cm), preferably coated on both sides, will give the best results regarding environmental stability and foldability, but is very expensive.

Silicone coated glass fabric has good fl ame-retardant properties, releases little smoke, leaves no toxic combustion products and is more weather resistant than PVC. However, its self-cleaning effect is inferior to that of PTFE. Silicone is more fl exible and protects the glass fabric better than PTFE and has very good translucency, because the refraction indices of fi breglass and silicone are similar.

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PUR-coated light polyester fabric with a fl ame-retardant fi nish may be welded and is used in helium balloons and airships.

PTFE fabric with high transparency is treated with a special coating to enhance welding properties and watertightness.

PCV-coated aramid fabric is the strongest available membrane material and is typically used for high pressure air beam tubes which function as primary structures. PVC protects the aramid against UV radiation. Because there is no translucency, its application is limited to high load applications.

THV-coated ETFE and THV-coated PTFE have the highest transparen-cies and the overall fl uoric polymer systems are highly stable against envi-ronmental infl uences for up to 30 years. Figure 2.11 shows a coated ETFE foil on which a regular pattern of dots has been printed to reduce transpar-ency and heat fl ux.

An overview of the membrane properties is given in Table 2.3. It should be pointed out that largely mean values are presented, as data acquisition is diffi cult and measured values are diffi cult to collate.

2.7 Primary structures for building and construction

The discussion of primary structures is not the main topic of this chapter; therefore only a short overview is provided. A roof system consists of the primary structure which has to carry all loads and must be stable in itself without depending upon the membrane. The primary structure forms the

2.10 PTFE-coated glass fabric with 10% translucency, 0.4 low-e, 70% sound damping capabilities.

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connection to the ground or to the surrounding buildings and consists of straight or curved masts supported by steel ropes. It is usually made with cast steel, stainless steel, gluelam timber constructions or reinforced concrete.

Fibre-reinforced composite materials are relatively new and are of interest for primary constructions. These materials are lightweight and may easily be processed into complex forms. In specifi cally designed primary constructions, the natural forms of organic membranes may have a counterpart in bionic development such as the ‘technical plant stem’, which is formed on a model of giant reeds and horsetail (Milwich et al. 2006).

2.8 Future trends

2.8.1 R&D fi bres

Nanotechnology

Nanotechnology has improved the technical properties of fi bres in textiles and coatings in such areas as electrical conductivity, magnetic susceptibil-ity, interaction with light, photonics, chemical protection, friction control, abrasion resistance, waste water and oil repellence, soil release and bio-compatibility. Tailoring and controlling structures on the nano-scale level is a key factor in the development of advanced materials or structural components in multifunctional applications. Some fi nishing processes in

2.11 ETFE foil with printed-on pattern to reduce transparency and heat fl ux.

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Table 2.3 Overview of buildtech membrane properties

Material and textile construction Coating (+ fi nish) Area weight DIN 55352

Tensile strength warp/weft

Fire resistance DIN 4102

Trans- lucency

Light refl ection

(g/m2) (N/5 cm) DIN 53354 (N/mm2) EN ISO 527-1

(%) (%)

Polyester woven fabric: PVC coating 600 2000 B1 0–25 50–70 Type 1 800 3000/3000 Type 2 900 4400/4000 Type 3 1050 5750/5100 Type 4 1300 7450/6400 Type 5 1450 9800/8300Polyester woven fabric PVC + aryl fi nish B1 0–25 50–70

PVC + PVF fi nishPVC + PVDF fi nish

High strength polyester woven fabric 400 4000 B1 30–35 60–70Glass fi bre woven fabric PTFE coating 400 1000 A2 4–22 (30) 65–75

800 35001150 58001270 66001550 7500

Glass fi bre woven fabric Silicone coating 800 3500/3500 A2 10–20 (30) 50–701270 6600/6000

Glass fi bre woven fabric Fluorine polymer coating

300 3250 A2 10 59

Open mesh glass fi bre woven fabric PTFE coating 300–800 450–5000 A2 <95

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Open mesh glass fi bre woven fabric PTFE fi lm lamination 700–1200 2500–5000 A2 35–65 10–20Open mesh glass fi bre woven fabric PVC coating 500–1000 1500–5000 B1 <20 20–40Multifi lament PTFE woven fabric 300 2390/2210 A2 15–40 (72) 50–70

520 3300/3400710 4450/4500

Monofi lament PTFE woven fabric 300–600 400–1000 A2 <90 <50Woven fabric from ETFE yarns THV coating 250 1200/1200 B1 <90Stainless steel woven fabric 3000–12000 2000–30000 A2 <95Aramid woven fabric PVC 900 7000/9000 B1 –

2020 24500/24500Cotton/polyester blend woven fabric 350 1700/1000 B2 5–10

520 2500/2000PVC foil 200–2000 300–2000 B1 <90 <60Fluorine polymer foil 50–2000 300–600 B1 <96 <60ETFE foil: 50 μm 88 64/56 N/mm2

80 μm 140 58/54 N/mm2

100 μm 175 58/57 N/mm2

150 μm 262 58/57 N/mm2

200 μm 350 52/52 N/mm2

250 μm 435 40/40 N/mm2

THV foil: 500 μm 980 22/21 N/mm2

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Material and textile construction Coating (+ fi nish) Dirt repellence Life expectancy (years)

Flexing durability

Applications/remarks

Polyester woven fabric, types 1–5 PVC coating Suffi cient 10–15 Good Standard materialPolyester woven fabric PVC + Aryl fi nish Good <20 Good Enhanced self-cleaning ability,

higher life expectancyPVC + PVF fi nish Very goodPVC + PVDF fi nish Very good

High strength polyester woven fabric Good 10–20 Good Translucent noise controlling fabric for interior architecture

Glass fi bre woven fabric PTFE coating Very good 25–30 Poor Material for high end use, making up is demanding

Glass fi bre woven fabric Silicon coating Good 25–30 Poor Poor self-cleaning abilityGlass fi bre woven fabric Fluorine polymer

coatingGood 15–20 Poor Noise control fabric with low-e

value <0.4Open mesh glass fi bre woven fabric PTFE coating Very good <25 Poor Different pore sizesOpen mesh glass fi bre woven fabric PTFE fi lm

laminationVery good <25 Poor Well-balanced ratio of tensile

strength and translucencyOpen mesh glass fi bre woven fabric PVC coating Good 10–15 Poor All-purpose material, e.g. shadingMultifi lament PTFE woven fabric Very good <25 Very good Extreme high end use, especially

suited for folding membranesMonofi lament PTFEwoven fabric Very good <25 Very good Extreme high end use with high

translucencyWoven fabric from ETFE yarns THV coating <25 Very good Only small span length possible,

only indoorsStainless steel woven fabric Good <50 Poor Special design, air ventilationAramid woven fabric PVC coating Poor <20 Good Heavy duty application, low

elasticity, low translucencyCotton/polyester blend woven fabric Poor <5 Very good Indoor application, less stressed,

temporal usePVC foil 15–20 Poor Only indoor use possibleFluorine polymer foil/ETFE foil

50–250 μm THV foil, 500 μmVery good <25 Poor High end use materials for

pneumatic cushions

Table 2.3 Continued

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textile production may already be considered as nano-coating applications. In future, by reducing the diameter of a fi bre, it may be possible to reduce the thickness of a coating to as little as 10 nm.

The effective methods currently available for separating agglomerations will promote the application of nano-fi llers such as nano-clay. Because the dimensions of these particles are smaller than the wavelength of light, there is a marked reduction in light scattering, thus enhancing transparency.

Further research work on nanotechnology has the following aims:

• Reduction of the fi bre diameters down to 2–100 nm, e.g. for optical effects

• Creation of nano-structures in the body of a material by use of nano-fi llers (e.g. pigments, TiO2, ZnO, clay)

• Chemical or topographical modifi cation of the fi bre surface (e.g. profi l-ing fi bres)

• Deployment of phase separation technology and the promotion of self-organising monolayers.

FEM calculation

Improved calculation tools, notably fi nite element modelling, will bring about advances in building with textiles. An example of such FEM model-ling is shown in Fig. 2.12 which is a single-fi bre modelling approach devel-oped by ITV Denkendorf.

2.8.2 R&D coatings

Sol-gel techniques

Sol-gel technology offers many possibilities for textile functions and fi nish-ing. Nano-sol dispersions consisting of organic and inorganic materials may

2.12 FEM calculation with a single-fi bre modelling approach developed by ITV Denkendorf.

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be applied by means of textile and sol-gel processes to yield a specifi cally functional fi lm on the fi bre. For example, the incorporation of highly fl uo-rinated silane compounds form oleophobic dirt-repellent layers and the incorporation of ammonia compounds will produce antistatic layers.

Metallisation and layers with ceramics

In a physical vapour deposition (PVD) process, atoms or molecules are vaporised and subsequently condense on a substrate as a solid fi lm. Cathodic sputtering is the favoured technology for applying metal coatings to textiles. This technology offers considerable additional potential, not only for the creation of metallic fi lms but also for ceramic fi lms. Thermal spraying is an alternative technology which has also proved suitable for the ceramic coating of textiles.

Polymer coating by atmospheric plasma

Research work is being carried out on plasma processes for polymeric coatings under atmospheric pressure. Plasma-based modifi cations are dry processes and therefore offer an interesting economical alternative to traditional wet textile fi nishing systems. Atmospheric pressure plasma systems may easily be integrated into continuously running textile produc-tion and fi nishing lines. Cold or low-temperature plasma requires control of the energy supply to keep the gas at room temperature. The plasma treatment process is applicable to nearly all kinds of fi bres, the advantages being:

• The surface properties are modifi ed without changing the properties of the fi bre bulk nor its friction coeffi cient, surface energy or antistatic behaviour.

• It is a water-free process, eliminates energy-intensive drying processes and minimises the use of chemicals and production of waste water.

• It increases adhesion, lamination, coating and taping by up to 100%.• It enhances the wetting of yarn by liquid coating systems.• It changes water absorbency, hydrophobicity and oleophobicity at dif-

ferent levels.

Encapsulated plasma devices are necessary for the plasma polymerisa-tion processes. A continuous process, however, is still possible if there is a simple gas-lock at the air inlet of the reactor chamber. The production of water- and oil-repellent layers on textiles by plasma polymerisation using fl uorocarbon gases during the continuous process is already possible (Stegmaier et al. 2004). The structures produced by chemically deposited

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fl uorocarbon layers with plasma are characterised by a relatively high degree of cross-linking.

The use of aerosols in plasma technology increases the available spec-trum of suitable chemicals considerably. To a certain extent, liquid chemi-cals, solutions and dispersions can be used in plasma for surface modifi cation with the help of aerosols under atmospheric pressure. Combinations of aerosols and spraying application in dielectrical barrier discharge for the surface treatment of textiles is in the fi rst stage of development and offers potential for future development. Examples of current and future applica-tions are:

• Physical surface modifi cation, e.g. creation of electret properties on fi lters

• Chemical functionalisation• Chemical and topographical nano-structuring.

2.8.3 Nanotechnology

A natural example of hydrophobic and nano/micro-scaled structured sur-faces may be observed in lotus plants. These minimise the area of contact to water and dirt particles and constitute extremely high contact angles, allowing water droplets to roll off at the slightest inclination. When rolling off, the water droplets remove dirt particles lying loosely on the surface, leaving a clean and dry surface behind. This process is called the ‘Lotus-effect®’. When applied to textiles, the term refers to the self-cleaning capa-bility of a surface by water (e.g. rain) without the addition of cleaning agents or mechanical infl uences. It offers potential for several applications, including such outdoor use as textile roofs for airports and railway stations or solar protection materials.

2.8.4 Smart materials

In the future, smart materials will be introduced into textile architecture as actuators and sensors or for communication purposes. The properties of these materials are not fi xed and they will have the capacity to adjust their stiffness, position, vibration frequency and conductivity in response to envi-ronmental changes such as temperature or humidity. They consist of shape-memory alloys or polymers, piezo-ceramics, magneto-restrictive alloys and electro or magnetic rheological fl uids. A future challenge will be the fi xing of functional materials not only to the surface of a textile but also by embedding the function directly into the textile or even into the fi bre itself, possibly by means of bicomponent spinning.

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2.9 References and bibliography

Journal: Bauen mit Textilien, journal, Ernst & Sohn, Berlin (1999–2001)Bögner-Balz, H., Zanelli, A. Ephemeral architecture time and textiles, Proceedings

of the Tensinet Symposium 2007, 16–18. April, Milan, Italy (2007)Denkendorfer Fasertafel of ITV Denkendorf, GermanyHearle, J.W.S. High-performance Fibres, Woodhead Publishing, Cambridge (2002)Knecht, P. (ed.) Funktionstextilien: High-Tech-Produkte bei Bekleidung und

Heimtextilien; Grundlagen, Vermarktungskonzepte, Verkaufsargumente, Deutscher Fachverlag, Frankfurt/Main (2003)

Koch, K.-M. Bauen mit Membranen, Prestel Verlag, Munich, Germany (2004)Koslowski, H.J. Dictionary of Man-Made Fibres, International Business Press,

Frankfurt/Main (1998)Milwich, M., Speck, T., Speck, O., Stegmaier T., Planck, H., Biomimetics and techni-

cal textiles: Solving engineering problems with the help of nature’s wisdom, American Journal of Botany, Vol. 93, No. 10 (2006)

Onate, E., Kröplin, B. Textile composites and infl atable structures II, Proceedings of the II International Conference on Textile Composites and Infl atable Structures, 2–5. October, Stuttgart, CIMNE Barcelona (2005)

Onate, E., Kröplin, B. Textile composites and infl atable structures III, Proceedings of the III International Conference on Textile Composites and Infl atable Structures, 17–19 September, Barcelona, CIMNE (2007)

Schneider, P. Using coatings to give materials new properties, ITB International Textile Bulletin, No. 1 (2004)

Stegmaier, T. High-performance and high-functional fi bres and textiles, in Textiles in Sports, editor R. Shishoo, CRC Press, Boca Ration, FL (2005)

Stegmaier, T., Dauner, M., Dinkelmann, A., Scherrieble, A., Schneider, P., Planck, H. Nanostructered fi bres and coatings for technical textiles, Technical Textiles, No. 4 (2004)

www.cirfs.org, Comité International de la Rayonne et des Fibres Synthétiques, European Fibre Association, Brussels

www.fi bersource.com, American Fiber Manufacturers Association, Arlington, VAwww.ivc-ev.de, German Fibre Association, Frankfurt/Main, Germany

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49

3Technical characteristics and requirements of

textiles used for building and construction

B. BAIER, University of Duisburg-Essen, Germany

Abstract: Lightweight buildings that save on materials and energy, e.g., those using textiles, can meet most modern-day requirements. This chapter deals with the main types of textiles used for building construction and their incorporation into building materials, including discussions on structural membranes, the fabrication of material components, and their handling, production, application and capability. Some sections show the standards for their selection on the basis of properties such as mechanical strength, cost, fl exibility, processability, durability and resistance to UV light, humidity and chemical attacks or other fouling behaviour, cleaning behaviour and fi re resistance, besides their ecological and environmental aspects.

Key words: lightweight construction, textile building materials, structural behaviour, physical characteristics.

3.1 Introduction

Over the last few decades, more and more attempts have been made to create buildings that are both economical and environmentally friendly by using new materials and special construction methods. ‘Lightweight’ con-structions, for example those made of textiles, can meet most modern-day requirements. In the building sector, therefore, the term ‘lightweight con-struction’ is used to describe particular methods for increasing economic effi ciency, which can reduce the weight of building constructions together with costs and work time by the use of special building materials, methods and structural forms. In civil engineering, these are summarized as ‘mem-branes’ – thin, predominantly tension-stressed construction units, for example textile-strengthened planar formations consisting of plastic plus sheet metals or foils from metal or plastics.

Today, the range of applications for membrane constructions extend from the simple camping tent for short-term residential use, through to temporary or improvised accommodation for disaster-affected people, ref-ugees or pilgrims, up to highly technical mobile, temporary or durable shelters, and adaptable or large-span constructions for storage and produc-tion, exhibitions, meetings and cultural or sports events.

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In addition, net-like fabrics made from plastic or steel are used for bird or animal enclosures, and foil-coated fabrics are used for protective covers, facade components or rooftops. The possibilities for the use of membranes are not limited to structural engineering above ground; they are also suit-able for use in foundation engineering, the linings of clarifying and storage basins, the sealing of dumps, environmental protection, and offshore tech-nology. Already in production, their outstanding, controllable mechanical characteristics and their relatively good stability against chemical attack make modern artifi cial fi bres, plastic fabrics and membranes also suitable for laminates or as reinforcement in wood or concrete composite structures. Many encouraging examples suggest that their present range of applica-tions will substantially increase.

Former arguments against the use of textile membranes with respect to their durability, thermal insulation and soundproofi ng are no longer valid today, as these issues can be addressed by using the latest appropriate materials with the application of most modern construction techniques.

3.2 Historical development of fabrics used for

construction

For early humans, with their nomadic way of life, nest-like shelters were the optimal design, originally made of furs or skins, and later from layers or fabrics of vegetable or animal wool fi bres. The tent, with its small car-rying size, was easy to transport, to erect and to dismantle rapidly and to adapt without much effort to the most diverse climatic requirements. For thousands of years, tents were the most widespread dwellings, but when humans changed to a more settled and permanent way of life, these light constructions were replaced with fi xed, heavy and thus usually more durable buildings. It took centuries to develop a new architecture and with it a change from the original manual construction to our modern industrialized building methods. Building materials have themselves improved over the centuries in the course of development and have been adapted to today’s requirements and the different functions they have to perform.

In recent decades, therefore, work in the construction industry not only increased the development and improvement of constructions from the proven materials of wood, steel, concrete and glass, but also the advance-ment of new materials like plastics, which turned out to be particularly suitable materials for lightweight building and for the economic covering of spacious, support-free areas.

The high quality and durability of today’s membrane building materials enable the construction of covered surfaces or free spans in orders of mag-nitude which are limited in practice only by the construction costs. Constructional membranes can create structures which are hard to achieve

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Technical characteristics and requirements of textiles 51


with other building methods. In conjunction with arched steel-tube sup-ports or cable-net reinforcement, membrane structures can cover spans of several hundred metres in diameter using relatively small quantities of material, and with pneumatic support can theoretically cover up to several kilometres.

3.2.1 Fabrics from natural fi bres

In biological structures, the production of thread constructions is geneti-cally programmed in some plants or in organisms such as spiders or cater-pillars. Compared to these, the production of technical textile planar formations is a relatively late achievement in the history of the develop-ment of mankind since the Neolithic Age. The oldest tent-like constructions consisted of grass, sheets, skins, furs or woollen hair felts. Fabrics for con-structions like tents were originally made from threads of sheep wool, goat or camel hair, and for more than 5000 years have been made from vegetable fi bres such as fl ax or hemp. By the end of the sixteenth century, cotton was being cultivated throughout the warmer regions in Asia and the Americas, and since that time the majority of textiles for clothing and construction have been made from cotton. After the invention of the spindle and loom, fabrics could fi nally be manufactured by technical procedures and on a greater scale.

The yarns made from natural fi laments had substantially fewer technical properties compared with today’s synthetic products, were heavy and absorbed substantially more moisture despite being impregnated with water repellant, which also affected the life span. Textiles made from natural fi bre yarns were susceptible to mould attack and rot, got dirty rapidly and were highly fl ammable unless impregnated with special fi re retardants. With increasing demands on the durability and mechanical strength of fabrics for use in construction, the fabrication of natural fi bres for use in this sector has declined over the last few decades.

3.2.2 Fabrics from synthetic fi bres

Finally, with the discovery of nylon in 1938, the fi rst fully synthetic fi brous materials became available. Polyester, discovered in 1947, was also an important industrially manufactured synthetic fi bre for use in construction. At this time, with the progressive development of other new synthetic plastic fi bres and fi bre products, methods began to change from small-scale manufacturing that was associated with craftsmanship to today’s apparently boundless scale of industrial production of textile building materials. Until the mid-1970s, the production curve for technical mass plastics doubled every fi ve years, then fl attened out and fell for a short time.

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In the year 2000, according to UN data, the 15 largest manufacturing countries produced over 28.2 million tons of artifi cial fi bres based on cel-lulose and synthetics. Germany was the eighth largest producer with 0.9 million tons. The world production of chemical fi bres continued to increase to approximately 30 million tons by 2002. The increase was predominantly for the production of synthetic fi bres, which make up approximately 93% of all artifi cial fi bres (see Fig. 3.1).

Technical planar formations consisting predominantly of fi bres, fi bre bundles or yarns, which are manufactured by the spinning of two or more threads, are generally designated as either fabrics or textiles. These can be differentiated by their use in non-woven layers of fi bres or threads, mesh networks, or knitted or woven fabrics.

The current concentration on the use of synthetic instead of natural fi brous materials stems from the desire to standardize the physical and mechanical characteristics of materials and to adapt them to the demands of the technical designers and users of membrane constructions. Above all, characteristics such as mechanical fi rmness, fl exibility, workability, durabil-ity, resistance to UV radiation and chemicals, dirt resistance and cleaning behaviour, fl ammability, moisture stability and environmental compatibil-ity determine the costs and therefore the choice of materials.

3.2.3 Composition of fabric elements

Yarns or threads which are currently used for textile building are made predominantly of polyester (PES), with a small but increasing amount

3.1 World production of artifi cial fi bres.

0

5

10

15

20

25

30M

illio

n tons

1994

1999

2000

2002

Germany

Eastern Asia

Others

World

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of fl uoropolymers such as PTFE, for example GoreTM Tenara® (ref. Gore), or most recently of E-glass fi bres. The majority of the fabrics currently available fulfi l the highest requirements of mechanical fi rmness, combustibility, UV-radiation stability and chemical resistance. Other fi la-ment materials developed quite recently such as aramid PP, for example Kevlar® (ref. DuPont), or carbon fi bres (CF) have outstanding charac-teristics which also make them suitable for use in building. However, they are only employed in small amounts for special tasks because of their high cost.

Fabrics generally consist of two-thread warp and weft systems. The indi-vidual threads are crossed in a certain kind of weave, usually at right-angles to one another in so-called cross-weaving. The most important basic weav-ings are ‘plain’ or ‘canvas’ (also called ‘tabby’, ‘linen’ or ‘taffeta’ weaving) and ‘atlas’ weaving (also called ‘satin’ or ‘twill’ weaving). Today, most fabrics used for textile buildings are preferably made by either ‘linen’ weaving, or ‘panama’ (‘basket’) weaving, which is similar to the linen weave but with from two-by-two up to four-by-four warp and/or weft threads (see Figs 3.2, 3.3 and 3.4, ref. Wiki).

3.2 Plain/canvas/linen/tabby weaving: detail of a diagram of the structure of a balanced plain weave textile (source: Wikimedia Commons, fi le: Tabby1sm.png, author: Jauncourt).

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3.3 Atlas/satin/twill weaving: detail of a diagram of the structure of a balanced 2/2 twill textile (source: Wikimedia Commons, fi le: 22twillsm.png, author: Jauncourt).

3.4 Basket/panama weaving: detail of a diagram of the structure of a balanced ‘basketweave’ textile (source: Wikimedia Commons, fi le: Basketsm.png, author: Jauncourt).

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3.3 Overview of textile materials currently

used for construction

In today’s building industry, the most frequently used structural mem-branes are coated on both sides. Occasionally they are coated just on one side, and uncoated fabrics or foils with yarn reinforcements are also avail-able that are specially adapted to particular applications.

PVC-coated polyester fabrics are used as the building materials for the majority of membrane constructions. In certain cases, fabrics and yarn reinforcements made of polyester require special protection against UV radiation. Because of the need for lower water and/or dirt absorption at the edge of polyester fabrics, specially treated ‘low wick’ yarns are used to avoid the unwanted wick effect (see Fig. 3.5, ref. Mehler).

Nowadays, PVC-coated, high-quality, low-wick treated polyester fabrics with warranties of 10 years and a structural lifespan of more than 20 years are preferred for use as the membranes of tension structures. The PVC coatings mostly contain plasticizers, UV stabilizers, fi re retardants, colour-ing and fungicidal additives. Topcoats of acrylic lacquers are mostly used

3.5 (a) Not ‘low-wick’ prepared weaving; (b) specially prepared ‘low-wick’ weaving (source: Mehler Texnologies, copyright permitted).

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to improve the longevity of the coatings, but lacquers of fl uorinated poly-mers like PVDF are also used, for example VALMEX® MEHATOP (ref. Mehler), which produce a long-lasting self-cleaning effect for the PVC membrane surface in combination with perfect welding characteristics, without the complication of grinding the PVDF lacquer off the membrane edges (see Fig. 3.6, ref. Mehler).

In special cases that have some other requirements, fl uoropolymer-coated or silicone-coated fi breglass fabrics are increasingly being used. These materials are preferred mainly for foils and coatings and topcoats of fabrics, due to their thermal and chemical stability as well as their good self-cleaning properties.

Membrane materials usually get selected for building construction on the basis of properties such as mechanical strength, cost, fl exibility, process-ability, cleaning behaviour, durability and resistance to UV light, fi re, humidity and chemical attacks or other fouling behaviour, besides their ecological and environmental effects.

3.3.1 Uncoated fabrics

Polyester fabrics

Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many types of polyester, the term ‘polyester’ as a specifi c material most commonly refers to polyethylene terephthalate (PET). It is produced in numerous forms such as sheets and three-dimensional shapes and also as granulates.

Polyester is a thermoplastic material and is able to change its shape after the application of heat. Therefore PET granulate is the base material for polyester fi laments that are converted to yarns for the production of fabrics. This polyester (known as PES in textile production terminology) is, without

3.6 (a) Polyester base fabric; (b) with PVC coating and (c) PVDF topcoat.

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special treatments, combustible at high temperatures and generally needs a tinted coating for outdoor use because of its low UV resistance. PES tends to shrink near fl ames, but is self-extinguishing upon ignition. PES fi bres have a high tenacity and E-modulus as well as low water absorption and minimal shrinkage in comparison with other industrial fi bres.

Fibreglass fabrics

Glass is essentially produced by mixing sand and stone components from quartz (SiO2), limestone or dolomite (CaO and MgO), alumina (Al2O3), soda, potash and boron compounds, molten at 1600°C. The liquid glass is pumped through micro-fi ne nozzles and cooled to obtain fi laments with a diameter of 5–24 μm. The fi laments will lead to a contorted thread or to a roving, which is loosely connected and covered with a fi nish that links the fi laments together and protects the glass against wear and tear.

By using variations of the ‘recipe’, different types of glass can be pro-duced. Structural reinforcement threads used for building construction ele-ments are mostly made from so-called E-glass (electrical). It has good electrical properties, a low alkali content, good tensile strength, low elonga-tion at rupture and relatively low costs, but has poor fl exibility without special treatments. E-glass is the most widely used material for membrane fabrics and reinforcement in composites, but is not practical for fabrics in membrane structures that need to fold and unfold frequently.

Uncoated fi breglass fabrics are not, without special treatment, suffi ciently resistant to UV radiation and the deposition of dirt. Efforts are being made to reduce these disadvantages with coatings of PTFE or silicone, which will be discussed in later sections.

Fluoropolymer fabrics

Polytetrafl uoroethylene (PTFE) is a fully fl uorinated polymer, which was discovered by chance in 1938 by Roy Plunkett. Later, the polymerization process was initiated at high pressure with peroxide. In 1941, DuPont received the patent on PTFE, therefore it is often denoted colloquially by Tefl on®, the original trade name of DuPont PTFE (ref. DuPont). Other examples of PTFE trade names used by manufacturers are PTFE DyneonTM, formerly Hostafl on (ref. Dyneon), and Gore-Tex® (ref. Gore).

There are fabrics made of 100% high-strength expanded PTFE fi bres that are extremely useful in the building sector. Fluoropolymer fabrics are naturally stain resistant and easy to clean and have an expected lifetime of around 25 years with 15 years’ full warranty. The fabric elements have to be sewn together or joined by means of special fl uoropolymer adhesive foils. These architectural fabrics combine exceptional textile qualities with

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unlimited fl exibility, fold compactly into a small storage space, and are suitable for interior and exterior retractable and permanent structures, utilizing a wide variety of structural techniques. They are completely immune to UV sunlight, chemicals and pollution, endure extreme tempera-tures and display outstanding fl ammability properties. Their light transmis-sion is approximately 30%, white fabrics stay white, and colours stay true. Prepared materials are recyclable but not eco-degradable. These fabrics are available, according to the data declaration of the producer, for example of GoreTM TENARA® (ref. Gore), in two different standard weights (P/N VG0180-twill, 520 g/m2 or 15.4 oz/yd2 and P/N VG0181-twill, 330 g/m2 or 9.75 oz/yd2).

3.3.2 Coated fabrics, coatings and topcoats

PVC coatings

The coatings are usually placed on both sides of the fabric by laminating, rolling or brushing. This is to protect the fabric against the effects of the weather, UV radiation and chemical attacks. Therefore, besides plasticiz-ers, PVC coatings contain, amongst other things, additives such as UV stabilizers, fl ame retardants, fungicidal agents and colours.

Since, despite its water-repelling characteristic, a PVC coating is very susceptible to electrostatically or chemically caused surface contamination, ‘topcoats’ are also applied on the membrane surfaces, in the form of either cover-up foils or a rolled-on coating based on acryl, PU or fl uorine poly-mers like PVDF (ref. Mehler).

Together with criteria such as welding behaviour, dirt resistance, cleaning behaviour and fi re resistance, coatings with the appropriate topcoats play a large role in determining the product’s warranty and/or liability. For membrane materials made from PVC/PES, warranties of up to 10 years are generally given by the manufacturers, but these can be increased by special agreement. PVC coatings with topcoats of fl uorine polymers have a life expectancy of more than 20 years (see Fig. 3.7).

For some years, there have been efforts to replace most ecologically problematic plastics, such as PVC with its undisputed superior economic advantages, in fabric coatings by other plastics with smaller environmental disadvantages. Alternative coatings from fl uorine polymers are being developed, such as PVDF or polyolefi ns on specially treated polyester fabrics. The test results are encouraging, since they seem to be heading in the right direction.

However, the material properties achieved so far for newly developed coatings, with regard to their workability, scratching fi rmness, tear strength of the base fabric and costs, do not as yet compare satisfactorily with the

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properties of well-known PVC coatings. For now, PVC cannot easily be replaced, but it seems that in the future the complete replacement of PVC as a membrane coating material is probably achievable.

Fluoropolymer coatings

For areas with special application requirements, specifi cally modifi ed poly-ester fabrics, as well as fabrics from aramid fi bres, fl uorine polymers and arylamides like Kevlar® (ref. DuPont), have proved to be satisfactory. The membranes show different characteristics depending on the coatings used. Fluorine polymers such as PVDF (polyvinylidene fl uoride) are used on PES fabrics (refs Mehler and Ferrari); a PTFE (polytetrafl uoroethylene) coating is very suitable for fi breglass fabrics (ref. Verseidag); and there is a newly developed composite membrane with THV (ref. Dyneon), a polymeric blend of tetrafl uoroethylene, hexafl uoropropylene and vinylidenefl uorine, used as a coating on PES fabrics, of which VALMEX® vivax (ref. Mehler) is one example.

When there are requirements for particularly high resistance to UV radiation, temperature, fi re or chemicals, the use of fi breglass fabrics with double-sided PTFE coating (glass/PTFE) is preferred (see Fig. 3.8, ref. Verseidag). PTFE-coated fi breglass fabrics are classifi ed according to their tensile strength and their weight per unit area in up to fi ve type classes (see Table 3.1). By today’s standards they will last for more than 40 years; however, they are also up to 10 times more expensive than PVC-coated polyester fabrics with the same tear strength. The colour of the PTFE coating is always off-white, becoming almost white with UV exposure. The light transmission of PTFE-coated glass-fi bre fabrics depends on the thick-ness of the coating, and is approximately up to 20% (ref. Moritz). For a few special applications, the use of PUR (polyurethane) and polyolefi n coatings on corresponding fabrics has also been suggested.

Topcoat with primer

Topcoat with primer

Polyester base fabric

PVC coating

PVC coating

Prime coating

Prime coating

3.7 Typical section of PVC-coated polyester fabric with topcoat.

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Table 3.1 Technical characteristics of selected fabrics and foils

Fabric/coating foils Quality type thickness

Weight (g/m2)

Tensile strength (N/50 mm), warp/weft

Elongation at rupture (%), warp/weft

Polyester/PVC-coating Type I 600–800 3000/3000 15/20Type II 900 4400/4000 15/20Type III 1100 5750/5200 15/25Type IV 1300 7400/6400 15/25Type V 1450 9800/8300 15/25

Fibreglass/PTFE-coating Type I 800 3500/3000 3–12Type II 1050 5000/4400 3–12Type III 1250 6900/5900 3–12Type IV 1500 7300/6500 3–12

PTFE-fabric non-coated 300–800 3880/3500 30–40

ETFE foils 50 μm 87.5 64/56 N/mm2 450–500 80 μm 140 58/54 N/mm2 500–600100 μm 175 58/57 N/mm2 550–600150 μm 262.5 58/57 N/mm2 600–650200 μm 350 52/52 N/mm2 600

Source: Baier 2004.

3.8 PTFE-coated fi breglass membrane.

Silicone coatings

The synthetic polymer silicone was originally produced for use as a sealant or bonding agent. It is an elastomere, which is chemically inert, not degrad-able by UV light and thermally stable. The rapidly expanding market for construction membranes encouraged the increasing use of silicone for coating glass-fi bre fabrics. The combination of a high-strength, fl exible glass fabric with a good fi re-retardant, non-toxic, emission-free coating and a soil-repellent topcoat is suitable for producing fl exible, durable lightweight membrane structures, which are available in any colour. Silicone-coated

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membranes can be joined or seamed with special silicone adhesive tapes by applying heat and pressure to the seam. Silicone-coated glass-fi bre fabrics, for example PD Interglas Atex® (ref. Atex; see Fig. 3.9), are easy to clean, display up to 40% translucency (depending on the type of fabric and thickness of the coating) and have an expected lifespan of more than 25 years.

3.3.3 Net-like fabrics

For building structures, a wide range of different transparent or translucent foils are available, which are reinforced with rectangular or differently shaped nets. PVC-laminated PES mesh fabrics are available for interior use, e.g. POLYMAR® (ref. Mehler; see Fig. 3.10); however, when specially treated for protection against UV radiation, like dyeing polyester net yarns, PVC-laminated PES mesh fabrics are also very suitable and long-lasting enough for exterior applications.

Much more expensive, but similarly long-lasting and with very good resistance to dirt contamination, UV radiation and chemical attacks, are fl uoropolymer foils with reinforcement nets made of glass fi bres (refs

3.9 Silicone-coated fi breglass membrane.

3.10 PVC-laminated PES mesh fabric.

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3.11 Fluoropolymer foil with glass-fi bre reinforcement net.

Verseidag and formTL; see Fig. 3.11). With comparable characteristics, there are the recently developed polyester nets with THV coating, like VALMEX® vivax (ref. Mehler). They are highly translucent, are available in a wide range of colours and are very well suited to interior use. However, with special UV-protected polyester threads, they are also appropriate for long-lasting exterior applications.

3.4 Technical characteristics and requirements of

fabrics for modern structural engineering

PVC-coated polyester fabrics are generally classifi ed in Europe according to their tensile strength and their weight per unit area, predominantly into fi ve type classes, but in a trial also in up to seven classes (see Table 3.1). According to their fi re behaviour (infl ammable with diffi culty), they are added to the building material class B1 of German Industrial Standard DIN 4102 and they have a prospective life span of approximately 25 years. They can be used not only for long-lasting buildings but also for convertible and foldable structures. PVC/PES membranes are economical, recyclable and available in almost all colours within a wide range of qualities.

Depending on their purpose, PTFE-coated fi breglass membranes have the most diverse technical requirements such as durability and economy, dirt-defl ecting and/or self-cleaning characteristics, moisture stability and fi re resistance. They fulfi l the requirements for building material class A2 (not combustible) according to German Industrial Standard DIN 4102 (see Table 3.1), but are not suitable for structures which are to be folded several times. They are normally only available in white. Silicone-coated fi breglass fabrics can attain the requirements of building material class B1. The

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desired quality criteria of the respective fabrics, for example their colour, mechanical fi rmness and stretch, can be selected from the extensive range on offer or can be created by special order in the pre-production process.

3.4.1 Thermal and acoustic behaviour of fabrics and composite elements

Thermal insulation

Like all lightweight constructions, membrane structures generally react very rapidly to outside energy infl uences due to a lack of thermal mass. The thermal insulation characteristics of single-layer membranes with a mea-sured U-value of 5.7 W/m2K, for example, do not meet the requirements of German Energy Saving Standards (EnEV) for interiors permanently kept at a moderate temperature. Solar radiation, particularly in summer, may cause high temperatures above and below the membrane surfaces as a consequence of the transformation of radiant energy to heat. In closed rooms, this causes the unwanted heating of interior air. But at night or in winter time, low outside temperatures cause the cooling of interior air by thermal radiation. Temperature peaks can usually only be controlled by expending large amounts of energy for mechanical ventilation, cooling and heating. This system-dependent characteristic leads to the conclusion that membrane constructions are most suitable for open roofs or for covered spaces which do not have to be kept permanently at a moderate tempera-ture. However, according to the current energy-technical requirements for closed rooms that must be permanently kept at a moderate temperature, buildings that comply with these can be constructed with membranes by using special constructional or climatic–technical measures. For example, only small technical modifi cations are necessary to meet the requirements on thermal protection according to German Energy Saving Standard EnEV in the summer as well as in the winter time.

Encasing constructions can be used with several membrane layers to form an intermediate space that can be fi lled with air or another insulating material, making U-values from 2.7 to 0.8 W/m2K possible. U-values down to even 0.2 W/m2K can be obtained by using opaque, fl exible mineral fi bre fi lls or translucent insulating material, for example blister foils, as well as refl ecting intermediate layers which are commonly used in space technol-ogy (ref. LPS; see Fig. 3.12).

Energy conservation and energy production

Because of the partial high light permeability of the membrane material, using single-layer foils or textile membranes sometimes proves to be more

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suitable than conventional constructions, since artifi cial lighting is largely unnecessary in covered areas during daylight hours and substantial energy conservation is possible. This can positively affect the total operating energy expenditure of the building.

Developments have also been made that can change the light permeabil-ity of multi-layer membrane constructions by means of mechanically, pneu-matically or electromagnetically changeable elements, by gas fi llings or by injected granulates, depending upon the thickness of the membranes and the wavelength of the light, within the range of over 90% permeability at one extreme up to complete opacity. In addition, by directing airfl ows – actively or passively – under or between the membrane layers, gains from solar energy may positively affect the total energy balance. If thermal energy gains are supplied to a heat exchanger or a thermal memory, this can also contribute to a positive total energy balance and a reduction in operating expenses for the building. The relevant developments have so far not been used in practice beyond the testing stage (ref. Baier, 1998).

Noise and sound control

The sound insulation effi ciency of single-layer membrane materials is limited because of their small weight per unit area, but lately they have been strengthened and inserted into certain applications as sound-proofi ng or sound-directing elements. New developments can therefore take advan-tage of the fl exible absorbing characteristics of heavily coated fabrics, for example in applications such as sound-absorbing partitions for sports facili-ties and music venues. Spacer fabrics fi lled with sand or liquid, multi-layer

3.12 Composite thermal insulation of blister foils and refl ecting layers.

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membrane mats with mineral-wool fi lling, plus suspended micro-perforated foils can also be employed to give protection from the noise of, e.g., airport terminal buildings, discothèques, multi-purpose halls, etc. Multilayer mem-brane structures, for instance those fi lled with substrate, are also very suit-able when installed as barriers around a noise source or beside noisy traffi c routes (ref. Baier, 2004).

Environmental considerations for textiles used in building construction

As part of the discussion on the use of textile construction membranes, it should be made clear what happens at end-of-life for materials used so far for building construction. Thermoplastic membrane components like PVC can be processed after each utilization period under certain conditions and be supplied for reuse in the raw material cycle. Leading European manu-facturers of PVC/PES membranes and roofi ng sheets have united in order to recycle post-consumer waste, disused membranes and PVC materials (ref. Vinyl) in most modern plants with approved thermo-physical proce-dures. The output of this recycling process is then used for new products. An important factor in the operation of these and other environmental raw-material recovery procedures is logistics, which includes the materials being carefully prepared and sorted prior to delivery. The processing plants are potentially able to achieve a turnover of more than one ton per hour (ref. recovinyl).

3.4.2 Draft, design, computation, engineering success

Load bearing and shape fi nding of membranes

Membrane constructions can be subject to tensile stress simply due to the low compressive and bending rigidity of their surfaces. However, plane surfaces are subject to deformation by external loads such as wind or snow. They tend to fl utter or create snow and water traps, which in extreme cases can lead to failure of the construction. The stabilization of plane areas would require an uneconomically high pre-tension. Consequently, design and draft processes for these follow completely different principles than those for rigid supporting structures, which are mainly bending or pressure stressed. The main difference is that form fi nding for mainly tensile-stressed membrane constructions mostly follows self-regulating pro-cedures. This means that the form of the membranes either approaches the form of so-called ‘minimum surfaces’, following physical principles under the condition of similar surface stresses within defi ned continuous edge-elements, or is infl uenced by changing the boundary conditions, or by inserting additional supporting elements (which can be linear, plane or

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supported at certain points) respectively by different surface stress pre-conditions. This allows the creation of either ‘anticlastic’ saddle-shape surfaces or the generation of ‘synclastic’ surfaces for the case when pneu-matic internal pressure is used like a balloon. Supporting media for the stabilization of internal pressure can be air, gas, water or other liquids, and also granulated materials. A completely free invented design shape, because of the deviation from the ‘minimal form’, requires in general higher efforts for additional supporting elements and in addition creates unneces-sary high costs.

By calculating the stress demands, the construction and dimensioning of the edges, tension elements and anchorages can be determined. A few decades ago, the determination of the form, cutting patterns and precondi-tions for the load-sensitive demands of the surfaces as a basis for the static–dynamic computations were still found simply from a physical model construction, by full-scale transmission of dimensions or simulated defor-mations, and by estimation from practical experience. Today’s engineering successes make use of proven electronic computation methods for the accurate dimensioning of a construction unit and automatic cutting determination.

Assembly, erection and dismantling

The circus tents of the past were erected and dismantled ‘overnight’, almost irrespective of their size. Erection and dismantling were done mainly by hand within a few hours. Today, the ready-for-use manufactured (cut and connected) membrane elements are shipped and transported to the site, then prepared with connection elements such as edge cables, belts, loops and eyes or with clamping plates. The membrane surfaces will be built up in the same way, in anything from a few hours to a few days depending upon their size, by special companies with lifting equipment (cranes, wheeled loaders, fork-lift trucks). After the individual elements have been positioned, they will be attached to edge cables, fi ttings and anchorages, installed between the prepared tie points such as supports, anchor points and foundations, and linked up using the computationally determined forces and measurements. Dismantling takes place very rapidly in the reverse order. The elements either can be repeatedly erected and disman-tled or can be partly reused. They can also be removed after their fi nal use in order to be recycled.

3.5 Future trends

The development of lightweight constructions over the past few years shows that so far only a small fraction of the possibilities for the use

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of plastic foils and textile membranes has been explored. The plastic industry in general, the weavers, coaters and manufacturers of building elements and accessories, and last but not least the technical designers, engineers and architects of membrane buildings (and their trainers) need a deeper understanding and longer experience with these special struc-tures, which differ completely, with regard to their optimal utilization, in many respects from building with substantial, pressure- and bending-stressed materials.

The number of possible solutions to problems of construction with mem-brane building methods corresponds to the variety of available materials and established constructions existing on the market. At the same time, it shows the potential for future developments in this fi eld.

3.6 Sources of further information and advice

Atex: Silicone-coated fi breglass membranes: P-D-Interglas Technologies Ltd (http://www.atex-membranes.com)

DuPont: Fibreglass: E. I. Du Pont de Nemours and Company (http://www2.dupont.com)

Dyneon: Fluoropolymer products (http://solutions.3m.com/wps/portal/3M/en_US/dyneon_fl uoropolymers/)

Ferrari: PVC-coated polyester membranes: Ferrari textiles (http://www.ferrari-textiles.com/)

Gore: Fluoropolymer fabrics: W. L. Gore & Associates, Inc., Gore-tex (http://www.gore.com)

LPS: Lu..po.Therm insulating membrane materials (http://www.lps-gmbh.com)Mehler: Mehler Texnologies membrane materials (http://www.mehler-texnologies.

com)recovinyl: Recycling of vinyl products (http://www.recovinyl.com)Verseidag: PVC-coated polyester, glass/PTFE membranes (http://www.vsindutex.

de)Vinyl: Vinyl 2010 (http://www.vinyl2010)

3.7 References and further reading

Atex: P-D-Interglas Technologies Ltd product data sheets (http://www.atex-membranes.com)

Baier, Bernd: Control of Thermal Energy in Membrane Structures; in: Proceedings of LSA 98, IASS/IEAust/LSAA International Congress on Lightweight Structures in Architecture, Engineering and Construction, Sydney 1998

Baier, Bernd: New approaches and aims in membrane construction; in: Proceedings of the 10th International Symposium for Technical Textiles, Nonwovens and Textile Reinforced Materials, Messe Frankfurt, Frankfurt 1999

Baier, Bernd: Leichtbau mit Membranen – Neue Entwicklungen, Materialien, Konstruktionen; in: Essener Unikate 23, Berichte aus Forschung und Lehre, Ingenieurwissenschaft, pp. 86–97; Universität Duisburg-Essen, Essen 2004

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Baier, Bernd: Particular new aspects of material, construction and design of mem-brane structures; in: Zingoni, Alphose (ed.): Recent Developments in Structural Engineering, Mechanics and Computation, pp. 279–280, Millpress, Rotterdam 2007

DuPont: E. I. Du Pont de Nemours and Company product data sheets (http://www2.dupont.com)

Dyneon: 3M fl uoropolymer products data sheets (http://solutions.3m.com/wps/portal/3M/en_US/dyneon_fl uoropolymers/)

Ferrari: Ferrari SA product data sheets (http://www.ferrari-textiles.com/)formTL: Schmid, Gerd: Bauen mit Membranen, Membran- und Folienwerkstoffe,

Teil 1; in: architektur 3/04, pp. 58–64 (http://www.form-tl.de/)Gore: W. L. Gore & Associates, Inc. product data sheets (http://www.gore.com)LPS: Lu..po.Therm product data sheets (http://www.lps-gmbh.com)Mehler: Mehler Texnologies product data sheets (http://www.mehler-texnologies.

com)Moritz, Karsten: Membranwerkstoffe im Hochbau; in: Detail 6/00, pp. 1050–1058recovinyl: recovinyl product data sheets (http://www.recovinyl.com)Verseidag: Verseidag Indutex product data sheets (http://www.vsindutex.de)Vinyl: Vinyl 2010, vinyl recycling (http://www.vinyl2010)Wiki: Illustrations of textile fabrics by Jauncourt (Wikimedia Commons, fi les

Tabby1sm.png, 22twillsm.png, Basketsm.png)

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69

4Fibre reinforced polymer composite materials

for building and construction

M. MOTAVALLI, C. CZADERSKI, A. SCHUMACHER and D. GSELL, Empa, Switzerland

Abstract: Fibre reinforced polymers (FRPs), a relatively new class of non-corrosive, high-strength, lightweight material, have over the past approximately 15 years emerged as practical materials for a number of structural engineering applications. This chapter introduces constituent materials, FRP composite laminates and multilayer laminate theory, and the durability of composite materials for the construction and building industries, as well as future developments. Furthermore, some of the more common FRP applications in civil engineering structures and design rules are described in detail, including externally bonded FRP plates, sheets and wraps for the strengthening of reinforced concrete, steel, aluminium and timber structural members, FRP bars for the internal reinforcement of concrete, and application of FRP profi les.

Key words: FRP bars, externally strengthening, FRP profi les, confi nement, fl exural strengthening, shear strengthening.

4.1 Introduction

4.1.1 Importance of fi bre composites in structural engineering

The deterioration and functional defi ciency of existing civil infrastructure represents one of the most signifi cant challenges facing countries in the twenty-fi rst century. In the United States, nearly 11% of the nation’s highway bridges are presently structurally defi cient and 19% are function-ally obsolete. In the United Kingdom, over 10,000 concrete bridges need structural attention (Rizkalla and Hassan 2002). A substantial number of structures in Europe are more than 30 years old. Whilst they require con-tinual maintenance, they also require strengthening due to lack of strength, stiffness, ductility and durability (Motavalli and Czaderski 2007).

In addition to deterioration and degradation caused through ageing, weathering of materials, and accidental damage to structures, traffi c and housing/industrial needs have increased dramatically over the past few

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decades with transportation of goods and services being conducted on a global rather than a local basis. There is a need for the widening of highway systems to accommodate greater fl ows of traffi c and for the strengthening of existing structures to carry heavier loads at higher speeds. Enhanced understanding of structural response and natural threats such as earthquakes and storms has led to the establishment of new design codes, and the consequent need to rehabilitate existing structures to ensure their continued safety. Conventional materials such as timber, steel and concrete have a number of advantages, not the least of which is the relatively low cost of the raw materials. However, it is clear that con-ventional materials and technologies, although suitable in some cases, and with a fairly successful history of past usage, lack longevity in some cases, and in others are susceptible to rapid deterioration (see Fig. 4.1), thereby emphasizing the need for better grades of these materials or newer technologies to supplement the conventional ones used (Karbhari and Seible 2000).

Fibre reinforced polymers (FRPs), a relatively new class of non-corrosive, high-strength and lightweight material, have over the past approximately 15 years emerged as practical materials for a number of

4.1 Deterioration of reinforced concrete columns due to corrosion (from ISIS-Canada 2003).

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FRP composite materials for building and construction 71


structural engineering applications. The rapid increase in the use of FRP materials for structural engineering applications that has occurred over the past 15 years can be attributed to continuing reductions in cost, to more comprehensive knowledge of the fundamental properties of composites, which has enabled more specifi c uses and has reduced safety factors to realistic levels, and to the numerous advantages of FRPs as compared with conventional materials such as concrete and steel. Some of the commonly cited advantages of FRP materials over more conventional materials include (ISIS-Canada 2003):

• High strength-to-weight ratios• Outstanding durability in a variety of environments• Ease and speed of installation, fl exibility, and application techniques• Electromagnetic neutrality, which can be important in certain special

structures such as magnetic imaging facilities• The ability to tailor mechanical properties by the appropriate choice

and direction of fi bres• Outstanding fatigue characteristics (carbon FRP)• Low thermal conductivity.

4.1.2 Historical background

FRPs have been used in the automotive and aerospace industries for more than 50 years in applications where their high strength and light weight can be used to great advantage. The history of the use of polymers and com-posites in the construction industry began during the Second World War, when rapid progress was made with the manufacture of the fi rst radomes to house electronic radar equipment. The main growth interest and technol-ogy in glass fi bre/polyester composite in the building and construction industry started in the 1960s (Hollaway 1993). Two major structures were built made of GFRP: the dome structure in Benghazi built in 1968 and the roof structure at Dubai airport built in 1972. By the late 1980s and early 1990s, as the defence market waned, increased importance was placed by fi bre and FRP manufacturers on cost reduction for the continued growth of the FRP industry (Bakis et al. 2002). With the decreasing cost of FRP and the increasing need for infrastructure repair and renewal since the early 1990s, interest in the use of FRP materials for structures has also increased steadily, and there are currently hundreds of fi eld applications of FRPs in structures around the world. The Ibach bridge, located in the Canton of Lucerne in Switzerland, was repaired in 1991 with three CFRP strips, making it the fi rst CFRP reinforced concrete bridge in the world. More in-depth historical background and development overview reports from around the world can be found in Hollaway (1993), Meier (2000), Teng

��



et al. (2002), Bank (2006), GangaRao et al. (2007), and Motavalli and Czaderski (2007).

4.1.3 Chapter contents

The focus in the present discussion is on those FRP materials that are currently used in structural engineering applications. That is, although many different material combinations (combinations of fi bre and matrix) are possible, only a very small sample of the almost infi nite number of pos-sibilities is presented herein. The reader should also keep in mind that several different manufacturing techniques, component shapes and end-use applications are available for FRP materials, but that only those most rel-evant to structural engineering are discussed. More comprehensive discus-sions of FRP materials are available in various composite materials texts: see Eckold (1994), Herakovich (1998), Bank (2006) and GangaRao et al. (2007).

The following sections introduce constituent materials, FRP composite lamina and multilayer laminate theory, durability of composite materials for the construction and building industry, and future developments.

Some of the more common FRP applications in civil engineering struc-tures and design rules are described in detail in the following sections of this chapter, and include:

• Externally bonded FRP plates, sheets and wraps for the strengthening of reinforced concrete, steel, aluminium and timber structural members

• FRP bars for the internal reinforcement of concrete• Application of FRP profi les.

4.2 Constituent materials, material properties

and manufacturing

4.2.1 Raw materials

Fibre reinforced polymer (FRP) composite materials are made of three essential constituents: fi bres, polymers, and additives. In fi brous polymeric composites, fi bres with high strength and high stiffness are embedded in and bonded together by the low modulus continuous polymeric matrix. In the case of FRP composites the reinforcing fi bres constitute the backbone of the material and determine its strength and stiffness in the direction of the fi bres. The additives include plasticizers, fl ame retardants, blowing agents, coupling agents, etc. Other constituents in small quantities include coatings, pigments, and fi llers (GangaRao et al. 2007). To utilize the full potential of the composites in structural applications, the properties and behaviour of its constituents, the fi bres and matrices, must be understood.

��



Fibres

Fibres are used in polymeric composites because they are strong, stiff and light in weight. Fibres are stronger than the bulk material that constitutes the fi bres due to their preferential orientation of molecules along the fi bre direction and because of the reduced number of defects present in fi bres compared to the bulk material. The desirable structural and functional requirements of the fi bres in composites are high elastic modulus for an effi cient use of reinforcement, high ultimate strength and low variation of strength between individual fi bres, stability of properties during handling and fabrication, uniformity of fi bre diameter and surface, high toughness, durability, availability in suitable forms, and acceptable cost. The most common fi bres used to make FRP composites are glass, carbon and aramid. All these fi bres exhibit a linear elastic behaviour under tensile loading up to failure without showing any yielding (see Fig. 4.2). Typical properties of various types of reinforcing fi bres are summarized in Table 4.1. Diameters of the fi bres are compared in Fig. 4.3.

Glass fi bres are the most commonly used reinforcing fi bres for polymeric matrix composites. Molten glass can be drawn into continuous fi laments that are bundled into rovings. During fabrication, fi bre surfaces are coated to improve wetting by the matrix and provide better adhesion between the composite constituents. Coating the glass fi bres with a coupling agent will provide a fl exible layer at the interface, the strength of the bond is improved and the number of voids in the material is reduced. The most common glass fi bres are made of E-glass, S-glass and alkali-resistant glass. E-glass is the least expensive of all glass types and is broadly used in the fi bre reinforced plastics industry. S-glass has a higher tensile strength and higher modulus

4000

3000

2000

1000

00

ab

cd

e

1 2 3 4 5Tensile strain (%)

Tensile

str

ess (

MP

a)

4.2 Stress–strain curves of typical reinforcing fi bres: (a) carbon (high modulus); (b) carbon (high strength); (c) aramid (Kevlar 49); (d) S-glass; (e) E-glass.

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Hair

E-Glass

Aramid

Carbon

4.3 Comparison of the fi bre diameter of three most common fi bres to the human hair.

Table 4.1 Typical properties of fi bres for FRP composites

Fi bre type Density (kg/m3)

Tensile strength (MPa)

Young modulus (GPa)

Ultimate tensile strain (%)

Thermal expansion coeffi cient (10−6/°C)

Poisson’s coeffi cient

E-glass 2500 3450 72.4 2.4 5 0.22S-glass 2500 4580 85.5 3.3 2.9 0.22Alkali-resistant glass 2270 1800–3500 70–76 2.0–3.0 – –ECR 2620 3500 80.5 4.6 6 0.22Carbon (high modulus) 1950 2500–4000 350–650 0.5 −1.2 to −0.1 0.20Carbon (high strength) 1750 3500 240 1.1 −0.6 to −0.2 0.20Aramid (Kevlar 29) 1440 2760 62 4.4 −2.0 longitudinal

59 radial0.35

Aramid (Kevlar 49) 1440 3620 124 2.2 −2.0 longitudinal59 radial

0.35

Aramid (Kevlar 149) 1440 3450 175 1.4 −2.0 longitudinal59 radial

0.35

Aramid (Technora H) 1390 3000 70 4.4 −6.0 longitudinal59 radial

0.35

Aramid (SVM) 1430 3800–4200 130 3.5 – –

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than E-glass. However, the higher cost of S-glass fi bres makes them less popular than E-glass. Alkali-resistant (AR) glass fi bres, which could help prevent corrosion by alkali attacks in cement matrices, can be produced by adding zirconium.

The tensile strength of glass fi bres reduces at elevated temperatures but can be considered constant for the range of temperatures at which polymer matrices are exposed. The tensile strength also reduces with chemical cor-rosion and with time under sustained loading.

Carbon and graphite fi bres are used interchangeably, but there are some signifi cant differences between the two as far as their modular structure is concerned. Most carbon fi bres are produced by thermal decomposition of polyacrylonitrile (PAN). The carbon atoms are arranged in crystallographic parallel planes of regular hexagons to form graphite, while in carbon, the bonding between layers is weak, so that it has a two-dimensional ordering. The manufacturing process of carbon and graphite fi bres consists of oxida-tion at 200–300°C, different stages of carbonization at 1000–1500°C and 1500–2000°C and fi nally graphitization at 2500–3000°C. Graphite has a higher tensile modulus than carbon, therefore high-modulus fi bres are pro-duced by graphitization. Carbon fi bres are commercially available in long and continuous tows, which are bundles of 1000 to 160,000 parallel fi la-ments. These fi bres exhibit high specifi c strength and stiffness; in general, as the elastic modulus increases, the ultimate tensile strength and failure elongation decrease (Fig. 4.3). The tensile modulus and strength of carbon fi bres are stable as temperatures rise; they are also highly resistant to aggressive environmental factors. Carbon fi bres behave elastically up to failure and fail in a brittle manner. The greatest disadvantage of carbon fi bres is their high cost. They are 10 to 30 times more expensive than E-glass. The high cost of these fi bres is due to the high price of raw materi-als and the long process of carbonization and graphitization. Moreover, graphite fi bres cannot be easily wetted by the matrix, therefore sizing is necessary before embedding them in a matrix.

Polymeric fi bres, using a suitable processing method, can exhibit high strength and stiffness. This happens as a result of the alignment of the polymer chains along the axis of the fi bre. Aramid is a generic term for a group of organic fi bres that have the lowest specifi c gravity and the highest tensile strength-to-weight ratio among the current reinforcing fi bres. Aramid fi bres are currently produced by, for example, DuPont (Kevlar), Teijin (Technora) and Akzo Nobel (Twaron). Kevlar has very good tension fatigue resistance and low creep and it can withstand relatively high tem-peratures. The strength and modulus of Kevlar fi bres decrease linearly with rising temperatures, but they retain more than 80% of their original strength at 180°C. Kevlar fi bres absorb some water, the amount of absorbed water

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depending on the type of the fi bre, and are sensitive to UV light. At high moisture content, Kevlar fi bres tend to crack internally at the pre-existing microvoids and produce longitudinal splitting. Kevlar fi bres are resistant to many chemicals, but they can be degraded by some acids and alkalis.

Carbon and aramid fi bres are anisotropic with different values of mechan-ical and thermal properties in the main directions, whereas glass fi bres are isotropic (Eckold 1994).

Matrix

The matrix in a polymeric composite can be regarded as both a structural and a protection component. Resin is a generic term used to designate the polymer, polymer precursor material, and/or mixture or formulation thereof with various additives or chemically reactive components. In general, a polymer is referred to as a resin system during processing and a matrix after the polymer has cured. Composite material fabrication and properties are fundamentally affected by the resin, its chemical composition and physical properties. The matrix material generally accounts for between 30 and 60% by volume of a polymeric composite. The main functional and structural requirements of a matrix are to bind the reinforcing fi bres together, to transfer and distribute the load to the fi bres, and to protect the fi bres from environmental attacks and mechanical abrasion. Hence, the choice of matrix is of paramount importance when designing a composite system, and will affect both the mechanical and physical properties of the fi nal product.

There are two basic classes of polymeric matrices used in FRP compos-ites: thermosetting and thermoplastic resins. Thermosetting resins are poly-mers which are irreversibly formed from low molecular weight precursors of low viscosity. These polymers have strong bonds both in the molecules and between the molecules. They develop a network structure that sets them in shape. If they are heated after they have been cured, they do not melt and will retain their shape until they begin to thermally decompose at high temperatures.

Thermoplastics are polymers that do not develop crosslinks. They are capable of being reshaped, and repeatedly softened and hardened by sub-jecting them to temperature cycles reaching values above their forming temperature.

The term epoxy resin defi nes a class of thermosetting resins prepared by the ring-opening polymerization of compounds containing on average more than one epoxy group per molecule. Prior to adding fi bres, small amounts of reactive curing agents are added to liquid resin to initiate polymerization. Crosslinks are formed and epoxy liquid resin changes to a solid material. High-performance epoxies have been prepared with a variety of phenolics

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and aromatic amines. Epoxy resins can be partially cured; thus the rein-forcement can be pre-impregnated with liquid resin and partially cured to give a prepreg.

The main advantages of epoxy resins are good mechanical properties, easy processing, low shrinkage during curing (leading to good bond char-acteristics when used as adhesives) and good adhesion to a wide variety of fi bres. Epoxies have a high corrosion resistance and are less affected by water and heat than other polymeric matrices. Curing of such resins can be achieved at temperatures ranging between 5°C and 150°C. Epoxy resins can be formulated to have a wide range of stiffness and other mechanical properties.

The main disadvantages of epoxy resins are their relatively high cost and long curing period. The cost of epoxies is proportional to their perfor-mance, and varies over a broad range, but epoxies are generally more expensive than polyesters and vinyl esters. Furthermore, the toughness of the resin and the composite can be controlled by adding additives, including thermoplastics.

Polyester resins are low viscosity liquids based on unsaturated polyesters, which are dissolved in a reactive monomer, such as styrene. The addition of heat and a free radical initiator, such as organic peroxide, results in a crosslinking reaction, converting the low viscosity solution into a three-dimensional thermosetting matrix. Crosslinking can also be accomplished at room temperature using peroxides and suitable activators. Polyester resins can be formulated to have good UV resistance and to be used in outdoor applications. There are many glass fi bre reinforced polyester struc-tures that have been in use for more than 30 years, only affected by some discolouration and small loss in strength. Superior durability and resistance to fi bre erosion can be obtained when styrene is supplemented with methyl methacrylate (MMA). Resistance to burning of polyester resins can be achieved by using either fi ller or a specially formulated fl ame-retardant polyester resin, depending on the degree of resistance required. Incorporating halogens into a polyester resin has been found to be an effective way of improving fi re retardancy. Polyester resins are used in applications requir-ing corrosion resistance.

Some representative material data for polyester resins are given in Table 4.2. They correspond to unreinforced cast samples of resin. Using any fi brous reinforcement dramatically improves the mechanical properties of the resin. The main disadvantage of polyester resins is their high volumetric shrinkage. This volumetric shrinkage can be reduced by adding a thermo-plastic component. Crosslinking can affect the properties of polyester resins in the same manner as for epoxy resins.

Vinyl esters are resins based on methacrylate and acrylate. Some varia-tions contain urethane and ester bridging groups. Due to their chemical

��



structure these resins have fewer crosslinks and they are more fl exible and have a higher fracture toughness than polyesters. They also have very good wet-out and good adhesion when reinforced with glass fi bres. Their properties are a good combination of those of epoxy resins and polyesters and make them the preferred choice for manufacturing glass fi bre reinforced composites. They exhibit some of the benefi cial charac-teristics of epoxies such as chemical resistance and tensile strength, as well as those of polyesters such as viscosity and fast curing. However, their volumetric shrinkage is higher than that of epoxy and they have only moderate adhesive strength compared to epoxy resins. There is a great variety of vinyl ester resins available for applications up to 170°C. Vinyl ester resins are highly resistant to acids, alkalis, solvents and per-oxides. Brominated versions have high fl ame retardancy. Typical properties are given in Table 4.2.

Thermoplastic resins are softened from a solid state to be processed hot, whereupon they return to this state after processing is completed and are allowed to cool down. They do not undergo any chemical transformation during processing. Thermoplastics have high viscosity at processing tem-peratures, making them diffi cult to process. Since impregnation is impaired by high viscosity, special care must be taken to ensure contact between the fi bres and the polymeric resin (Bank 2006, GangaRao et al. 2007).

Composites with thermoplastic matrices can be repaired due to the fact that the transition to the softened state can be achieved any number of times by the application of heat. Polyether ether ketone (PEEK) is the most common thermoplastic resin for high performance applications. It has high fracture toughness, which is important for damage tolerance of composites. PEEK has very low water absorption (about 0.5% by weight) at room temperature. Polyphenylene sulfi de (PPS) is a thermoplastic with very good chemical resistance. Polysulfone (PSUL) is a thermoplastic with very high elongation to failure and excellent stability under hot and wet

Table 4.2 Typical properties of thermosetting matrices

Property Matrix

Polyester Epoxy Vinyl ester

Density (kg/m3) 1200–1400 1200–1400 1150–1350Tensile strength (MPa) 34.5–104 55–130 73–81Longitudinal modulus (GPa) 2.1–3.45 2.75–4.10 3.0–3.5Poisson’s coeffi cient 0.35–0.39 0.38–0.40 0.36–0.39Thermal expansion coeffi cient (10−6/°C) 55–100 45–65 50–75Moisture content (%) 0.15–0.60 0.08–0.15 0.14–0.30

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conditions. Some properties of these thermoplastic matrices are given in Table 4.3.

4.2.2 Theoretical and experimental determination of mechanical properties of composite laminates

For a material such as a unidirectional lamina that contains all of its fi bres aligned in one direction, the conditions of transverse anisotropy apply. The stress/strain relationship can be written as (Eckold 1994, Herakovich 1998):

εi = Sijσj 4.1

where εi and σj are components of strain and stress and the compliance matrix, Sij, is given by eqn 4.2, if the plane stress constitutive equation is assumed:

S

E E

E E

G

S S

Sij =

−

−

⎡

⎣

⎢⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥⎥

=

10

10

0 01

01

12

1

12

1 2

12

11 12

1

ν

ν22 22

66

0

0 0

S

S

⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

4.2

All components are given in the principal lamina coordinate system. Inverting eqn 4.2, the in-plane stiffness matrix is obtained:

Qij = S−1ij 4.3

The four independent constants in the stress/strain equations are E1, the modulus of elasticity in the fi bre direction, E2, the modulus in the transverse direction, ν12, Poisson’s ratio, and G12, the in-plane shear modulus. The unidirectional lamina plays an essential role in structural engineering, for

Table 4.3 Typical properties for some thermoplastic matrices

Property Matrix

PEEK PPS PSUL

Density (kg/m3) 1320 1360 1240Tensile strength (MPa) 100 82.7 70.3Tensile modulus (GPa) 3.24 3.30 2.48Tensile elongation (%) 50 5 75Poisson’s coeffi cient 0.40 0.37 0.37Thermal expansion coeffi cient (10−6/°C) 47 49 56

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example FRP bars, FRP sheets and fabrics are used in the unidirectional form as the FRP end product (Bank 2006). Furthermore, the properties of composites are often obtained experimentally using unidirectional FRP materials. The properties of a lamina can also be determined theoretically as a function of the fi bre and matrix properties and the fi bre volume content using micromechanical approaches (see Herakovich 1998). Furthermore, the unidirectional lamina is the basic building block for calculating the properties of a multilayer laminate that can be used in the structure of a FRP profi le, plate or shell.

The lamina stress–strain relation in the global coordinate system is (Herakovich 1998, GangaRao et al. 2007):

σστ

εx

y

xy

T

Q Q

Q Q

Q

T⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

= [ ]⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥[ ]−

11

11 12

12 22

66

2

0

0

0 0

xx

y

xy

Q Q Q

Q Q Q

Q Q Q

εγ

ε⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

=

⎡

⎣

⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥

11 12 16

12 22 26

16 26 66

xx

y

xy

εγ

⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

4.4

where, for plane stress problems with m = cosθ and n = sinθ

T

m n mn

n m mn

mn mn m n1

2 2

2 2

2 2

2

2[ ] = −− −

⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

4.5

T

m n mn

n m mn

mn mn m n2

2 2

2 2

2 22 2[ ] = −

− −

⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

4.6

and θ is the angle between the fi bre direction and the global x-axis.The transformed plane stress constitutive equation 4.4 can be inverted

to give:

εεγ

σx

y

xy

S S S

S S S

S S S

⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

=

⎡

⎣

⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥

11 12 16

12 22 26

16 26 66

xx

y

xy

στ

⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

4.7

where the transformed compliance, [S ], is the inverse of the transformed reduced stiffness [Q].

A multilayer laminate is composed of several laminas (or layers, or plies). Classical laminate theory (CLT) describes the linear elastic response of a thin laminated composite subjected to in-plane loads and bending moments: see, e.g., Eckold (1994) and Herakovich (1998). Individual layers are assumed to be homogeneous, orthotropic, or transversely isotropic and in a state of plane stress. The constitutive relation for a thin multilayer lami-nated composite is given as:

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N

N

N

M

M

M

A A A B B B

A A Ax

y

xy

x

y

xy

⎡

⎣

⎢⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥⎥

=

11 12 16 11 12 16

12 22 226 12 22 26

16 26 66 16 26 66

11 12 16 11 12 16

12 22 26

B B B

A A A B B B

B B B D D D

B B B D112 22 26

16 26 66 16 26 66

0

0

0

D D

B B B D D D

x

y

xy

x

⎡

⎣

⎢⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥⎥

εεγκκ yy

xyκ

⎡

⎣

⎢⎢⎢⎢⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥⎥⎥⎥⎥

4.8

where Nx, Ny and Nxy are the extensional stress resultants, and Mx, My and Mxy are the fl exural stress resultants. The [A] sub-matrix defi nes the extensional response, the [D] sub-matrix the fl exural response, and the [B] sub-matrix the extension-bending couple response. The superposition of the global stiffness matrices of all n laminas results in the sub-matrices as follows:

A Q z zk

k kk

n

[ ] = ⎡⎣ ⎤⎦ −( )−=

∑ 11

4.9

B Q z zk

k kk

n

[ ] = ⎡⎣ ⎤⎦ −( )−=

∑12

21

2

1

4.10

D Q z zk

k kk

n

[ ] = ⎡⎣ ⎤⎦ −( )−=

∑13

31

3

1

4.11

where k is the number of the lamina. The z-coordinate is defi ned according to Fig. 4.4. The thickness, hk, of each lamina is then hk = zk − zk−1.

Engineering constants for each multilayer laminate, axial and lateral E-moduli, Poisson’s ratio, and the in-plane shear modulus (Ex, Ey, νxy, Gxy) can be calculated from the inversion of eqn 4.8 (see Herakovich 1998).

On the other hand, there are several standard testing methods to deter-mine the lamina and laminate properties. The majority of tests conducted on polymer composite materials for structural engineering applications are conducted on coupons cut from as-fabricated FRP composite parts. These

Middle surface

Lamina 1

Lamina 2

xz

h/2

h/2z1

zk-1

zn-1zn zk

z2

Lamina k

Lamina n

4.4 Geometry and coordinate system of the multilayer laminate.

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tests can be conducted on unidirectional laminas, such as FRP strengthen-ing strips, sheets or FRP reinforcing bars. Similar tests can be conducted on multilayer laminates cut from an as-fabricated in-situ part. Standard test methods can be found in ASTM, ACI, CSA, JSCE, ISO, ISIS-Canada, and the European codes and guidelines. A comprehensive list of the test methods can be found in Bank (2006), Eckold (1994), GangaRao et al. (2007), ACI-440.R-07 (2007), ACI-440.1R-03 (2003), Hollaway (1993) and ISIS-Canada (2003).

4.2.3 Manufacturing techniques

Manufacturing methods for composites vary from manual to fully auto-mated processes, whereby the latter have better quality control than the former. Wet layup, pultrusion, and fi lament winding are all discussed in some detail, while other techniques such as pull-winding, resin transfer moulding, vacuum bag moulding, and injection moulding are left to special-ized composite materials texts.

Wet layup is a manual method in which the dry fabric, or mat fi bres, are fi rst laid onto the substrate or mould. Resin is then applied and rolled evenly over the surface to remove air pockets. This is repeated to obtain the required number of layers. The fabric can be pre-wetted before laying to allow for a better fi bre/matrix ratio control.

In structural rehabilitation applications, the mould is simply the existing structural member to be strengthened, and the FRP remains bonded to the mould after curing (which is normally accomplished at ambient tem-perature). This technique has the advantage that it is easily and rapidly performed in the fi eld, providing signifi cant fi nancial advantages over conventional structural rehabilitation techniques such as external plating with steel. However, quality control is extremely important in this proce-dure, and skilled labour is often required. Wet layup for structural rehabili-tation of a concrete column is illustrated in Fig. 4.5.

Pultrusion is an automated, continuous fabrication process. Design pos-sibilities are limited only by the requirement that the profi le be constant over the length of the object. Continuous fi bres in roving or mat form are drawn through a resin bath to coat each fi bre with a specially formulated resin mixture as shown in Fig. 4.6. The coated fi bres are assembled by a forming guide and then drawn through a heated die. Heating in the die and a catalyst in the resin mix initiate the curing of the thermosetting resin. Heating and cooling zones in the die control the rate of reaction. The result-ing high strength profi le is cut to length, ready for use as it leaves the pultrusion machine.

Filament winding is a process for fabricating a composite structure in which continuous fi bres (fi lament, wire, yarn, tape, or other), either previ-

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Resin injection Ventilation

Heating and curing Pulling devices Saw

Reinforcement

4.5 Column wrapping using wet layup at the Empa Switzerland Structural Engineering Laboratory.

4.6 Different devices of a pultrusion machine (FiberlineComposites 2003).

ously impregnated or impregnated during the winding with a resin matrix, are placed over a rotating and removable form or mandrel in a prescribed way to meet certain stress conditions. Generally the shape is a surface of revolution and may or may not include end closures. When the required number of layers has been applied, the wound form is cured and the mandrel removed.

4.3 Durability of composites

The durability of a material or structure has been defi ned as its ability to resist cracking, oxidation, chemical degradation, delamination, wear, and/

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or the effects of foreign object damage for a specifi ed period of time, under appropriate load conditions and specifi ed environmental conditions (Karbhari et al. 2003). Due to their different exposure situations, recent guidelines and recommendations have clearly differentiated between the factors affecting the durability of internal and external reinforcement (ACI-440.R-07 2007, ISIS-Canada 2006). For internal reinforcement, the degra-dation processes and mechanisms that affect the hygro-thermo-mechanical properties of FRP reinforcing rods include exposure to alkaline environ-ments, alternate wet and dry cycles, freezing-and-thawing conditions, tem-perature and humidity variations, and loads (creep and fatigue). External reinforcement, on the other hand, is likely to be exposed to a more varied environment than internal reinforcement, including moisture cycling, chemical solutions, and UV radiation.

This section will give descriptions of some of the most signifi cant environ-ments affecting FRP durability. This is followed by a description of the fi re performance of FRP reinforced or strengthened systems. Finally, a brief overview of the consideration of durability in guidelines, codes and stan-dards is given. The information presented in this section is based largely on information found in ACI-440.R-07 (2007) and ISIS-Canada (2006).

4.3.1 Environments affecting FRP durability

Moisture and solution effects

• General: All resins absorb moisture, with the percentage of moisture absorption depending on the resin structure, degree of cure, and tem-perature. The two primary effects of moisture uptake are plasticization and a reduction in the glass transition temperature. In general, moisture effects over the short term cause more pronounced degradation in strength as opposed to stiffness of the composite. Furthermore, salt solutions can cause blistering due to osmotic effects. In most cases, the effect of chemical solutions is on the resin system, with the absorption following a diffusion-based process similar to that of water (Karbhari et al. 2003). A large number of speciality resin systems are available that are resistant to varying levels of chemical attack and exposure.

• Internal reinforcement: A study by Sen et al. (1998) conducted over a 45-month period indicated that bond degradation adversely affected the ultimate capacity of AFRP-reinforced pretensioned piles driven in tidal waters, whereas the CFRP-reinforced piles were largely unaffected.

• External reinforcement: In adhesively bonded FRP systems, one face of the material is adhered to the concrete and one is exposed to the envi-ronment. Consequently, the exposure conditions (related to moisture) for the FRP composite are affected simultaneously by the local environ-

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ment and the underlying concrete. Highly porous concrete will readily transmit any available moisture to the bond line. Accumulation of salts at the bond line may cause large pore pressures to develop, thus reduc-ing the bond capacity. Karbhari et al. (1997) studied the effect of water, seawater, and freezing and thawing on bonded FRP systems using a peel test. They found that the nature of the bond changed and this resulted in a reduction of strength when exposed to water. Wan et al. (2003) investigated the effect of the presence of moisture on the FRP substrate during FRP application. Once again, bond behaviour deteriorated with an increase in moisture presence during the application. Chajes et al. (1995) subjected 48 small-scale beams strengthened with glass, aramid, or carbon fi bre composites to wetting and drying or freezing and thawing cycles followed by a test in fl exure. The results indicated that the beams strengthened with carbon fi bres maintained their strength better than those with glass or aramid fi bre composites.

Alkali effects

• General: The reaction of FRP composites to alkaline conditions in con-crete is a major design consideration. Alkaline solutions, such as the pore water of concrete, have a high pH and a high concentration of alkali ions. Although an appropriate resin matrix (vinylester, epoxy) provides a high level of protection to fi bres, migration of high pH solu-tions and alkali salts through the resin (at voids, cracks, and the inter-face between the fi bre and the matrix) to the fi bre surface is possible. Carbon fi bres are resistant to alkaline solutions (Meier 1995); however, resin damage via alkali attack is generally more severe than that due to moisture. E-glass fi bre systems should be properly designed and fabri-cated with the appropriate resin system to protect the reinforcement from alkali attack. Alkali-resistant glass fi bres are available and can decrease the rate of deterioration substantially.

• Internal reinforcement: Aqueous solutions with high pHs are known to degrade the tensile strength and stiffness of GFRP bars (Porter and Barnes 1998, Rostasy 1997, Sen et al. 1998, Takewaka and Khin 1996, Sheard et al. 1997, GangaRao and Vijay 1997). On the other hand, Devalapura et al. (1998) concluded that GFRP reinforcement exposed to both alkaline and acidic environments retained signifi cant load-bearing capacities for extended life cycles under conditions harsher than expected in fi eld service. Similar results were found by Mufti et al. (2005) in an ISIS-Canada-approved project to study the performance of GFRP reinforcement used in demonstration concrete structures across Canada. Based on the results of the study, Mufti et al. (2005) found no visible degradation of the GFRP reinforcement (rods and grids) in the

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concrete environment in real engineering structures exposed to natural environmental conditions for fi ve to eight years. In fact, results from scanning electron microscopy and X-ray analyses suggest no degrada-tion of the GFRP reinforcement materials and no alkali ingress in the GFRP reinforcement from the concrete pore solution. The conclusion of the project was that the GFRP reinforcement is durable and highly compatible with the concrete material.

• External reinforcement: Externally applied FRP may be in contact with soil, which can also have a high alkaline content, thereby making alkali effects also relevant for this type of reinforcement/strengthening system.

Temperature

• General: The primary effects of temperature are on the viscoelastic response of the resin, and hence of the composite. As temperature increases, the modulus of the resin will decrease. If the temperature exceeds the glass transition temperature, Tg, FRP composite perfor-mance will decrease substantially. Thermal cycling below Tg generally does not cause deleterious effects, although extended thermal cycling of brittle resin systems can result in microcrack formation (Karbhari and Eckel 1993). In general, low temperatures and freezing-and-thawing exposures do not affect fi bres, although they can affect the resin and the fi bre–resin interface. Polymeric resin systems are known to embrittle, resulting in increased strength and stiffness under sub-zero (but non-cryogenic) conditions (Chawla 1998). Freezing-and-thawing effects can be more severe due to moisture-initiated effects, causing microcrack growth and coalescence because of cycling.

• Internal reinforcement: Researchers have reported that extremely ele-vated temperatures (above the glass transition temperature) have a detrimental effect on bonds, probably because of lower shear stiffness in the FRP. The GFRP achieved the highest residual bond strength, while the AFRP achieved the lowest, but slip increased dramatically with increases in temperature in all the materials (Nanni et al. 1995, Katz et al. 1999). At low temperatures, complex residual stresses arise within FRP composites as a result of matrix stiffening and a mismatch between the coeffi cients of thermal expansion (CTE) of the matrix and the resin, as well as the FRP and concrete (Chawla 1998). Residual stresses can cause microcracks in the matrix and fi bre–matrix interface, which can grow under low-temperature thermal cycling and coalesce to form trans-verse matrix cracks and debonding between the fi bres and the matrix.

• External reinforcement: For externally bonded FRP, the bond of the FRP to the substrate can be affected by both elevated and low tempera-tures. Experience has shown that voids – regions between the concrete

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and FRP not completely fi lled with adhesive and/or resin – exist in most external FRP applications. If liquid water can get to these voids and freeze, a lensing effect is likely. The interface region will deteriorate, and the voids will grow with continued freezing-and-thawing cycles. Karbhari and Eckel (1993) tested FRP-wrapped cylinders at a low tem-perature (−18°C) and found increased brittleness of FRP fi bres at this temperature. Soudki and Green (1996) found good performance of CFRP-strengthened columns when subjected to up to 200 cycles of freezing and thawing consisting of 16 hours of freezing (−18°C) followed by eight hours of thawing in a water bath (+15°C). Chajes et al. (1995) tested FRP-strengthened concrete beams exposed to 100 freezing-and-thawing cycles and found strength losses of 21% for CFRP and 27% for GFRP.

Creep and relaxation

• General: Polymer resins generally exhibit creep and relaxation behav-iour. The addition of fi bres increases the creep resistance of the resins. Consequently, creep and relaxation behaviour are more pronounced when a load is applied transversely to fi bres or when the composite has a low fi bre volume fraction (Karbhari et al. 2003).

• Internal reinforcement: Odagiri et al. (1997) investigated relaxation char-acteristics of 6 and 7.4 mm (0.24 and 0.29 in) diameter AFRP tendons with anchorages. Overall, the relaxation rates for AFRP rods were found to be approximately 11% at 1000 hours, and 15% at 17,700 hours (two years). Creep rupture, the tensile rupture of a material subjected to sustained high stress levels over a period of time, is another important concern for FRP reinforcing bars.

• External reinforcement: Most externally bonded FRP systems are intended to strengthen an existing structure. Consequently, the level of sustained load carried by the FRP is likely to be minimal. Plevris and Triantafi llou (1994) analytically and experimentally studied the time-dependent behaviour of concrete beams strengthened with FRP plates. Three 1.5 m (4.9 ft) span beams were tested under sustained loading. From parametric studies, it was found that CFRP and GFRP laminates bonded to concrete beams improved the long-term behaviour of the strengthened beams by controlling creep strain. AFRP was not as effec-tive because of signifi cant creeping of the AFRP itself.

Fatigue

• General: FRP composites generally have very good resistance to fatigue, although the fatigue performance of FRP composite materials depends on the matrix composition and, to some extent, on the type of fi bre (Curtis

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1989). The individual fi bres within unidirectional composites have few defects, and are consequently resistant to crack initiation. Additionally, any crack that does form travels through the matrix and is not transmitted through adjacent fi bres. These toughness and crack-arresting properties contribute to good fatigue performance in FRP materials.

• Internal reinforcement: In the case of internal reinforcement, fatigue loading is more likely to affect the concrete and the bond between the concrete and the FRP reinforcement than the FRP itself. It should, however, be noted that cracking in concrete could cause abrasion-related damage to the FRP surface, which could result in higher envi-ronmental exposure to moisture and solutions.

• External reinforcement: Meier et al. (1993), Heffernan (1997), Barnes and Mays (1999), Shahawy and Beitelman (1999), Papakonstantinou et al. (2001), Masoud et al. (2001), Brena et al. (2002), Aidoo et al. (2004) and Quattlebaum et al. (2005) have all reported the fatigue testing of concrete beams with bonded FRP. In all cases, fatigue failure of the longitudinal steel reinforcement occurred, which was similar to that of the unstrengthened companion specimens. The increases in fatigue life observed in these tests were all attributed to the applied FRP reducing the stress range in the existing steel reinforcement.

Ultraviolet (UV) radiation

• General: Polymeric materials undergo degradation when exposed to UV radiation between 290 and 400 nm due to dissociation of chemical bonds (Karbhari et al. 2003). In general, effects are rarely severe in terms of mechanical performance, although some resins can show sig-nifi cant embrittlement and surface erosion. The most deleterious effect of UV exposure is generally not the UV-related damage, which is surface limited, but the potential for increased penetration of moisture and other agents via the damaged region.

• Internal reinforcement: UV radiation is not a concern for internal radiation.

• External reinforcement: Externally applied FRP composites can be pro-tected from UV-related degradation with appropriate additives in the resin, appropriate coatings, or both.

4.3.2 Consideration of durability in guidelines, codes and standards

Although the durability of FRPs is acknowledged as being of critical importance worldwide, it is addressed in a variety of different ways, often resulting in very different considerations and results. Durability is

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generally considered through the application of partial safety factors applied to material characteristics.

The American Concrete Institute guidelines (ACI-440.2R-02 2002) suggest that the design ultimate strength, ffu, be determined by modifying the reported strength, f*fu, by an environmental reduction factor, CE:

ffu = CEf*fu

f*fu = ( f fu − 3σ)

where f fu is the mean ultimate strength and σ is the standard deviation of the test population. Values of CE are specifi ed in Table 4.4, differentiated by fi bre type and general exposure conditions.

Similar considerations of durability are made in guidelines from the UK Concrete Society (TR55 2000), by fi b (fi b-bulletin-14 2001), by the Japanese code (JSCE 2001) and by the latest version of the Canadian Highway Bridge Design Code (CAN/CSA-S6-00 2000).

4.3.3 Fire resistance

At present, FRP systems are not being used to their full potential, largely because of their unknown behaviour in the event of fi re. This gap in knowl-edge is a primary factor preventing the widespread application of FRP materials in buildings.

In internal FRP reinforcing applications, where the FRPs are protected against combustion and insulated by a concrete cover, loss of bond at tem-peratures exceeding the glass transition temperature of the polymer matrix is likely to be the critical factor during fi re. In typical strengthening applica-tions involving externally bonded FRP materials, the FRPs are generally

Table 4.4 Environmental reduction factors, CE

Exposure condition Fibre and resin type Environmental reduction factor, CE

Interior exposure Carbon/epoxy 0.95Glass/epoxy 0.75Aramid/epoxy 0.85

Exterior exposure (bridges, piers and unenclosed parking garages)

Carbon/epoxy 0.85Glass/epoxy 0.65Aramid/epoxy 0.75

Aggressive environment (chemical plants and waste water treatment plants)

Carbon/epoxy 0.85Glass/epoxy 0.50Aramid/epoxy 0.70

Source: ACI-440.2R-02 (2002).

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too thin for a protective char to form, and thus the bond between the sub-strate and the FRP would probably be lost very early in a fi re. Flame spread, smoke generation and smoke toxicity are clearly serious concerns that should be addressed when unprotected, externally bonded FRP wraps are used in buildings. The following points give an overview of the most impor-tant issues related to fi re effects on FRP systems.

• Strength and stiffness at elevated temperature: As described in Section 4.3.1, FRPs exhibit reduced strength and stiffness properties at elevated temperatures. Available test data have been assembled by Blontrock et al. (1999), Bisby (2003) and Williams (2004) and show that while the carbon fi bres themselves are relatively insensitive to the effects of elevated temperatures, the strength and stiffness of the composites are signifi cantly degraded at temperatures of more than approximately 200°C.

• Bond properties at elevated temperatures: The bond, which relies heavily on the mechanical (shear) properties of the polymer matrix or adhesive, can be expected to be severely reduced at temperatures exceeding the glass transition temperature, Tg, of the matrix or the adhesive. Essentially no information is currently available on the specifi c behaviour of the bond between unprotected externally bonded FRP materials and con-crete or masonry at high temperature. For example, in the case of insulated FRP systems, it is not clear exactly how long the bond between the externally bonded FRPs and the substrate can be maintained during a fi re.

• Flame spread, smoke generation and toxicity: Sorathia et al. (1992) studied the smoke generation and toxicity characteristics of a variety of FRP formulations and demonstrated that thermoset resins com-monly used in structural FRPs generate unacceptable quantities of smoke and have relatively poor fl ame spread characteristics. The igni-tion and fl ame spread characteristics of conventional FRP systems can be signifi cantly improved by applying barrier treatments or coatings. Ceramic fabrics, ceramic or latex coatings, and intumescent coatings have been used to improve the ignition temperatures and fl ame spread characteristics of FRP systems (Sorathia et al. 1992, Apicella and Imbrogno 1999). Thicker spray-applied and board insulation systems have also been used to protect fi re-exposed FRPs, with varying degrees of success (Deuring 1994, Blontrock et al. 2000, Bisby et al. 2004, Williams 2004).

• Fire tests on FRP-reinforced or strengthened concrete: Recent fi re tests and numerical studies on FRP-reinforced beams and slabs have been performed in North America (Kodur and Baingo 1998, Saafi 2002, Kodur and Bisby 2005) and the United Kingdom (Abbasi and Hogg

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2004). Essentially, it has been shown that FRP-reinforced concrete structures behave similarly to steel-reinforced concrete structures in fi re, but that larger concrete covers are required to maintain FRP tem-peratures below acceptable limits. Initial research on externally bonded FRP-strengthened concrete members was performed in Europe by Deuring (1994), who demonstrated the extreme susceptibility of exter-nally bonded FRP fl exural strengthening systems to fi re and the need for thermal insulation of the externally bonded FRPs to maintain their effectiveness during fi re. Deuring also demonstrated that the bond between the FRP and the concrete was lost in less than 1 hour even for well-insulated systems. An extensive research programme in Canada (ISIS-Canada 2006) demonstrated that while FRP materials are sen-sitive to elevated temperatures, appropriately designed and insulated FRP-strengthened reinforced concrete beams, slabs and columns are capable of achieving fi re ratings of greater than 4 hours.

• Current treatment in codes and guidelines: Design codes and guidelines based on research from the past 15 years now exist for the application of FRP materials as internally (e.g. CAN/CSA-S6-00 2000, CAN/CSA-S806-02 2002, ACI-440.1R-03 2003) and externally bonded (e.g. ACI-440.2R-02 2002, CAN/CSA-S806-02 2002, TR55 2000) reinforcement for concrete structures. With respect to the fi re-safe design of externally bonded FRP strengthening systems for concrete, a common approach taken in existing codes and guidelines is to require that FRP materials be completely ignored during fi re. This requirement is based on the assumption that unprotected FRPs will be rendered completely ineffec-tive within minutes of fi re exposure.

4.4 Fibre reinforced polymer (FRP) composite

materials for strengthening of existing

concrete structural members (fl exural,

shear, confi nement)

In general, for externally bonded reinforcement (EBR), fabrics and strips are available. Commonly used fi bres include carbon, glass and aramid.

4.4.1 Fabrics

Fabrics have woven or non-woven fi bres in one or more directions: see Fig. 4.7. They are applied on the surface through either ‘dry’ or ‘wet’ appli-cation. ‘Dry’ application means that the impregnation resin is applied on the structure and then the fabric is applied in a dry state to the resin. By using a roller, the fabric is pressed into the resin (Fig. 4.8). Any additional

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(a) (b)

(c) (d)

4.7 Different types of fabrics: a, b, c and d (photos: Empa).

4.8 Application of fabrics on masonry (photo: Sika).

layers are applied by again applying impregnation resin and applying the dry fabric. ‘Wet’ application means that the fabric is pre-impregnated in a saturator machine and then applied in a ‘wet’ state to the surface of the structure.

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4.4.2 Prefabricated strips

Strips consist of unidirectional fi bres in the longitudinal direction of the strips that are embedded in an epoxy matrix (Fig. 4.9). They are produced in a pultrusion process. Furthermore, in addition to strips, prefabricated L-shaped strips are available (Fig. 4.10). They also have fi bres only in the longitudinal direction and are embedded in an epoxy matrix. Due to their shape, however, they cannot be produced by pultrusion and therefore require a special production process.

Strips are applied directly on the surface of a structure that is pretreated, e.g. by grinding or sand-blasting, using a two-component epoxy adhesive. Another technique is the so-called near surface mounted reinforcement (NSMR), which means that the strips are embedded into slits in the

4.9 Straight strip produced in a pultrusion process (photo: Empa).

4.10 Prefabricated CFRP L-shaped strip (photo: Empa).

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concrete. NSMR has the advantage that there is a greater bond area between the reinforcement and the concrete.

4.4.3 Prestressed systems

If strips or fabrics are applied in a prestressed state, the use of special tech-niques is necessary. Different products for anchorages using steel or FRP anchors in combinations with special prestressing devices are available on the market and/or under development: see, e.g., Kim et al. (2008).

All of these anchorage systems, however, must be fi xed to the base element with screws or dowels. A method developed at the Swiss Federal Laboratories for Materials Testing and Research (Empa) produces a decrease in the prestressing force at the strip end (see Fig. 4.11) and there-fore does not require any permanent anchorages and steel pieces (Czaderski and Motavalli 2007, Aram et al. 2008b, Motavalli et al. 2010).

In the following sections, the design of fl exural and shear strengthening as well as confi nement are described. Note that these design methods are still under development and that all equations in these sections are presented without safety factors. In an actual design, safety factors must be applied.


materials for fl exural strengthening

4.5.1 Introduction and applications

Externally bonded fl exural reinforcement (EBFR) for the strengthening of concrete members using unstressed fi bre reinforced polymer (FRP) strips

4.11 Prestressing and heating device for producing the gradient anchorage (photo: Empa).

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or fabrics is in common use worldwide. The fi bre materials used are primar-ily carbon or glass. Figures 4.12 and 4.13 show examples of applications for the fl exural strengthening of RC members.

4.5.2 Design

Debonding of the EBFR in conjunction with the internal steel reinforce-ment in an elastic or yielding state is the most common failure mode. Further failure modes of the members that can be observed are concrete

4.12 F l exural strengthening with strips of a solid slap fl oor in Warsaw due to load enlargement (photo: Prof. Kotynia).

4.13 Flexural strengthening with strips in a cement factory in Poland (photo: S&P).

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compression failure and tensile failure of FRP. Different descriptions and categorizations of debonding failure modes can be found in the literature, e.g. Aram et al. (2008a).

In general, and with some simplifi cations, three main debonding failure modes can be distinguished (Fig. 4.14):

• Debonding failure mode 1: Anchorage debonding failure at strip end• Debonding failure mode 2: Debonding at shear cracks or discontinuities

(high shear forces or discontinuities result in high shear stresses between the strip and concrete)

• Debonding failure mode 3: Debonding at fl exural cracks due to high local shear stresses.

From the variations of the equations given in the literature, e.g. fi b-bulletin-14 (2001), ISIS-Canada (2001), ACI-440.2R-02 (2002), Teng et al. (2002), CNR (2004), SIA166 (2004), TR55 (2004), it can be seen that debonding is a complex failure mode that is not yet fully understood.

To avoid debonding, the following checks for debonding failure modes using ordinary cross-section analysis are recommended.

Strip end debonding failure

The end anchorage debonding failure mode is expected for short beams, if the cracks are near to the supports and if the end of the strip is not near to the support. Furthermore, if only a small internal steel reinforcement cross-section exists, the strip must carry a larger portion of the tensile force, which also increases the danger of end anchorage failure.

A possible design strategy for avoiding strip end debonding is the limita-tion of the FRP force in the EBFR at the position of the last crack (Fig. 4.14). The existing force in the EBFR should be smaller than the force that can be anchored in a pull-off test (Fig. 4.15). The formulations for this force include typically the elastic modulus, Ef, thickness, tf, and width, bf, of the

1 23 1

4.14 Debonding failure modes of externally bonded fl exural strengthening (EBFR).

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Lengthlb

Fb

Sf0 Sf1

τf0

τf0

εf

Bond s

hear

str

ess

Bond s

hear

str

ess

Str

ain

in C

FR

P s

trip

Slip

4.15 Pull-off test and corresponding strain and shear stress on the basis of a bilinear bond shear stress–slip relation.

strip, and the tensile strength of the concrete, fct. In Czaderski et al. (2010), a theoretical derivation of the anchorage force and length can be found.

According to SIA166 (2004), the maximal force can be calculated as

F b G E t bf

E t b E t fb f Fb f f fctH

f f f f f ctH= = =2 28

0 5. 4.12

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where Fb = maximal anchorage force of a strip glued on concrete, GFb = fracture energy of a strip glued on concrete, and fctH = tensile strength of surface concrete.

The formulation in TR55 (2004) is similar, but also includes a width factor:

F k b E t f k

bbbb b f f f ctm b

f

w

f= =

−

+>0 5 1 06

2

1400

1. . 4.13

where bw = width of the strengthened beam or spacing of the strips, fctm = 0.18f cu

2/3 and fcu = characteristic compressive cube strength of concrete. Ideally, fctm should be obtained from pull-off tests on the actual concrete.

Furthermore, the existing length of the strip after the last crack must be compared with the corresponding anchorage length of the anchorage force. If the existing length is not enough, the anchorage force that can be anchored is reduced; see, e.g., SIA166 (2004) or TR55 (2004).

An alternative to the concept of limiting the force at the last crack is that shear loads at the strip end are limited (e.g. Teng et al. 2002). Furthermore, the shear and normal stresses at the strip end can be limited. The calcula-tion of these stresses using elastic solutions is given in the literature, e.g. Smith and Teng (2001).

Debonding at shear cracks or discontinuities

This debonding failure mode is expected to occur for large shear forces, for single loads and if a small distance between the load and the support exists. Furthermore, it is expected if a large internal steel reinforcement cross-section exists so that, at the point when it starts to yield, a large force transfer to the EBFR occurs and therefore a large shear stress develops. In addition, discontinuities in the internal stress state (prestressed concrete), the cross-section and the reinforcement (e.g. at joints) are potential points with high shear stresses between the strip and the concrete. Lastly, a large enough compression zone should exist, so that no premature concrete crushing occurs.

In order to prevent debonding of the strips at shear cracks or discontinui-ties, the existing shear stresses, τb, should be limited. By using ordinary cross-section analysis, the strain in the EBFR and the shear stress can be calculated using (see Fig. 4.16):

τ εb

f f f

f

= ΔΔE A

b x 4.14

where Δεf = strain change in the strip between two cross-sections, Δx = spacing between these two cross-sections, and Af = cross-section of the strip.

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For the cross-section analysis, different bond properties must be consid-ered by using the bond coeffi cients κs = 0.7 and κf = 0.9 for the internal reinforcement steel bars and the externally bonded strips, respectively. For compatibility relationships in the cross-section analysis, the mean values of the strains, εs, in the internal steel reinforcement and εf in the EBFR can be used; however, for the equilibrium relationships, the maximum values of the strains for the internal reinforcement steel bars and the externally bonded strips,

ε εκs

s

s,max = 4.15

ε εκf

f

f,max = 4.16

should be used in the cross-section analysis (SIA166 2004).Possible limits of the shear stress can be found respectively in SIA166

(2004), SIA262 (2003), Aram et al. (2008a), TR55 (2004) and fi b-bulletin-14 (2001) as:

t b c ck ckwhere characteristic value of cylind≤ = × =2 5 2 5 0 3. . .τ f f eercompression strength of concrete

4.17

τb

εf

εc, top

χ

M

4.16 Principle of determining the shear stress between the EBFR and concrete surface by using cross-section analysis.

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τb ≤ fct where fct = tensile strength of concrete 4.18

τb ≤ 0.8 N/mm2 4.19

τb ≤ 1.8 fctk where fctk = characteristic tensile strength of concrete 4.20

Debonding at fl exural cracks

Debonding at fl exural cracks is likely to occur if a lower percentage of internal steel reinforcement and therefore large forces and strains in the EBFR exists. Furthermore, small shear forces and large spans can lead to debonding at fl exural cracks. Lastly, the compression zone should be large enough so that no premature concrete crushing occurs.

In order to prevent debonding of the strips at fl exural cracks, the existing strain in the EBFR should be calculated with a cross-section analysis and limited to, e.g. respectively from SIA166 (2004), TR55 (2004) and ACI-440.2R-02 (2002):

εf,max ≤ 0.8% (≤εfu) 4.21

εf ≤ 0.8% (≤εfu) 4.22

εf ≤ κmεfu 4.23

where

κεm

fu

f ff ffor= −⎛

⎝⎜⎞⎠⎟ ≤ =1

601

360 0000 90 180 000

nE tnE t

,. , 4.24

κεm

fu f ff ffor= ⎛

⎝⎜⎞⎠⎟ ≤ >1

6090 000

0 90 180 000,

. ,nE t

nE t 4.25

where n = number of plies and εfu = ultimate strain of the FRP (ACI-440.2R-02 (2002) specifi es this limit not only for debonding failure mode 3, but for debonding in general).

4.5.3 Verifi cation of serviceability limit state (SLS) of EBFR

The fundamental idea behind the SLS verifi cation is to limit the strain in the EBFR to ensure that the internal steel reinforcement does not yield at serviceability. The strains in the internal reinforcement, εs, and in the EBFR, εf, can be calculated using cross-section analysis identical to that used for the ultimate limit state and should be limited to

ε εs fy

s

= ≤ 0 8.f

E 4.26

where fy = yield stress and Es = elastic modulus of the internal reinforcement.

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Aside from the verifi cation of the strains (stresses), the determination of the defl ection and crack width might be of interest. The defl ections can be determined through a double integration of the curvature, which can also be determined using the cross-section analysis (Fig. 4.16). For calculation of the crack width, see fi b-bulletin-14 (2001).

4.5.4 Ductility

To ensure enough ductility of the strengthened structure at failure, fi b-bulletin-14 (2001) gives limitations for the minimum strain in the internal reinforcement:

εs ≥ 0.0043 for concrete types C35/45 or lower 4.27

εs ≥ 0.0065 for concrete types higher than C35/45 4.28

4.5.5 Verifi cation of accidental situation of EBFR

To prevent sudden failure of the whole structure after failure of the EBFR due to impact, vandalism, fi re, etc., a safety factor greater than 1 should remain for the unstrengthened structure.


materials for shear strengthening

4.6.1 Introduction and a pplications

Figures 4.17 and 4.18 show examples of applications of FRP for shear strengthening. Figure 4.19 shows schematically a selection of some

4.17 Shear and fl exural strengthening due to new holes in a beam in a building in Switzerland (photo: Empa).

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4.18 Shear and fl exural strengthening with strips and fabrics in a cement factory in Poland (photo: S&P).

4.19 Some possible shear strengthening principles using FRP.

possibilities of how FRP can be used for shear strengthening of reinforced concrete. The main problem is to fi nd solutions for the anchorage of the FRP in the fl ange for the case of T-beams. There are several solutions to this problem, e.g. by drilling holes or slits and gluing in the FRP or using dowels. A further important point is that the corners must be prepared properly to ensure a good force transfer of the shear strengthening.

For shear strengthening, fabrics that are applied on the entire side of the webs, Fig. 4.18, or in the form of sheets with certain spacings, can be used. Prefabricated CFRP L-shaped strips, Figs 4.10 and 4.17, are also an alternative.

4.6.2 Design

Usually, for shear design the well-known classical truss model is used. The shear strengthening design also requires knowledge and understanding of the crucial failure modes of the externally bonded shear reinforcement (EBSR).

Similar to the design of fl exural strengthening, the following states for the shear design of reinforced concrete (RC) members can be distinguished as the structural loads increase:

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State I: Uncracked cross-section, i.e. no shear cracks exist, the concrete carries the whole load, virtually no stress in the shear reinforcement.

State II: Shear cracks exist, the internal shear reinforcement (ISR) is in the elastic region, the ISR and the EBSR carry the load in proportion to their stiffness.

State III: Shear cracks exist, the ISR yields and the EBSR carries the further increase in load.

Figure 4.20 shows the principle of the three states. In the fi gure, the numbers 1 and 2 indicate the start of the yielding of internal shear reinforcement and the failure of externally bonded shear reinforcement, respectively.

The shear resistance of a RC member can be defi ned as the minimum of the sum of three contributions, or the failure of the compressive struts:

VR = min(VR,c + VR,s + VR,f, VR2) 4.29

where VR = shear resistance of RC member, VR,c = concrete contribution (fi rst shear crack, state I), VR,s = contribution of internal steel stirrups (ISR), VR,f = contribution of externally bonded shear reinforcement (EBSR), and VR2 = failure of compressive struts.

According to the codes, the strut inclination can be freely chosen within certain limits; see, e.g., SIA262 (2003). As FRP is a purely elastic material,

VR,c

V

ε1 2

State I

State II

State III

Only ISR

Only EBSR

ISR plus EBSR

4.20 Load–strain diagram for shear reinforcement.

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no force redistribution between the EBSR is possible. Consequently, it is recommended that the strut inclination is limited to α ≥ 45°. The chosen value of α must be the same for the contribution of the ISR and the EBSR.

Several equations for the concrete contribution can be found in the rel-evant literature. However, this equation describes the design shear resis-tance of a RC member without shear reinforcement. It is important to note that this defi nition for the concrete contribution is different from the defi ni-tion of ‘State I’ given above in this section. To determine VR,c, the load at the fi rst shear crack should be calculated. Additionally, all the usual design verifi cations for RC (failure of the concrete struts, shift of moment line, etc.) have to be considered. For ductility reasons, the member should have a minimum internal shear reinforcement ratio, otherwise strengthening is not recommended.

4.6.3 Verifi cation of ultimate limit state (ULS) of EBSR

The ULS shear resistance of a member can be calculated using eqn 4.29. It is recommended that the concrete contribution (VR,c = 0) is neglected. The contribution of the internal steel stirrups, VR,s, can be calculated using the truss model (assuming a shear reinforcement inclination of 90°) such that:

V A Ezs

f

ER s s s s

s

ss

y

s

if State II, cot= < ( )ε α ε 4.30

V A fzs

f

ER s s y

s

ss

y

s

if State III, cot= ≥ ( )α ε 4.31

where εs = strain in the steel stirrups, As = cross-section of ISR, zs = internal lever arm (see Fig. 4.21), ss = spacing of ISR, α = strut inclination, and fy = yield strength of ISR.

The contribution of the EBSR, VR,f, can also be calculated using the truss model (assuming a shear reinforcement inclination of 90°) such that:

V A Ezs

R f f f ff

f

States II and III, cot= ( )ε α 4.32

where εf = strain in EBSR according to eqns 4.33 and 4.34, Af = cross-section of EBSR, zf = internal lever arm (see Fig. 4.21) and sf = spacing of EBSR.

According to Triantafi llou and Antonopoulos (2000) and fi b-bulletin-14 (2001), εf may be used for calculation of the EBSR contribution as follows (note that in eqns 4.33 and 4.34 fcm is in MPa and Efu is in GPa):

For fully wrapped (or properly anchored) CFRP, FRP fracture controlled:

ερ

εfcm

fu ffu= ⎛

⎝⎜⎞⎠⎟

0 172 3 0 3

..

fE

4.33

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zsd zf

45°

4.21 The geometry of a T-cross-section.

where fcm = mean value of the concrete compressive strength; Efu = elastic modulus of the EBSR; ρf = EBSR reinforcement ratio, which is equal to 2tf/bw for continuously EBSR and 2tf/bw(bf/sf) for EBSR in the form of strips or sheets, where tf, bf and sf = thickness, width and spacing, respectively, of the EBSR, and bw = width of concrete cross-section; and εfu = ultimate tensile strain of FRP.

For side or U-shaped CFRP jackets:

εfcm

fu f

cm

fu f

= ⎛⎝⎜

⎞⎠⎟

× ⎛⎝⎜

⎞⎠⎟

−min . , .. .

0 65 10 0 172 3 0 56

32 3 0

fE

fEr r

330

εfu

peeling-off FRP fracture

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥ 4.34

The fracture controlled strain is smaller than the ultimate tensile strain of the FRP, because of stress concentrations at, for example, rounded corners (Triantafi llou 1998).

If the EBSRs are not closed to the top, the internal lever arm, zf, is theo-retically smaller than zs (see Fig. 4.21). It is recommended that zf be calcu-lated using the centroid of the force propagation zone, which is shown schematically in Fig. 4.21 for a T-shaped cross-section; see SIA166 (2004). This principle of using the centroid of the force propagation can also be adapted for shear strengthening of rectangular cross-sections or shear strengthening without anchorage in the fl ange.

The following failure modes must be considered when verifying the con-tribution of CFRP L-shaped strips for the shear resistance of a member (see Fig. 4.10).

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Failure mode: opening of the overlapping of CFRP L-shaped strips

For CFRP L-shaped strips (Sika® CarboShear L®) with a width of 40 mm, it is recommended that the ultimate limit state of the contribution of the external CFRP L-shaped strips be calculated using a maximum force in one CFRP L-shaped strip of Ff = 45 kN if applied with overlapping (Czaderski 2002). This value is derived from the ‘opening of the overlap-ping’ failure mode, which was observed during testing of a beam. The web width should be not less than 150 mm, and the overlapping length not less than 100 mm.

Failure mode: anchorage pull-out of CFRP L-shaped strips

This failure mode can be prevented by following several recommendations. The anchor length must be chosen as long as possible, if possible the whole height of the fl ange. The internal lever arm, zf, for the fl exural and shear design should be calculated according to the principle shown in Fig. 4.21. The anchorage hole must be carefully fi lled with adhesive to ensure no air is entrapped. The anchor length should exceed 100 mm. With this minimum anchor length, the ‘anchorage pull-out’ failure mode should not be crucial.

Failure modes: ‘peeling-off’ and CFRP plate fracture

Where a rectangular cross-section must be strengthened with CFRP L-shaped strips, anchorage in the fl ange, as with a T-section, is not possible. In such cases, the ‘peeling-off’ failure mode is expected. Here, the use of eqn 4.34 is recommended to determine the design value for maximum strain in the CFRP plates. Equations 4.33 and 4.34 give the FRP fracture strain.

4.6.4 Verifi cation of serviceability limit state (SLS) of EBSR

Similar to EBFR, the SLS verifi cation is to limit the strains in the EBSR strip to ensure that the internal steel stirrups do not yield at SLS (State III is not allowed):

ε εs fy

s

State I or II= ≤ ( )0 8.f

E 4.35

The SLS shear resistance can be calculated using eqns 4.29, 4.30 and 4.32, while the strains are determined using eqn 4.35. Contrary to the verifi cation of ULS where the concrete contribution VR,c should be neglected, for the verifi cation of the SLS the concrete contribution can be included in the calculation.

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4.6.5 Verifi cation of accidental situation of EBSR

Similar to EBFR, to prevent sudden failure of the whole structure after failure of the EBSR due to impact, vandalism, fi re, etc., a safety factor greater than 1 should remain for the unstrengthened structure.

4.6.6 Fatigue of EBSR

The maximum (εf,fat,max) and differential (Δεf,fat) tensile strains in the EBSR resulting from fatigue loads have to be limited. A proposal for CFRP L-shaped strips based on fatigue test results (Czaderski and Motavalli 2004) is given in eqns 4.36 and 4.37. In the test the CFRP L-shaped strips exhib-ited no damage at 5 million load cycles. The following values do not include safety factors:

εf,fat,max ≤ 0.2% (tensile strain corresponding to upper load) 4.36

Δεf,fat ≤ 0.04% (tensile strain amplitude) 4.37


materials for confi nement

4.7.1 Introduction and applications

The aim of confi nement is to increase the axial loading capacity and/or to increase the compression strain of the concrete (see Fig. 4.22), which

4.22 Application of CFRP fabrics for confi nement of concrete columns in a football stadium in Italy (photo: Sika).

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consequently increases the ductility (deformation capacity) of the cross-section. Further benefi ts that result from confi nement are delayed buckling of the internal vertical steel rebars and an improvement in the behaviour of the lap splices. Naturally, the shear strength of the confi ned columns also increases. Figures 4.22 and 4.23 show examples of the application of confi nement to concrete columns.

4.7.2 Design

The main difference in the design of FRP compared to conventional inter-nal stirrups and external jackets made of steel is the absence of a yield plateau in the case of FRPs, and therefore not a constant confi nement pres-sure on the strengthened member.

4.23 Prestressed confi nement using aramid strips (photo: S&P).

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4.7.3 Increasing the ultimate compression strain of concrete

On the basis of other references, Mander et al. (1988) presented a calcula-tion of the stress–strain behaviour of concrete. The ultimate compression strain of confi ned concrete can be calculated as:

ε εcc cocc

co

= + −⎛⎝⎜

⎞⎠⎟

⎛⎝⎜

⎞⎠⎟

1 5 1ff

4.38

where fcc = peak strength of confi ned concrete, εcc = peak strain of concrete, fco = strength of unconfi ned concrete and εco = ultimate strain of unconfi ned concrete. Figure 4.24 shows the typical effect of confi nement on the stress–strain diagram.

4.7.4 Increasing the axial strength

For a constant confi ning pressure, the increased strength can be calculated using the equation from Mander et al. (1988):

ff

ff

ff

cc

co

l

co

l

co

= + − −2 254 1 7 94 2 1 254. . . 4.39

εco

fco

fcc

fcu

εcc εcu ε

σ

Unconfined

Steel confinement

FRP confin

ement

4.24 Typical effect of confi nement on stress–strain diagram.

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where fl = constant confi ning pressure.The confi ning pressure, σl, can be calculated as (see Fig. 4.25)

σρ σ

lj j=2

4.40

where ρj = transverse ratio of the confi nement = 4tj/dj for fully wrapped confi nement jackets, tj = thickness of confi nement jacket, dj = diameter of confi nement jacket and σj = stress in the confi nement jacket (fi b-bulletin-14 2001).

The maximum confi ning pressure fl is:

fE

lj j ju=

ρ ε2

4.41

where Ej = elastic modulus of the confi nement jacket and εju = maximum strain in the confi nement jacket. Experiments showed that εju < εfu = ulti-mate strain of the jacket. Possible reasons are the triaxial state of stress in the confi nement jacket, the quality of execution, the curved shape of the confi nement jacket (corners with small radii) and the size effect when applying multiple layers (fi b-bulletin-14 2001).

Different approaches for defi nition of the maximum strain in the confi ne-ment jacket can be found in the literature, e.g. in SIA166 (2004) where:

εju = 0.002 4.42

or in ACI-440.2R-02 (2002) for members which are subjected to combined compression and shear where:

εju = 0.004 ≤ 0.75εfu 4.43

tj

dj

σjσj

σ1

4.25 Confi ning pressure due to confi nement jacket.

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‘Exact’ as well as approximate expressions for the calculation of the ulti-mate compressive strength, fcu, and strain, εcu, of FRP confi ned concrete behaviour can be found in Spoelstra and Monti (1999). The approximate expressions are given below:

f fff

cu col

co

= +⎛⎝⎜

⎞⎠⎟

0 2 3. 4.44

ε ε εcu coc

coju

l

co

= +⎛⎝⎜

⎞⎠⎟

2 1 25.Ef

ff

4.45

where Ec = initial tangent modulus of elasticity of concrete.

4.7.5 Confi nement effectiveness

It must be noted that the confi nement effectiveness can signifi cantly decrease in any of the following cases:

• Partial wrapping of confi nement jacket• Fibre orientation not perpendicular to column axis• A non-circular column shape.

To consider these effects, confi nement effectiveness coeffi cients can be found in the literature (fi b-bulletin-14 2001).

4.7.6 Prestressed confi nement

If a confi ned concrete column is subjected to a high load, e.g. during an earthquake, the residual strength of the concrete core of the column can decrease signifi cantly. This can be a safety problem if the confi nement fails, e.g. due to a fi re. The prestressing of the confi nement reinforcement has a considerable benefi cial effect on the residual strength of the concrete (Janke et al. 2009). Due to the fact that prestressing of the usual confi ne-ment reinforcement such as steel and FRP is diffi cult, new materials such as shape memory alloys (Janke et al. 2005, Dong et al. 2009, Motavalli et al. 2010) might be available in the future for the use of prestressed confi nement.


materials for strengthening of existing

masonry structures

Practical applications in recent years have shown that FRPs can be used as an alternative strengthening material for masonry structures, especially

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those of considerable historical importance. Some of the fi rst research worldwide was conducted at the Swiss Federal Laboratories for Materials Science and Technology (Empa) (Schwegler 1994). FRP strips and fabrics were applied to the masonry shear walls in the laboratory using epoxy adhesives. The walls were then tested under static cyclic loading. It was shown that the in-plane deformation capacity of the masonry shear walls after strengthening could be increased up to 300% if the ends of the FRP strips were anchored properly.

A number of historic buildings, especially in Italy, Greece and Portugal, were retrofi tted by applying FRP composites. Aramid and glass FRP were applied for restoring the Basilica of St Francis of Assisi in Italy. This his-toric building was severely damaged by earthquakes and aftershocks in September and early October 1997 (Motavalli and Czaderski 2007).

Figures 4.26 and 4.27 show the retrofi tting of one of the masonry towers of the ancient Vercelli castle in Italy by applying CFRP rods bonded into the space between the bricks. One of the four towers showed wide vertical cracks. Reinforcement of the outer side of the masonry wall was necessary. This was achieved by wrapping horizontal CFRP rods around the tower to prevent further opening of the cracks. The rods were bonded using epoxy resin. The strengthening was completed in May 2004.

Figure 4.28 shows the seismic upgrading of the masonry shear walls of a school building in Bern, Switzerland. GFRP fabrics were glued to the surface of the walls followed by CFRP strips, which were applied crosswise on the GFRP fabric layer. The strip ends were anchored in the RC decks

4.26 Carbon rods bonded into the space between the bricks as reinforcement, Vercelli Castle, Italy (from Motavalli and Czaderski 2007).

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4.27 View into the castle and of the tower under strengthening and repair works, Vercelli Castle, Italy (from Motavalli and Czaderski 2007).

4.28 Seismic retrofi tting of a masonry shear wall using GFRP fabric and additional CFRP strips, which are anchored in concrete using end plates; school building at Zollikofen in Bern, Switzerland (from Motavalli and Czaderski 2007).

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using steel plates. Nowadays, due to the great variability of masonry properties, few guidelines, still in progress, are available for the design of FRP strengthening systems applied on masonry structures (ACI 440.7R-10 2010, CNR 2004).

Figure 4.29 shows the seismic retrofi tting of a masonry wall of the Shariati Museum in Tehran, Iran, where CFRP strips were applied.

RILEM has recently established a new technical committee (TC) entitled ‘Masonry Strengthening with Composite Materials’. The preliminary work of the TC will be the systematization of the current knowledge on the struc-tural behaviour of masonry constructions and components streng thened with composite materials, with the fi nal aim of a possible proposal of inter-national recommendations including design tools, quantitative and qualita-tive evaluation measures, limitation parameters of effi ciency and simple experimental procedures (RILEM Technical Committee (TC), Masonry Strengthening with Composite Materials (MSC), www.rilem.net, International Union of Laboratories and Experts in Construction Materials, Systems and Structures). It might also be worth mentioning that ACI will soon be publish-ing a code 440.ZR: Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Unreinforced Masonry Structures.


materials for internal reinforcement

Many types and shapes of FRP materials are now available in the construc-tion industry. For the purposes of tensile reinforcement of concrete, the currently available reinforcing products include unidirectional FRP bars,

4.29 Seismic retrofi tting of a masonry shear wall using CFRP strips; Shariati Museum in Tehran, Iran (from Radyab Co., Tehran, Iran).

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which have fi bres oriented along the axis of the reinforcement only, and orthogonal grids, which have unidirectional bars running in two (or some-times three) orthogonal directions.

Unidirectional FRP materials used in concrete reinforcing applications are linear elastic up to failure, and they do not exhibit the yielding behav-iour that is typically displayed by conventional reinforcing steel. The dif-ferences in behaviour between FRPs and steel have signifi cant consequences for the design of FRP-reinforced concrete members, since yielding of rein-forcement in steel-reinforced concrete members is used implicitly to provide ample warning of impending failure.

The excellent durability of FRP reinforcing materials in concrete, which has the potential to increase the service lives of structures while reducing inspection and maintenance costs, makes them cost-effective when the entire life-cycle cost of a structure is considered, rather than the initial construction cost alone.

Another frequently cited potential disadvantage of FRP materials is their relatively low elastic modulus as compared with steel. This means that FRP-reinforced concrete members are often controlled by serviceability (defl ec-tion) considerations, rather than strength requirements.

The properties of the bond between FRP reinforcing bars and concrete depend on the surface treatment applied to the FRP reinforcing bar during manufacturing, the mechanical properties of the FRP, and the environmen-tal conditions to which the bar is subjected during its lifetime. Again, gen-eralizations are diffi cult to make, although the bond between currently available FRP reinforcing materials and concrete appears equivalent (or superior in some cases) to that between steel reinforcement and concrete. The bond of FRP bars to concrete does not depend on the concrete strength, as it does for steel reinforcement.

A description of the durability of internal FRP reinforcement can be found in Section 4.3.

4.9.1 Design

The design procedure for FRP-reinforced concrete can be found in ACI-440.1R-03 (2003), ACI-440.R-07 (2007), fi b-bulletin-40 (2007) and ISIS-Canada (2003). Design recommendations are based on limit states design principles in that an FRP-reinforced concrete member is designed based on its required strength and then checked based on its required stiffness and fatigue endurance, creep rupture endurance, and serviceability criteria. In many instances, serviceability criteria or fatigue and creep rupture endurance limits may control the design of concrete members reinforced for fl exure with FRP bars (especially aramid and glass FRP, which exhibit low stiffness).

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The design of FRP-reinforced concrete members in fl exure is analogous to the design of steel-reinforced concrete members. Flexural capacity can be calculated based on assumptions similar to those made for members reinforced with steel bars. The design of members reinforced with FRP bars should take into account the mechanical behaviour of the FRP materials (ACI-440.1R-03 2003).

There are three potential fl exural failure modes for FRP-reinforced con-crete sections (ISIS-Canada 2003):

• Balanced failure – simultaneous FRP tensile rupture and concrete crushing

• Compression failure – concrete crushing prior to FRP tensile rupture• Tension failure – tensile rupture of the FRP prior to concrete

crushing.

Compression failure is the most desirable of the above failure modes. This failure mode is less abrupt than tension failure, and is similar to the failure of an over-reinforced section when using steel reinforcement. Tension failure is less desirable, since tensile rupture of FRP reinforcement will occur with less warning. Tension failure will occur when the reinforcement ratio is below the balanced reinforcement ratio for the section. This failure mode is permissible with certain safeguards.

Serviceability considerations, relating both to cracking and to defl ection, are crucial factors in the design of FRP-reinforced concrete fl exural members. FRP reinforcing bars generally have much higher strengths than the yield strength of conventional steel reinforcement. However, the modulus of elasticity of FRP materials is generally less than that of reinforc-ing steel, and this can lead to the formation of large cracks or to unservice-able defl ections. The result is that, in many cases, serviceability considerations may control the design of FRP-reinforced concrete members. For example, the ISIS design guidelines suggest that cracking should be controlled such that the maximum strain in tensile FRP reinforcement at service should not exceed 0.2%.

4.9.2 Applications

Information on a variety of additional fi eld applications can be obtained from the ISIS-Canada website (www.isiscanada.com). Figure 4.30 shows the placement of GFRP and CFRP reinforcement in the Wotton Bridge deck. The Wotton Bridge (Fig. 4.31), in the municipality of Wotton, Québec, is a single-span prestressed concrete girder bridge with a total length of 30.6 metres and a width of 8.9 metres. The deck slab rests on four prestressed concrete girders, spaced at 2.3 metres, with a cantilever slab of 1 metre on

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4.30 Placement of GFRP and CFRP reinforcement in the Wotton Bridge deck (from ISIS-Canada 2003).

4.31 The completed Wotton Bridge (from ISIS-Canada 2003).

either side. The deck slab is reinforced internally with ISOROD GFRP and CFRP reinforcing bars with diameters of 15 mm and 10 mm respectively. FRP reinforcement is used for both top and bottom slab reinforcement. The construction of the bridge was completed in October 2001 and it was opened for traffi c in the fi rst week of November 2001. The bridge is well instrumented at critical locations for internal temperature and strain data collection using 44 fi bre optic sensors. These gauges are used to monitor the deck behaviour from the time of construction to several years after completion of construction. Under real service conditions, strains in FRP bars due to temperature changes were 25 to 33 times those due to truck-loads. However, these maximum strains are in the order of 500 micro-strains, which represent approximately 3–4% of the ultimate strain of the material.

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materials for profi les

A brief overview of the use of FRP profi les in the design of engineering structures is given. The section focuses on commercially manufactured pultruded FRP profi les (Fig. 4.32).

Pultruded profi les consist of fi bre reinforcement (typically glass fi bre or carbon fi bre) and resins (typically polyester, vinylester or epoxy polymers). The volume fraction of the fi bre reinforcement is between 30% and 50%. The profi les consist of longitudinal continuous fi bre bundles and continuous fi bre mats in the vicinity of the surfaces of the cross-section. Due to the production methodology, only constant cross-section profi les can be pro-duced. Due to the production process, there is no limit to the length of the profi les. Restrictions are given by transportation. There are no standard geometries or standard mechanical properties of the profi les from the dif-ferent manufacturers. There are, however, standard cross-section shapes which are available from stock by most manufacturers (e.g. Fiberline, Denmark; TopGlas, Italy; Strongwell and Creative Pultrusion, USA). Beside these conventional profi les, special cross-sections can be manufac-tured, whereby special cross-section tools must be designed. In order to economically apply these special profi les, several kilometres of material must be ordered. In general, the costs of pultruded profi les made of glass fi bres is between E4 and E10 per kilogram due to the highly industrialized manufacturing technique, thereby making them an economically competi-tive material.

There are several situations in which structures made out of pultruded FPR profi les are competitive:

Angle U-profile I-profile Plank

Tubes Flat profile Square tubes T-profile

4.32 Conventional pultruded cross-sections.

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• Signifi cant corrosion and chemical resistance is required (food and chemical processing plants, cooling towers, offshore platforms, etc.)

• Electromagnetic transparency or electrical insulation is required (shield-ing of antennas, etc.)

• Light weight leads to signifi cant cost savings, fast deployment (Fig. 4.33), and removable structures like the Pontresina bridge (Fig. 4.34)

• Prestige and demonstration objects (GFRP Eyecatcher building in Basel, etc.).

Design basics for the use of FRP profi les in civil engineering applications are provided in ASCE (1984) and EUROCOMP (1996), but these two documents do not have model code-like status. Additionally, there exist design manuals published by the manufacturers of pultruded FRP profi les, e.g. FiberlineComposites (2003). Beside the design concept, all the neces-sary material parameters and associated material safety factors are given in these manuals.

There exist several design philosophies: the allowable stress design (ASD), the load and resistance factor design (LRFD) and the limit state design (LSD). The fundamental basis of LSD, commonly used in Europe, is that the level of safety or serviceability provided by a design must produce a quantifi able level of structural reliability. Nominal loads are multiplied by probabilistically derived load factors, which depend on the load type and the load combinations. The design values of the effect of the actions (Ed) are calculated. On the other hand, material partial safety factors are defi ned, accounting for the methods in which the material properties were obtained, the manufacturing process and the effects of the environment and the duration of loading. The design resistance, Rd (ultimate limit state), and the

4.33 Specially designed GFRP profi le for use in noise barrier construction beside railway tracks (photo: MaagTechnic, Switzerland).

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design limiting condition, Cd (serviceability limit state), are calculated. It must be shown that Ed ≤ Rd and Ed ≤ Cd.

Quite often the design of structures made of FRP profi les is driven by serviceability criteria such as maximum defl ections. Therefore, it is recom-mended that the design iteration procedure be started using serviceability criteria.

Since pultruded profi les have low shear stiffness, shear deformations must be taken into account. Additionally, second-order effects like lateral–torsional buckling have to be considered carefully.

The connections of pultruded FRP profi les are divided into three cat-egories: mechanical joints (bolted connections), bonded joints and com-bined joints (see Fig. 4.35). Since the strengths of the profi les in the different directions are essential in the design, guidelines for mechanical joints are found in the design manuals of the different manufacturers of FRP profi les. Only a few design rules exist for the special confi guration of bonded and combined joints. The behaviour of such joints is often investigated using the fi nite element method in combination with experi-mental data.

4.34 Pontresina bridge in Switzerland (project and picture: http://www.kuenzle.hbt.arch.ethz.ch).

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4.11 Future developments

4.11.1 New material developments

The price of carbon fi bre is not likely to drop further than it has done in the last 30 years. Increasing energy costs of processing may even increase the price of the fi bres. Modern production techniques for CFRP strips made from thermoplastic polymers rather than thermosetting matrix systems may likewise help to stabilize the likely increasing cost of carbon fi bres (Meier 2007). According to Meier (2007), thermoplastic matrices will replace epoxy matrices within the coming decade. Furthermore, more research is needed to investigate FRP properties and their bond behaviour at elevated tem-peratures. The fi re resistance of FRP composites must be improved. Heat-resistant composites for very high temperatures need to be developed. The application of prepregs instead of strips as strengthening material should be investigated, because prepregs do not require an additional adhesive in order to apply them to the structure, and therefore their application might be easier and faster.

Nanotubes in polymer composites would serve to increase the stiffness, strength and toughness, and provide other properties such as electrical and thermal conductivity. Since, at present, nanotubes can be manufactured only at lengths up to the submillimetre scale (thereby falling into the short-fi bre category), their dominant role in composites is likely to remain as matrix modifi ers and providers of multifunctional attributes in the foresee-able future. However, once nanotubes can be effi ciently assembled on a

4.35 Mechanical connections of the FRP laboratory bridge at Empa, Switzerland.

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macroscopic scale, they could become serious competition for the continu-ous carbon fi bres that are woven and stacked to form load-bearing elements in structural composites used in the building and engineering industries (Ajayan and Tour 2007).

Nanotubes can have diameters ranging from 1 to 100 nm and lengths of up to millimetres. Their densities can be as low as 1.3 g cm−3 and their Young’s moduli are superior to those of all carbon fi bres, with values greater than 1,000,000 MPa. The highest measured strength for a carbon nanotube is 63,000 MPa, which is an order of magnitude stronger than high-strength carbon fi bres (Coleman et al. 2006). However, a large amount of work will have to be done before we can really make the most of the excep-tional mechanical properties of carbon nanotubes.

4.11.2 Prestressing technology

Today in construction, only approximately 15% of the potential strength of CFRP strips is used. One important reason for this poor effi ciency is that many strengthening tasks are controlled by stiffness, not strength. The focus of future developments should therefore be on better exploitation of the potential offered by CFRP composites and on a change to thermoplastic

4.36 Automated device for simultaneous application of fi ve pre-tensioned CFRP strips (Meier 2007).

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matrix systems in order to reduce cost. Better exploitation is possible when the CFRP strips are pre-tensioned (Meier 2007). Highly automated fl exible track systems will revolutionize rehabilitation work in the construction industry (Fig. 4.36).

4.12 References

Abbasi, A. and P. J. Hogg (2004). Fire testing of concrete beams with fi bre rein-forced plastic rebar. In Advanced Polymer Composites for Structural Applications in Construction, ed. L. C. Hollaway, Cambridge, UK, Woodhead Publishing, pp. 445–456.

ACI-440.2R-02 (2002). Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures. Farmington Hills, MI, American Concrete Institute.

ACI-440.1R-03 (2003). Guide for the Design and Construction of Concrete Reinforced with FRP Bars. Farmington Hills, MI, American Concrete Institute.

ACI-440.R-07 (2007). Report on Fiber-Reinforced Polymer (FRP) Reinforcement for Concrete Structures. Farmington Hills, MI, American Concrete Institute.

ACI 440.7R-10 (2010). Guide for the Design and Construction of Externally Bonded Fibre-Reinforced Polymer Systems for Strengthening Unreinforced Masonry Structures.

Aidoo, J., K. A. Harries and M. F. Petrou (2004). Fatigue behaviour of CFRP-strengthened reinforced concrete bridge girders. Journal of Composites for Construction 8(6): pp. 501–509.

Ajayan, P. M. and J. M. Tour (2007). Nanotube composites. Nature 447(June): pp. 1066–1068.

Apicella, F. and M. Imbrogno (1999). Fire performance of CFRP-composites used for repairing and strengthening concrete. Fifth ASCE Materials Engineering Conference, New York, pp. 260–266.

Aram, M. R., C. Czaderski and M. Motavalli (2008a). Debonding failure modes of fl exural FRP-strengthened RC beams. Composites Part B: Engineering 39(5): pp. 826–841.

Aram, M. R., C. Czaderski and M. Motavalli (2008b). Effects of gradually anchored prestressed CFRP strips bonded on prestressed concrete beams. Journal of Composites for Construction 12(1): pp. 25–34.

ASCE (1984). Structural Plastics Design Manual. New York, American Society of Civil Engineers.

Bakis, C. E., L. C. Bank, V. L. Brown, E. Cosenza, J. F. Davalos, J. J. Lesko, A. Machida, S. H. Rizkalla and T. C. Triantafi llou (2002). Fiber-reinforced polymer composites for construction – State-of-the-art review. Journal of Composites for Construction 6: pp. 73–87.

Bank, L. C. (2006). Composites for Construction: Structural Design with FRP Materials. Hoboken, NJ, John Wiley & Sons.

Barnes, A. R. and C. G. Mays (1999). Fatigue performance of concrete beams strengthened with CFRP plates. Journal of Composites for Construction 3(2): pp. 63–72.

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Bisby, L. A. (2003). Fire Behaviour of FRP Reinforced or Confi ned Concrete. PhD thesis, Department of Civil Engineering, Queen’s University, Kingston, Ontario, Canada, p. 371.

Bisby, L. A., M. F. Green and V. K. Kodur (2004). Performance in fi re of FRP-confi ned reinforced concrete columns. ACMBS-IV, Calgary, Alberta, Canada. 8 pp.

Blontrock, H., L. Taerwe and S. Matthys (1999). Properties of fi bre reinforced plastics at elevated temperatures with regard to fi re resistance of reinforced con-crete members. Fourth International Symposium on Fiber Reinforced Polymer Reinforcement for Concrete Structures, Farmington Hills, MI, pp. 43–54.

Blontrock, H., L. Taerwe and P. Vandevelde (2000). Fire tests on concrete beams strengthened with fi bre composite laminates. Third PhD Symposium, Vienna, Austria. 10 pp.

Brena, S. F., S. L. Wood and M. L. Kreger (2002). Fatigue tests of reinforced polymer composites. Second International Conference on Durability of Fiber Reinforced Polymer (FRP) Composites for Construction, Sherbrooke, Québec, Canada, pp. 575–586.

CAN/CSA-S6-00 (2000). Canadian Highway Bridge Design Code. Rexdale, Ontario, Canadian Standards Association.

CAN/CSA-S806-02 (2002). Design and Construction of Building Components with Fiber Reinforced Polymers. Rexdale, Ontario, Canadian Standards Association.

Chajes, M. J., T. A. Thomson and C. A. Farshman (1995). Durability of concrete beams externally reinforced with composite fabrics. Construction and Building Materials 9(3): pp. 141–148.

Chawla, K. K. (1998). Composite Materials: Science and Engineering. New York, Springer. 483 pp.

CNR (2004). Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Existing Structures, CNR-DT 200/2004. Rome, Italy, CNR – Advisory Committee on Technical Recommendations for Construction. 144 pp.

Coleman, N., U. Khan and Y. K. Gun’ko (2006). Mechanical reinforcement of polymers using carbon nanotubes. Advanced Materials 18: pp. 689–706.

Curtis, P. T. (1989). The fatigue behaviour of fi brous composite materials. Journal of Strain Analysis 24(4): pp. 235–244.

Czaderski, C. (2002). Shear strengthening with prefabricated CFRP L-shaped plates. First fi b Congress, Osaka, Japan.

Czaderski, C. and M. Motavalli (2004). Fatigue behaviour of CFRP L-shaped plates for shear strengthening of RC T-beams. Composites Part B: Engineering 35(4): pp. 279–290.

Czaderski, C. and M. Motavalli (2007). 40-year-old full-scale concrete bridge girder strengthened with prestressed CFRP plates anchored using gradient method. Composites Part B: Engineering 38(7–8): pp. 878–886.

Czaderski, C., K. Soudki and M. Motavalli (2010). Front and side view image correla-tion measurements on FRP to concrete pull-off bond tests. Journal of Composites for Construction, ASCE 14(4): pp. 451–463.

Deuring, M. (ed.) (1994). Brandversuche an Nachträglich Verstärkten Trägern aus Beton. Research Report Empa No. 14’795. Dübendorf, Switzerland, Swiss Federal Laboratories for Materials Testing and Research.

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Devalapura, R. K., M. E. Greenwood, J. V. Gauchel and T. J. Humphrey (1998). Evaluation of GFRP performance using accelerated test methods. First International Conference on Durability of Fiber Reinforced Polymer Composites for Construction, Sherbrooke, Québec, Canada, pp. 107–116.

Dong, Z., U. E. Klotz, C. Leinenbach, A. Bergamini, C. Czaderski and M. Motavalli (2009). A novel Fe–Mn–Si shape memory alloy with improved shape recovery properties by VC precipitation. Advanced Engineering Materials 11(1–2): pp. 40–44.

Eckold, G. (1994). Design and Manufacture of Composite Structures. Cambridge, UK, Woodhead Publishing.

EUROCOMP (1996). EUROCOMP Design Code and Handbook/The European Structural Polymeric Composites Group. London, Spon.

fi b-bulletin-14 (2001). Externally bonded FRP reinforcement for RC structures. Bulletin 14, International Federation for Structural Concrete (fi b), Switzerland. 130 pp.

fi b-bulletin-40 (2007). FRP reinforcement in RC structures. Bulletin 40, International Federation for Structural Concrete (fi b), Switzerland.

FiberlineComposites (2003). Fiberline Design Manual, 2nd edition. Kolding, Denmark, Fiberline Composites A/S.

GangaRao, H. and P. V. Vijay (1997). Aging of structural composites under varying environmental conditions. Non-Metallic (FRP) Reinforcement for Concrete Structures, FRPRCS-3, Sapporo, Japan, pp. 91–98.

GangaRao, H. V. S., N. Taly and P. V. Vijay (2007). Reinforced Concrete Design with FRP Composites. Boca Raton, FL, CRC Press. 382 pp.

Heffernan, P. J. (1997). Fatigue Behavior of Reinforced Concrete Beams Strengthened with CFRP Laminates. PhD thesis, Department of Civil Engineering, Royal Military College of Canada, Kingston, Ontario, Canada, p. 157.

Herakovich, C. T. (1998). Mechanics of Fibrous Composites. New York, John Wiley & Sons.

Hollaway, L. (1993). Polymer Composites for Civil and Structural Engineering. Glasgow, UK, Blackie Academic & Professional. 259 pp.

ISIS-Canada (2001). Strengthening Reinforced Concrete Structures with Externally-Bonded Fibre Reinforced Polymers. Design Manual No. 4. Winnipeg, Manitoba, ISIS-Canada.

ISIS-Canada (2003). An Introduction to FRP Composites for Construction. Winnipeg, Manitoba, ISIS-Canada, www.isiscanada.com.

ISIS-Canada (2006). Durability of fi bre reinforced polymers in civil infrastructure. Retrieved February 2008 from http://www.isiscanada.com.

Janke, L., C. Czaderski, M. Motavalli and J. Ruth (2005). Applications of shape memory alloys in civil engineering structures – Overview, limits and new ideas. Materials and Structures 38(279): pp. 578–592.

Janke, L., C. Czaderski, J. Ruth and M. Motavalli (2009). Experiments on the residual load-bearing capacity of prestressed confi ned concrete columns. Engineering Structures 31(10): pp. 2247–2256.

JSCE (2001). Recommendations for Upgrading of Concrete Structures with Use of Continuous Fiber Sheets. Tokyo, Japan Society of Civil Engineers.

Karbhari, V. M. and I. Eckel (1993). Effect of a Cold-Regions-Type Climate on the Strengthening Effi ciency of Composite Wraps for Columns. Technical Report, University of Delaware, Center for Composite Materials, Newark, NJ, p. 21.

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Karbhari, V. M. and F. Seible (2000). Fiber reinforced composites – Advanced mate-rials for the renewal of civil infrastructure. Applied Composite Materials 7: pp. 95–124.

Karbhari, V. M., M. Engineer and D. A. Eckel (1997). On the durability of composite rehabilitation schemes for concrete: Use of a peel test. Journal of Materials Science 32: pp. 147–156.

Karbhari, V. M., J. W. Chin, D. Hunston, B. Benmokrane, T. Juska, R. Morgan, J. J. Lesko, U. Sorathia and D. Reynaud (2003). Durability gap analysis for fi ber-reinforced polymer composites in civil infrastructure. Journal of Composites for Construction 7(3): pp. 238–247.

Katz, A., N. Berman and L. C. Bank (1999). Effect of high temperature on the bond strength of FRP rebars. Journal of Composites for Construction 3(2): pp. 73–81.

Kim, Y. J., R. G. Wight and M. F. Green (2008). Flexural strengthening of RC beams with prestressed CFRP sheets: Development of nonmetallic anchor systems. Journal of Composites for Construction 12(1): pp. 35–43.

Kodur, V. K. and D. Baingo (eds) (1998). Fire Resistance of FRP Reinforced Concrete Slabs. IRC Internal Report No. 758. Ottawa, National Research Council of Canada.

Kodur, V. K. and L. A. Bisby (2005). Evaluation of fi re endurance of concrete slabs reinforced with FRP bars. Journal of Structural Engineering 131(1): pp. 34–43.

Mander, J. B., M. J. N. Priestley and R. Park (1988). Theoretical stress–strain model for confi ned concrete. Journal of Structural Engineering 114(8): pp. 1804–1826.

Masoud, S., K. A. Soudki and T. Topper (2001). CFRP-strengthened and corroded RC beams under monotonic and fatigue loads. Journal of Composites for Construction 5(4): pp. 228–236.

Meier, U. (1995). Strengthening of structures using carbon fi ber/epoxy composites. Construction and Building Materials 9(6): pp. 341–351.

Meier, U. (2000). Composite materials in bridge repair. Applied Composite Materials 7(2–3): pp. 75–94.

Meier, U. (2007). Is There a Future for Automated Application of CFRP Strips for Post-Strengthening? FRPRCS-8 Symposium, University of Patras, Greece.

Meier, U., M. Deuring, H. Maier and G. Schwegler (1993). Strengthening of struc-tures with advanced composites. In Alternate Materials for the Reinforcement and Prestressing of Concrete, ed. J. L. Clarke. Glasgow, UK, Blackie Academic & Professional, pp. 153–171.

Motavalli, M. and C. Czaderski (2007). FRP composites for retrofi tting of existing civil structures in Europe: State-of-the-art review. ACMA, Tampa, FL, 17–19 October, 2007.

Motavalli, M., C. Czaderski, A. Bergamini and L. Janke (2009). Shape memory alloys for civil engineering structures – on the way from vision to reality. ACEE Journal, Architecture Civil Engineering Environment, The Silesian University of Technology, Poland 2(4): pp. 81–94.

Motavalli, M., C. Czaderski and K. Pfyl-Lang (2010). Prestressed CFRP for strength-ening of reinforced concrete structures – Recent developments at Empa Switzerland. Journal of Composites for Construction, ASCE (online 6.4.2010): doi10.1061/(ASCE)CC.1943-5614.0000125.

Mufti, A. A., M. Onofrei, B. Benmokrane, N. Banthia, M. Boulfi za, J. Newhook, B. Baidar, G. Tadros and P. Brett (2005). Durability of GFRP reinforced concrete

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in fi eld structures. Third International Conference on Composites in Construction, Lyon, France, pp. 889–895.

Nanni, A., C. E. Bakis and T. E. Boothby (1995). Test methods for FRP-concrete systems subjected to mechanical loads: State of the art review. Journal of Reinforced Plastics and Composites 14: pp. 524–558.

Odagiri, T., K. Matsumoto and H. Nakai (1997). Fatigue and relaxation char-acteristics of continuous aramid fi ber reinforced plastic rods. Non-Metallic (FRP) Reinforcement for Concrete Structures, FRPRCS-3, Sapporo, Japan, pp. 227–234.

Papakonstantinou, C. G., M. F. Petrou and K. A. Harries (2001). Fatigue of reinforced concrete beams strengthened with GFRP sheets. Journal of Composites for Construction 5(4): pp. 246–253.

Plevris, N. and T. C. Triantafi llou (1994). Time-dependent behaviour of RC members strengthened with FRP laminates. Journal of Structural Engineering 120(3): pp. 1016–1042.

Porter, M. L. and B. A. Barnes (1998). Accelerated aging degradation of glass fi ber composites. Second International Conference on Composites in Infrastructure, University of Arizona, Tucson, AZ, pp. 446–459.

Quattlebaum, J., K. A. Harries and M. F. Petrou (2005). Comparison of three CFRP fl exural retrofi t systems under monotonic and fatigue loads. Journal of Bridge Engineering 10(6): pp. 731–740.

Rizkalla, S. and T. Hassan (2002). Effectiveness of FRP for strengthening concrete bridges. Structural Engineering International 12(2): pp. 89–95.

Rostasy, F. S. (1997). Durability of FRP in aggressive environments. Non-Metallic (FRP) Reinforcement for Concrete Structures, FRPRCS-3, Sapporo, Japan, pp. 113–128.

Saafi , M. (2002). Effect of fi re on FRP reinforced concrete members. Composite Structures 58: pp. 11–20.

Schwegler, G. (1994). Verstärkten von Mauerwerk mit Faserverbundwerkstoffen in seismisch gefährdeten Zonen. Dübendorf, Switzerland, Empa Dübendorf, Report no. 229.

Sen, R., M. Shahawy, S. Sukumar and J. Rosas (1998). Durability of carbon preten-sioned elements in a marine environment. ACI Structural Journal 95(6): pp. 716–724.

Shahawy, M. and E. T. Beitelman (1999). Static and fatigue performance of RC beams strengthened with CFRP laminates. Journal of Structural Engineering 125(6): pp. 613–621.

Sheard, P. A., J. L. Clarke, M. J. U. Dill, G. P. Hammersley and D. M. Richardson (1997). Eurocrete – Taking account of durability for design of FRP reinforced concrete structures. Non-Metallic (FRP) Reinforcement for Concrete Structures, FRPRCS-3, Sapporo, Japan, pp. 75–82.

SIA166 (2004). Klebebewehrungen (Externally Bonded Reinforcement). Schweizerischer Ingenieur- und Architektenverein SIA. 44 pp.

SIA262 (2003). Swisscode: Betonbau (Concrete Structures). Schweizerischer Ingenieur- und Architektenverein SIA. 90 pp.

Smith, S. T. and J. G. Teng (2001). Interfacial stresses in plated beams. Engineering Structures 23(7): pp. 857–871.

Sorathia, U., T. Dapp and C. Beck (1992). Fire performance of composites. Materials Engineering 109(9): pp. 10–12.

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Soudki, K. A. and M. F. Green (1996). Performance of CFRP retrofi tted concrete columns at low temperatures. Second International Conference on Advanced Composite Materials in Bridges and Structures, Montreal, Canada, pp. 427–434.

Spoelstra, M. R. and G. Monti (1999). FRP-confi ned concrete model. Journal of Composites for Construction 3(3): pp. 143–150.

Takewaka, K. and M. Khin (1996). Deterioration of stress-rupture of FRP rods in alkaline solution simulating as concrete environment. Second International Con-ference on Advanced Composite Materials in Bridges and Structures, Montreal, Canada, pp. 649–664.

Teng, J. G., J. F. Chen, S. T. Smith and L. Lam (2002). FRP: Strengthened RC Structures. Chichester, UK, John Wiley & Sons. 245 pp.

TR55 (2000). Design Guidance for Strengthening Concrete Structures Using Fibre Composite Materials. Crowthorne, Berkshire, UK, The Concrete Society.

TR55 (2004). Design Guidance for Strengthening Concrete Structures Using Fibre Composite Materials, second edition. Crowthorne, Berkshire, UK, The Concrete Society, 102 pp.

Triantafi llou, T. C. (1998). Shear strengthening of reinforced concrete beams using epoxy-bonded FRP composites. ACI Structural Journal 95(2): pp. 107–115.

Triantafi llou, T. C. and C. P. Antonopoulos (2000). Design of concrete fl exural members strengthened in shear with FRP. Journal of Composites for Construction 4(4): pp. 198–205.

Wan, B., K. A. Harries, M. F. Petrou, M. A. Sutton and N. Li (2003). Experimental investigation of bond between FRP and concrete. 2003 SEM Annual Conference, Charlotte, VA. 6 pp.

Williams, B. K. (2004). Fire Performance of FRP-Strengthened Reinforced Concrete Flexural Members. PhD thesis, Department of Civil Engineering, Queen’s University, Kingston, Ontario, Canada, p. 389.

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129

5Developing and testing textiles and coatings

for tensioned membrane structures

T. STEGMAIER, P. SCHNEIDER, A. VOHRER and H. PLANCK, Institute of Textile Technology and Process Engineering Denkendorf (ITV), Germany and R. BLUM and H. BÖGNER-BALZ, Laboratorium

Blum, Germany

Abstract: Textiles have become fi rmly established in the construction industry, e.g. as membrane structures for roofi ngs. For such types of buildings, comprehensive knowledge of the materials regarding their strength under static and dynamic stresses, their durability and their differing environmental impacts is essential. The behaviour of the material depends on its structure, whether made of fi bres, yarns, fabrics, coatings, laminates or multilayer systems. In this chapter the most important test methods are described for mechanical, chemical, cleaning and durability properties with an overview of the most important standards. Depending on the light transmission and light refl exion the energy management is evaluated.

Key words: tension, strength, elongation, biaxial test, static and dynamic stress, durability, environmental impact, material behaviour, connecting systems, coatings, laminates, multilayer systems, test methods, standards, fl ammability, light transmission, light refl exion, energy management.

5.1 Introduction

Textile architecture combines creativity and elegance with economical material consumption, short construction periods and comparatively low costs. Textiles have become fi rmly established in the construction industry, e.g. as membrane structures for roofi ngs. This domain of the building indus-try is the only one that shows an above-average growth. For such types of buildings, comprehensive knowledge of the materials regarding their strength under static and dynamic stresses, their durability and their differ-ing environmental impacts is essential.

5.2 Material systems used for membranes

Textile building materials consist of fi bres, assembled into linear structures such as threads or ropes, and area-measured materials such as nets.

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Generally the fi bres are protected by a polymeric coating, which in addition enables the membrane to have a barrier function against the environment (light, wind, rain, fi re, etc.). Textile membranes for building construction are available in many varieties and in different qualities. In the following a selection of the main products available on the market today will be described.

5.2.1 Fibres and fabrics

Cotton, polyamide, polyester, glass fi bre, aramids, carbon fi bres, fl uoro-polymer fi bres (polytetrafl uoroethylene (PTFE), polyvinylidene fl uoride (PVDF), ethylene-tetrafl uoroethylene (ETFE)) and metal wires can all be used as fi bre materials.

Pure cotton is not used for sophisticated structures because of its poor tensile strength, its elasticity and its vulnerability to microbial attack and the resulting biological degradation. Today pure cotton is only used for leisure tents and indoor applications.

PTFE fi bres are used as tapes, but can only be laminated with fl uorinated polymers. They have a long life-span, high chemical resistance, very good soiling behaviour and translucency.

Aramids have the highest tensile strength. They show very good chemical and thermal resistance but low elasticity and poor UV resistance. Poly-ethylene terephthalate (PET) fi bres, a thermoplast from the polyester family, show good tensile strength and elongation at break. Their mechani-cal properties are degraded by UV radiation but this can be avoided by a protective coating.

Glass fi bres show very high tensile strength but are brittle and have a small elongation at break. Carefully handled and manufactured, they are resistant to chemical infl uences and ageing. When glass is exposed to humidity it is hydrolysed and loses strength. To protect glass fi bres from humidity, they are impregnated with a special size subsequent to spinning and are therefore additionally coated.

In general, PET with a high tensile strength, and glass, which both appear as multifi lament yarns, are used for coated membranes. For load-bearing constructions woven fabrics are mostly qualifi ed: twisted multifi laments are processed to plain woven fabrics in plain or in panama weave.

5.2.2 Coating materials

The fabrics are coated for protection with polymeric materials. Most common are

• Polyvinyl chloride (PVC)• Polytetrafl uoroethylene (PTFE)

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Developing and testing textiles and coatings 131


• Polymers related to it (PVDF, ETFE)• Silicone rubbers.

The coating on both sides protects the fabric against humidity, radiation and ageing and enables thermoplastic polymers for welding in the manu-facturing process.

Because PVC has been used for membrane structures since the 1950s, and PTFE since the 1970s, their long-term behaviour is well known and their processing technology is being improved continuously. PVC itself is brittle and shows low UV resistance. To avoid this, plasticizers and stabiliz-ing additives are added. PVC coatings have high tensile strength, elasticity and bending strength. A minimum of 15 years’ life-span can be guaranteed. Recycling presents some problems because PVC contains halogens. PTFE shows the best chemical and ageing resistance of all polymers. A life-span of more than 30 years can be achieved. Due to the high processing tem-peratures (up to 400°C) during coating, PTFE can only be coated on glass or PTFE fi bres, but not on PET fi bres.

Silicone rubbers are elastomeric and three-dimensionally crosslinked polymers. They are smooth in bending and have a high compliance in tension even at very low temperatures. Their chemical properties are com-parable to those of PTFE. Silicone coatings need only low coating tempera-tures which would enable coating not only on glass but also on PET fi bres.

Under development are coatings based on thermoplastic processing such as thermoplastic polyurethane (TPU). The future will show whether PU coatings are competitive in joining, durability, translucency and economy compared to PVC or PTFE ones.

Instead of a coating, sometimes foils are laminated onto the fabric.

5.2.3 Composites: coated textiles

Because of their favourable cost–performance ratio, polyvinyl chloride (PVC) coated polyester (PET) fabric is the most common basic material used. It can be applied over the whole spectrum from small temporary to wide-span structures. With a top-coat that protects the PVC from soiling and early ageing, a life-span of up to 20–25 years can be obtained. PVC–PET composites are joined by high-frequency or hot wedge welding. With fl ame-retardant additives to the PVC coating, fi re class B1 can be achieved.

Polytetrafl uoroethylene (PTFE)-coated glass fi bre fabrics are character-ized by high chemical and UV resistance. A life-span of more than 30 years can be achieved. Due to the residual stresses of glass fi bres and the bending stiffness of the PTFE-coating, PTFE-coated glass fi bre fabrics need to be handled with care. Hence PTFE-coated glass fabric is only suitable for permanent non-folding structures. A PTFE-coated fabric can achieve light translucency of 13%, open mesh composites up to 65% – but at the expense

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of strength and watertightness. For higher translucency, PTFE or ETFE fi lms laminated on glass fi bre meshes or PTFE fabrics are available. The shear stiffness is a characterizing parameter for the design of three-dimensional structures made of two-dimensional blanks. PTFE–glass com-posites have a higher shear stiffness than PET–PVC fabrics.

At the beginning silicone rubber-coated glass fi bre fabrics were used in very few projects for textile architecture because of their high tendency to soiling. But since then easy-cleaning top-coats have become available for silicone rubbers. If coated on PET fabric, which is in development at the moment, they show better bending behaviour and could be used for tempo-rary or retractable constructions. Furthermore, silicone rubber composites have a translucency of more than 20%. Silicone rubber and PTFE–glass composites can achieve fi re class A2. Due to their very good performance, better waste management and the fact that they are easier to produce, sili-cone rubbers could become a cost-saving alternative for PTFE composites.

5.3 Test methods and characterization of membranes

5.3.1 Introduction

Membrane materials are fl exible and only stabilized by tension. Therefore the most important mechanical parameters for construction are tensile strength and elastic properties. It is essential to distinguish between stiff-ness and strength (with and without deterioration).

A high quality standard requires test certifi cates such as for tensile strength and coating adhesion, chemical properties such as hydrolysis resis-tance and optical properties such as UV, VIS and IR transmission. Furthermore, certifi cates for all kinds of resistance such as fi re protection and ageing stability are also required.

Multilayered membrane constructions have advantages in functionality, but they must be certifi ed in their physical functionality in the complete construction system. We note that there is a particular problem concerning in-layered condensate.

Further material characteristics for declaration and control of sustain-ability of the membranes are required. They are based on analyses of maintenance, repair and recycling.

5.3.2 Authorization

The following sections provide the basic knowledge to obtain authorization for membranes for building with textile materials. This takes account of the EU Building Products Guidelines, which are also valid in Germany in the form of the law dated 28 April 1998, updated on 15 December 2001.

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Additional items have to be considered: the German Model Building Regulations and the National Building Regulations insofar as they contain supplementary requirements on this subject. The standard to be observed is DIN 18200.

This chapter presents one option for approval testing. It is left to the applicant to carry out any further optional testing or to try out other methods, since in this area there are not many standards. Therefore this procedure is written up according to Section B of the Building Products Guidelines. The considerations we have laid out here are ideal for high-quality Type III PVC-coated polyester fabrics. It is certainly possible to transfer this procedure to other types of fabric but then it would be neces-sary to discuss the individual details again.

To start off, the basis documents for the Building Products Guidelines are listed. Six basis documents have been defi ned:

• Basis document 1: Mechanical strength and structural stability• Basis document 2: Fire protection• Basis document 3: Hygiene, health and environmental protection• Basis document 4: Operating safety• Basis document 5: Sound protection• Basis document 6: Energy-saving and thermal protection.

All the bold printed documents are relevant to membranes. Thereby the roles of basis documents 1, 2, 5 and 6 are clear. The role of basis document 3, however, must be explained in a little more detail. In the case of high air humidity levels there is the problem of the PVC being affected by moulds. This has to be counteracted by means of suitable additives. This effect has to be investigated. In addition, over a long period of time the membrane will become contaminated. To prevent contamination, precautions with a so-called top-coat can be taken. Here again the soiling behaviour has to be investigated.

Sound protection requires special consideration, as described in more detail below. For basis document 6 we include light, since light is directly involved with energy.

The tests described in the following have to be classifi ed as:

• Tests required for the initial approval of the coating fi rm• Tests required for the self-monitoring of the coating fi rm• Tests required for the external monitoring of the coating fi rm• Tests required for the initial monitoring of the fabric manufacturer• Tests required for the self-monitoring of the fabric manufacturer• Tests required for the external monitoring of the fabric manufacturer.

In addition, within the scope of the authorization required from the Building Inspection Authorities, it is necessary to defi ne:

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• The evidence of identity• Reduction factors.

5.4 Mechanical tests and behaviour of membranes

Mechanical strength and stiffness are essential properties needed for design and construction. Another property which might be taken into account for the design of membrane structures is the tear resistance. The polymer coating infl uences the tear propagation resistance as well as the bending fatigue strength. The coating fi xes the warp and weft threads within the fabric and increases the stiffness of the membrane. The adhesion of the coating to the fabric also is an indicator of the seam resistance. The uniaxial tensile test gives an idea of the tensile strength of the material and details, but no information on the deformation behaviour in the working range. The tear propagation test is used to fi nd the carrying capacity.

A fi nite element calculation with computer technologies is used to lay out the mechanical conditions, such as tension and deformation. Therefore, it is practicable to use the biaxial tension test. This test offers the possibility of drawing the deformation corresponding to the load cases in the direction of the fi bre. In addition to these static tensile tests, high-level biaxial tensile testing machines are used for dynamic tests. These are used to describe the fatigue behaviour of the membrane for heavy wind loads using in-plane and out-of-plane mechanical loads to simulate fl agging. It is known that the deformation behaviour of membrane materials consists of elastic and plastic deformation. However, the plastic deformation is a function of time. Therefore a long-duration tensile test is used to describe the time-dependent plastic deformation of membrane materials, which is also known as creep under tension.

5.4.1 Biaxial machine

In the design stage of a new membrane roof, several properties of the mate-rial from which the roof will be built need to be determined experimentally. For dimensioning, the Young’s modulus has to be known, and for the cutting pattern the compensation values have to be defi ned. Both of these values can be measured in a biaxial test using the loads of the respective project.

Labor Blum has developed a biaxial machine (Fig. 5.1) which in our opinion is of the right size to obtain a homogeneous stress fi eld that is large enough for an exact measurement. The overall dimensions of this biaxial machine are 2.44 × 2.44 m2, and the planar two-dimensional test sample measures about 1.10 × 1.10 m2.

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The force is induced to the sample via clamps and straps. On every side of the square sample, seven straps are fi xed in clamps that are attached via force measurement rings to low-friction ball screws which are driven by altogether 28 servo motors. Each servo motor is controlled independently. The servo motors are able to move perpendicularly to the force direction. The force is applied independently and uniaxially into every strap. To control the servo motors it is necessary to provide a control output variable for the force in the spindle. This must then be measured with a resolution better than 1%. Therefore the force measuring rings we use have been developed by ourselves. The biaxial measurement fi eld has dimensions of 0.70 × 0.70 m2, and loads of up to 200 kN/m can be applied. Strains are measured with potentiometric sensors. The external control circuit is set up digitally by means of a PC.

This machine has been developed in an EC project by Labor Blum (Stuttgart, Germany) in cooperation with IF (Constance, Germany), Ferrari (La Tour du Pin, France) and Audra (Friedberg, Germany).

5.4.2 Overview of mechanical strength and structural stability

The evidence required of the mechanical strength and structural stability can be subdivided into areas that are discussed in the following sections:

5.4.3 Determination of the strength of the material Short-term strength behaviour Long-term strength behaviour5.5 Strength of the connecting systems for membranes 5.5.1 Short-term behaviour of welded seams 5.5.2 Long-term behaviour of welded seams

5.1 Biaxial machine of Labor Blum with climatic chamber from −20°C up to 70°C.

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5.5.3 Clamped connections Short-term behaviour of a clamped seam Long-term behaviour of a clamped seam 5.5.4 Pocket edges: tubular and cable edges Short-term behaviour Long-term behaviour 5.5.5 Deformation behaviour Biaxial, parallel thread tests Shear behaviour Determination of shear modulus Relaxation behaviour Creep

5.4.3 Determination of the strength of the material

Short-term strength behaviour

Normally, strength investigations for standard and technical textiles are carried out as single-axis strip tests. In this way it is only the single-axis strength which can be established with loads parallel to the threads. In general it is assumed that with a twin-axis load the strength will be lower than with a single-axis load. For this reason a reduction factor is inserted, which is not determined but rather simply is assumed.

The twin-axis strength is very diffi cult to measure: in a twin-axis testing unit which is familiar, it is the strength of the sample and not that of the material that is determined, as the failure always starts from the edge.

Another method would be the examination of a cylinder which is loaded by a compressive force as well as axial loads. In the production of a cylinder, however, a seam is necessary, at which point this sample body could also tear. A way out of this would appear to be the bursting test which is pro-posed in the standards, but which will fi rst have to be examined more closely.

Corresponding tests are being prepared. We will start here with the description of the single-axis tests.

Single-axis strip strength with loading parallel to the thread

In the strip test (Fig. 5.2) the strength of a 10 cm wide strip of fabric cut parallel to the warp and parallel to the weft is proposed as in DIN 53354, DIN 13934-1 and other standards. In setting the number of tests it is neces-sary to decide which evaluations are the most important:

• If only the average is to be given then normally only fi ve tests are suffi cient.

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• If, however, more accurate information on the distribution of measured values is to be given, for example to calculate the 5% fractile, then signifi cantly more tests are required.

• If, however, the 5% fractile can be given safely, this value can then be used to establish a reduction factor for the inhomogeneity of the fabric.

It is also necessary to note that the strength can depend on from where the sample has been removed. On the edge of the web, for example, lower strengths are often measured more often than those in the middle. Measurements taken at the start of a roll can also turn out to be lower than in the middle. It is therefore necessary to prepare a sampling plan to inter-pret any non-homogeneous strength distributions.

It is necessary to give individual breaking test results, type of break, width of strip, breaking stress, average value, standard deviation, 5% frac-tile, and sample removal plan. If possible, the elongation should be mea-sured at the same time to comment on any differences in the elongation behaviour. Such a device can only operate on an optical base and must not be a device which involves contact, otherwise the measuring equip-ment can be destroyed. If characteristic subsets are found in the results that can be traced back to the sampling plan, then such subsets will have to be treated as separate statistics, since otherwise they would falsify the statistics.

5.2 Strip test.

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The test should be carried out at different temperatures: 23°C, 70°C and −20°C.

Tests at 23°C:Test procedure: According to DIN 53354, ISO 1421 (DIN

13934-1) with the alteration that the width of the sample must be 100 mm

Test type: Initial approval, self-monitoring, external monitoring

Duty to provide evidence: Coating fi rmTest quantity: At least fi ve in each direction, warp and weftInitial test: Twenty warps, 20 wefts for 23°Self-monitoring: Ten warps, 10 wefts per batchExternal monitoring: Visit twice per annum, removal of a 2 m wide

piece at a random interface, 10 warp tests, 10 weft tests

Tests at 70°C:Here – with equal test settings – the above-mentioned description also applies, with the supplementary requirement that the samples must be brought up to the testing temperature for at least one hour before testing and that the clamps must also be at the sample temperature if at all possible.

Note that for a PVC-coated polyester fabric 70°C can be reached without any problems. For other fabrics, however, other testing temperatures have to be used, so that under the effect of the sun’s rays they do not heat up too much. Until there is evidence of lower testing temperatures, however, 70°C should be set. The evidence of lower testing temperatures can be determined either by calculation using the absorption curves for radiation or by means of tests.

Test procedure: According to DIN 53354, ISO 1421 (DIN 13934-1) with the alteration that the width of the sample must be 100 mm

Test type: Initial approval, self-monitoring, external monitoring

Duty to provide evidence: Coating fi rmTest quantity: At least fi ve in each direction, warp and weftInitial approval: Twenty warp samples, 20 weft samplesSelf-monitoring: Five warp samples, fi ve weft samples per batchExternal monitoring: Five warp samples, fi ve weft samples, for

removal see above

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Tests at −20°C:Here again – with equal test settings – the above-mentioned applies. The test does not have to be carried out if the application is not expected to reach these temperatures.

Test procedure: According to DIN 53354, ISO 1421 (DIN 13934-1) with the alteration that the width of the sample must be 100 mm

Test type: Initial approvalDuty to provide evidence: Coating fi rmTest quantity: Twenty warp samples, 20 weft samples

Biaxial strength

In addition to the strip tests, two-dimensional bursting tests should be carried out for the initial approval. The diffi culties in carrying out bursting tests occur because the fabrics are anisotropic materials. This also means that the deformation shape only approximates to a calotte (clam) shell and the determination of the failure load has many elements of uncertainty. The problem has to be investigated further in future scien tifi c work.

Test procedure: Bursting test according to DIN 53861 with a circle diameter of 500 mm

Test type: Initial approvalDuty to provide evidence: Coating fi rmTest quantity: To be established according to the spread of the

tests but at least three

Tear strength

As the last variable in this list of materials, the tear strength has to be mentioned. First the basic task for this test has to be defi ned: A membrane has a tear-type damage of a defi ned length. Required is the load at which the tear will be subject to unstable spread so that the membrane fi nally fails. The theory here is that of fracture mechanics, in which the stress concentra-tion factor is defi ned as the decisive variable. This material variable is defi ned on the basis of the linear theory of elasticity and can be applied to anisotropic materials without any problems. It shows that this theory is also valid as a good approximation for coated fabrics.

The corresponding twin-axis tests are sketched in Fig. 5.3.

Evaluation method biaxial tear tests

The evaluation should be done according to linear-elastic fracture mechan-ics where a stress concentration factor Kc is defi ned as follows:

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K ac = π σ 5.1

where a = half of the slit length, and σ = stress perpendicular to the slit direction ad infi nitum.

It has been proven that this procedure can be applied on anisotropic fabrics with an appropriate accuracy. The stress concentration factor is a material constant from which can be calculated either at which stress level a slit with a certain length is going to propagate or how long a slit could be that would stay stable at a certain stress level. For the formulation of a reduction factor we suggest starting with a slit of 5 cm and considering the stress at which the tear starts to propagate.

Biaxial tear test:Test procedure: According to LBV P1111Evaluation: According to LBV P1111 (see above)Test type: See commentsDuty to provide evidence: See commentsComments: Whether a time-consuming tear growth test is

really part of the approval process still has to be discussed. Normally textile structures are not at risk of tearing after the erection

Single-axis tear propagation test:Test procedure: DIN 53363Evaluation: See standardTest type: Initial approval, external monitoringDuty to provide evidence: Coating fi rm

5.3 Biaxial tear test with a cut in the middle of the fi eld.

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Test quantity: At least fi ve in each direction, warp and weftInitial approval: Ten warp samples, 10 weft samplesExternal monitoring: Five warp samples, fi ve weft samples

In the textile industry the trapezoidal test has become well established for this purpose, since it is easy to carry out and is subject to DIN stan-dard 53363. However, this test can only be used as a comparison test between different fabrics. Therefore no conclusion on the tear strength can be drawn from this test. It is not recommended if the test defi ned above has been accepted. The references here are only included for the sake of completeness.

Test procedure: According to DIN 53363Comments: This test is not recommended, since its evaluation provides

no information on the tear strength

Long-term strength behaviour

Strength loss following loading

The long-term strength behaviour test is carried out in the same way as the short-term strength test, namely in single-axis strip tests parallel to the threads (see the tests at 23°C on page 138). Load steps should be set at 10%, 20%, 50% and 90% of the short-time tensile strength. Ten samples are required to be tested for each load step. After 1000 hours the residual strength is established.

A series of tests have to be done in order to achieve a sensitive reduction factor for long-term loading.

Test: After single-axis loading at 23°C over 1000 hours, single axis strength according to the tests at 23°C or 70°C on page 138

Test type: Initial testDuty to provide evidence: Coating fi rmTest quantity: At least three samples for each load in the warp

direction and three in the weft direction

Strength loss due to exposure to weather

After the pure loading tests artifi cial weathering tests are also required. In these weather exposure tests strips taken in the warp and weft directions are subjected to a standard climate. The exposure time is normally 1000 hours. After this time the strengths are determined. A time acceleration factor of 10 can be achieved. In other words, after 1000 hours of artifi cial weathering the strength loss after 10,000 hours can be determined. Alongside this are also calculation methods for the determination of the loss of

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strength, which are based on a lengthy series of tests. Calculation models for the prediction of this behaviour are in development.

5.5 Strength of the connecting systems

for membranes

5.5.1 Short-term behaviour of welded seams

Seam strengths in uniaxial tests parallel to the threads

Normally the fabric manufacturer is responsible for the seam and its strength. On the other hand, the seam strength to a great extent depends on the bonding strength of the coating on the fabric, for which the coating company is responsible. Thus there is a split responsibility here. The con-sequences of this can be explained as follows. The coating company shows what can be achieved by optimizing its technology of bonding the coating onto the fabric. To achieve this, prototype trials are necessary. In these trials the achieved seam strength has to be established and proven. For this purpose the following tests are required. The strength of the seam with various seam widths is determined. Then the seam width is increased up to the point where no more increase in strength is determined. This permits the defi nition of an optimum seam width. Up to this optimum seam width the strength increases linearly with the width. From this dependency and knowing the optimum width, it is then possible to determine the minimum seam width, which permits the establishment of the attainable seam strength depending on the width. It remains to be said that other seam versions such as in Fig. 5.4 can lead to higher seam strengths. This should not, however, be the subject of a general approval process but should have to be proven in the individual cases. Two tests are discussed below.

Determination of an optimum seam width at 23°C for seam widths less than the optimum

Determination of the dependency of the strength on the seam width at 23°C:

Test procedure: DIN 53354 / ISO 1421 and LBVTest type: Initial approvalDuty to provide evidence: Coating fi rm, fabric manufacturerTest quantity: At least fi ve in each direction, warp and weftInitial approval: Twenty samples in warp direction, 20 samples

in weft direction for both the coating fi rm and the fabric manufacturer

The fabric manufacturer now has to prove whether he can achieve the strength which has been reached and proven by the coating fi rm or whether he has to make concessions. Accordingly he has to establish his seam width

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and defi ne and prove the corresponding strength. Figure 5.4 shows failure resulting from the seam test.

Determination of seam strength at 23°C at the seam width established by the fabric manufacturer:

Test procedure: DIN 53354 / ISO 1421Evaluation: According to DINTest type: Initial approval, self-monitoring, external

monitoringDuty to provide evidence: Fabric manufacturerTest quantity: At least fi ve in each direction, warp and weftInitial approval: Twenty samples in warp direction, 20 samples

in weft directionSelf-monitoring: Five samples in warp direction, fi ve samples in

weft direction per 1000 m2 of fabricExternal monitoring: Ten samples in warp direction, 10 samples in

weft direction

Seam strengths at −20°C and 70°C

Here it is only necessary to carry out parallel-thread single-axis tests. All other things being equal, the proposals outlined above can be used. Twin-axis tests are not required here.

5.4 Seam test, failure.

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Test procedure: DIN 53354 / ISO 1421Evaluation: According to DINType of test: Initial approval, external monitoringDuty to provide evidence: Fabric manufacturerTest quantity: At least fi ve in each direction, warp and weftInitial approval: Ten samples each in warp direction, 10 samples

each in weft directionExternal monitoring: Inspection visits twice per annum, removal of a

2 m wide piece from a random interface, manu-facture of the seam, 10 warp tests, 10 weft tests

Biaxial seam strength/bursting test

So far the determination of the seam strength has been suitably defi ned. It is now necessary to ensure that there are no membrane structures that only have seams where the seam direction is parallel to the warp and weft. Especially in the case of seams where the warp lies approximately over the warp direction, it is necessary to provide even a small angle between these two directions. In the general situation this angle will be reduced as dis-cussed later. The strength of the seam will be dependent on this angle so this value should be determined. However, it cannot be established in single-axis tests since in this case shear distortions will occur which do not occur in practice. This strength can therefore only be measured in twin-axis stresses. The standard twin-axis tests, however, nearly always result in a failure starting from the edge. Therefore it is really only the sample shape that is being tested and not the seam.

The bursting test is capable of answering the question of the twin-axis strength. Therefore the bursting test is required here. The diameter of the base circle should be at least fi ve times the seam width. The results of the bursting tests will establish the reduction factor of the parallel single-axis seam test as a result of twin-axis loading.

Test procedure: According to DIN 52861-3Evaluation specifi cations: Still to be preparedType of test: Initial approvalDuty to provide evidence: Coating fi rm, fabric manufacturerTest quantity: To be established according to initial tests

5.5.2 Long-term behaviour of welded seams

Behaviour according to load

The strength in long-term behaviour is established exactly as for short-term strength in single-axis tests parallel to the threads. The following loading steps are used:

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• Pre-stress• Working stress• Mean value of pre-stress and working stress• 75% of the sum of pre-stress and working stress• 25% of the sum of pre-stress and working stress.

Ten samples are tested for each load step. After 1000 hours the residual strength is then established. Pre-stress and working stress are defi ned above with respect to the strength.

Test: Single-axis strength after single-axis loading at 23°C over 1000 hours

Test type: Initial testDuty to provide evidence: Fabric manufacturerTest quantity: Three samples for each load in the warp direc-

tion and three in the weft direction

Strength reduction after exposure to weather

Besides the pure loading tests, artifi cial weathering tests are also required. In these weather exposure tests strips taken in the warp and weft directions are subjected to a standard climate. The exposure time is normally 1000 hours. After this time the strengths are determined. A time acceleration factor of 10 can be achieved. In other words, after 1000 hours of artifi cial weathering the loss of strength after 10,000 hours can be determined.

Alongside this are also calculation methods for the determination of the loss of strength based on a lengthy series of trials. At present these calcula-tions are undergoing formalization.

5.5.3 Clamped connections

Short-term behaviour of a clamped seam

In a clamped seam the two edges to be joined together are provided with a piped edge and then perforated at a defi ned spacing. The two edges are then screwed together with clamping plates as shown in Fig. 5.5 so that the piping lies within the clamping plates and the force is transferred at that point. The pressing force of the clamping plates cannot be too high so that the force to be transferred only passes into the membrane by fric-tion, as the strength of the thread is reduced. The piping material must not be too soft so that due to the membrane tension it is drawn through the piping clamps. It is necessary to consider that temperatures of −20°C up to +70°C can arise. For this reason the piping material used should never be soft PVC, but rather an elastomeric material which has the respec-tive temperature resistance. The pressing force is produced by screws and

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for these screws the clamping plates have to be drilled and the membrane perforated. The hole spacings should be matched up with one another in the pre-stressed condition. For this purpose the spacings must be compen-sated for.

The stress distribution in the area around the hole demonstrates a stress concentration through which stress singularities can affect the membrane. These must not lead to failure, therefore part of the arising membrane forces should be taken up by friction which results from compression. The hole spacings must not be so small that these singularities on top of the other forces could lead to damage.

In the pre-stressed condition the membrane pulls slightly into the clamps. Because of this it is possible that the hole face could be forced against the clamping screw and damage may be induced at this point as a result. The hole in the membrane, therefore, always has to be somewhat bigger than the screw which passes through.

The evidence for this connection is the task of the fabric manufacturer. He has to prove the strength. The evidence can be derived from a single-axis strip test parallel to the threads with a single-axis tensile load. The corresponding test can be described as follows.

Determination of the strength of a clamped seam in a uniaxial test, parallel to the threads at 23°C, 70°C and −20°C.

Tests at 23°C:Test procedure: According to DIN 53354 / ISO 1421, similar to

the single-axis seam testEvaluation: See aboveType of test: Initial approval, self-monitoringDuty to provide evidence: Fabric manufacturerTest quantity: At least fi ve in each direction, warp and weftInitial approval: Ten strips in the warp direction, 10 strips in the

weft directionSelf-monitoring: Five tests per 1000 m of continuous clamped

seam

Tests at 70°C:Test procedure: According to DIN 53354 / ISO 1421, similar to

the single-axis seam testEvaluation: See aboveType of test: Initial approval, self-monitoringDuty to provide evidence: Fabric manufacturerTest quantity: At least fi ve in each direction, warp and weftInitial approval: Ten strips in the warp direction, 10 strips in the

weft direction

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Self-monitoring: Five tests per 1000 m of continuous clamped seam

Tests at −20°C:Test procedure: According to DIN 53354 / ISO 1421, similar to

the single-axis seam testEvaluation: See aboveType of test: Initial approvalDuty to provide evidence: Fabric manufacturerTest quantity: Ten strips in the warp direction, 10 strips in the

weft direction

Determination of the strength of a clamped edge at 23°C, 70°C and −20°C

For this purpose the above-mentioned description for the clamped seam can be used – everything else has been retained unchanged. The test required (for detail see Fig. 5.5) is once more the single-axis, parallel-thread strip test. As mentioned above, it is essential to ensure that the clamps, etc., are also brought up to the testing temperature.

At 23°C:Test procedure: According to DIN 53354 / ISO 1421, similar to

the single-axis seam test

5.5 Detail of clamped edge test.

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Evaluation: See aboveType of test: Initial approval, self-monitoring, external

monitoringDuty to provide evidence: Fabric manufacturerTest quantity: At least fi ve in each direction, warp and weft

At 70°C:Test procedure: According to DIN 53354 / ISO 1421, similar to

the single-axis seam testEvaluation: See aboveType of test: Initial approvalDuty to provide evidence: Fabric manufacturerTest quantity: At least fi ve in each direction, warp and weft

At −20°C:Test procedure: According to DIN 53354 / ISO 1421, similar to

the single-axis seam testEvaluation: See aboveType of test: Initial approvalDuty to provide evidence: Fabric manufacturerTest quantity: At least fi ve in each direction, warp and weft

Long-term behaviour of a clamped seam

No tests are anticipated for the long-term behaviour of clamped connections.

5.5.4 Pocket edges: tubular and cable edges

Short-term behaviour

Tubular edge at −20°C, 23°C and 70°C:Test procedure: According to DIN 53354 / ISO 1421, similar to

the uniaxial seam testEvaluation: See aboveType of test: Initial approval, self-monitoring, external

monitoringDuty to provide evidence: Fabric manufacturerRemarks: It is essential to ensure that the cable remains

straight during the test and is not bent as other-wise another form of failure will occur

Cable edge at 23°C (see Fig. 5.6):Test procedure: According to DIN 53354 / ISO 1421, similar to

the single-axis seam test

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Evaluation: See aboveType of test: Initial approval, self-monitoring, external

monitoringDuty to provide evidence: Fabric manufacturer

Long-term behaviour

No tests on the long-term behaviour of pocket edges have been proposed.

5.5.5 Deformation behaviour

Biaxial, parallel thread tests

Twin-axis tests are not intended for measuring strengths, but to establish the compensation data and to determine the moduli of elasticity. For this reason it is only necessary to carry out the tests in the applicable load range, which thus has to be defi ned. Here it is only possible to provide general data and each individual case is the responsibility of the engineering con-sultancy and the building inspectorate. In general a safety factor of fi ve is used, but this should always be discussed and may deviate in individual

5.6 Cable edge test.

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cases. In this case the working stress is one-fi fth of the strength measured in the single-axis test. The pre-stress is normally about one-fi fth and may be up to one-tenth of the working stress, because it can depend on the curvature of the surface and the web situation. Here the one-fi fth fi gure should be used initially, whereby the pre-stress is about one twenty-fi fth of the single-axis strength. Now it is not always true that the same pre-stress is found in the warp and weft, therefore it is necessary to start with tests in which:

• warp pre-stress : weft pre-stress = 1 : 2 = 1/50 working stress : 1/25 working stress

• warp prestress : weft pre-stress = 1 : 1 = 1/25 working stress : 1/25 working stress

• warp prestress : weft pre-stress = 2 : 1 = 1/25 working stress : 1/50 working stress

are taken as the basis for testing.In addition it is necessary during twin-axis tests to simulate the behaviour

in the building structure, in other words under real conditions. Real loads are snow and wind. If the main anisotropic directions are approximately parallel to the warp and weft, then in this load case one of the directions is loaded and the one which is perpendicular to it is relieved of any load. This procedure is then changed round and the previously loaded direction is unloaded and the previously unloaded direction is then loaded. The direc-tions of the warp and weft depend thereby on the design and the web positions.

It also has to be remembered that the loads for which the stresses are calculated occur only very seldom if at all. For safety reasons the highest load is always used. It is then realistic not to assume that the working stress is the upper limit but that it is only 80% of it. Therefore the upper limit of the load in the test is 0.8 × working stress. A characteristic load history is shown in Fig. 5.7.

Test procedure: According to laboratory specifi cation LBV P 1106

Evaluation: As described belowTest type: See commentsDuty to provide evidence: Coating fi rmTest quantity: At least two of the same pre-stress ratio

Here it is necessary to differentiate between two cases:

• Either the coating company can prove that its product is homogene-ous and this test can be limited to initial approval and external moni-toring or

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• the proof of homogeneity is unsuccessful. It is then necessary to carry out at least one corresponding twin-axis test for each production batch. In the case of larger building projects the tendering engineer can specify self-testing in the tender. The engineer then has the duty of providing evidence which should be discussed individually. This is then incorpo-rated in the price.

Evaluation method for the elastic moduli

We calculate the elastic moduli between an assumed pre-stress of 1 kN/m and an upper value of 10, 20 and 30 kN/m as shown in the load history, Fig. 5.7. The evaluation method is explained in detail in Fig. 5.8 which is extracted from the measured strains of the applied stresses of Fig. 5.7. The procedure corresponds to a typical loading by wind followed by a loading by snow.

Shear behaviour

In Fig. 5.8 the fabric behaviour under parallel thread stresses is described suitably. With the tests defi ned here nothing can be concluded about any possible shear stresses. For this purpose self-testing must be arranged.

Determination of shear modulus

It is possible to determine the shear modulus in two ways:

• In the twin-axis test• In the single-axis test.

The biaxial test is very time-consuming and is only meaningful for the initial approval of a fabric. The sample is shown in Fig. 5.9.

Working tension × 0.8

Stress in warp direction

Stress in weft direction

Pre-tension

Time

0:00

12

10

8

6

4

2

01:12 2:24 3:36 4:48 6:00 7:12 8:24 9:36 10:48

Tensio

n

5.7 Characteristic load history.

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–0.5

0

0.5

1

1.5

2

2.5

Time (hh:mm:ss)

Str

ain

(%

), s

tre

ss

(k

N/d

m) Strain warp

Strain fill

Stress warpStress fill

Δn11Δn22

Δε22

Δε22

Δε11

Δε11

Keder,

detail 1

WarpWarp

α1240

270270

100

1240

700

7 Shackles:

width 100 mm,

length 270 mm

5.8 How to evaluate the elastic moduli.

5.9 Sample shape for the determination of shear behaviour (dimensions in mm).

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It is, however, also possible to set up a one-dimensional alternative test, which is easier to carry out and can be used for monitoring and which is roughly sketched in Fig. 5.10. For evaluation the angular change is mea-sured as a result of the transverse force which was applied.

Relaxation behaviour

Relaxation denotes the decrease in the initially induced stress with constant elongation. Twin-axis relaxation tests are, however, very diffi cult to carry out. Here it therefore makes sense to carry out single-axis tests and then to attempt to calculate the fabric behaviour. As a fi rst approximation it can be assumed that the stress changes linearly with the relaxation behaviour of the thread. The proportionality constants can be calculated from the E-modulus and the relaxation behaviour of the thread.

Creep

The creep behaviour of the fabric can also be traced back in the same way as the relaxation behaviour to the creep behaviour of the thread.

5.10 Proposal for a uniaxial test to estimate shear stiffness.

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5.6 Transmission of light through membranes

A textile membrane changes the light transfer in a building, which affects the visual impression and the energetic input energy of the sunlight. The behaviour of light passing through a material is classifi ed as

• Transmission• Refl exion• Absorption with convection, Fig. 5.11.

These three basic parameters can be signifi cantly different due to the dif-fering wavelengths of sunlight, which is divided into

• Non-visible UV light (100–340 nm wavelength) where– UV-C 100–280 nm– UV-B 280–315 nm– UV-A 315–380 nm

• Visible light (340–780 nm wavelength)• Non-visible infrared light (780 nm to 1000 μm wavelength).

The basic membrane materials differ in the degree of transmission and refl exion (Table 5.1):

• In principle, glass fabrics can transmit more light than polymer fi bre fabrics

• The transmission of light with PTFE coating is higher than with PVC• ETFE fi lms have the highest transmission rate.

The desired values of transmission and refl exion depend on the architec-tural construction:

Light transparency

Transmission of

solar radiation

Total energy

transmission

L

T

G

Ai

Reflexion and

convection inwards

Reflexion and

convection outwards

Reflexion

100% solar

radiation

input

Aa

R

5.11 Solar functions of textiles in construction.

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Table 5.1 Transmission of light

Fabric/coating Type Transmission UV (%)

Transmission visible 340–780 nm (%)

Refl exion visible 340–780 nm (%)

Polyester/PVC Type IType V

00

14 6

Glass fi bres/PTFE Type IType III

0.10.1

1711

7780

Glass fi bres with fl uorfoils

Transmission 43 44

Fabrics for awnings 11–20 50–80PTFE fabrics

uncoated, indoor1–32 19–38 62–81

ETFE fi lms 5–83 40–95

• UV light has to be transmitted if plants have to grow inside.• UV light can be blocked to protect polymers and other materials from

long-term damage by UV.• Visible light transmission of 5% is suffi cient to illuminate a building

during daytime.• For heat management the properties of the light in the infrared (IR)

region are important. Depending on the desired physical functions, transmission or refl exion in the IR region can be highly useful to decrease energy consumption for heating or cooling systems:– For heating an interior room, transmission of short-wavelength IR

and refl exion of long-wave IR radiations is preferred.– Heating can be avoided by refl ecting the UV/VIS/IR radiations.

Special spectrometers can provide information on the transmission, refl ex-ion and absorption behaviour of the various wavelength radiations.

5.7 Heat and energy transport in membranes

5.7.1 Introduction

To point out the energy problems of a membrane envelope, at fi rst a few measurements have to be taken on the membrane structure. In Fig. 5.12 the structure itself, a furniture store, is shown. Figure 5.13 shows the tem-perature profi le in the single layers on a clear winter’s day. The measuring point of the different temperatures was situated on the north side of the building. The material temperatures sank to almost −10°C, even though the air temperature did not sink below 4°C. This effect can only be attributed to radiation. These results were so surprising that it seemed necessary to analyse the energy transmission mechanisms in general.

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28.02.01

14TA

T2

T3

12

10

8

6

4

2

0

–2

–4

–6

–8

–1028.02.01 28.02.01 28.02.01 28.02.01 28.02.01 01.03.01

Time

Tem

pera

ture

(°C

)

PR 515: temperatures over WD, typical daily behaviour

5.12 Outside view of the furniture store near Stuttgart.

5.13 Measured material temperatures at the end of April.

5.7.2 Basic physics of thermal transmission: general comments

During exact analysis three modes of transmission of energy can be distin-guished through closed envelopes:

• Transmission through thermal conduction• Transmission through convection• Transmission through radiation.

These processes will now be discussed in detail.

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Transmission through thermal conduction

The dominating physical laws are the fi rst and second Fick’s Law. This kind of energy transport is relatively slow as the excitation spreads slowly through the continuum.

Thermal transmission through convection

In this case the heat is transmitted through the transport of matter heated up by the environment and through the crossing of this fl ow of matter onto its boundary. The crossing takes place in the thermal interface between boundary and fl ow. This kind of heat transmission mostly takes place in fl uids and gases but also in air. The transport itself is described by the speed of the fl owing medium and by its thermal storage capacity. The thermal transfer is indicated by the thermal exchange constant. The exchange con-stant depends on the tenacity and viscosity of the fl owing medium, on the direction of infl ow in relation to the boundary, and on the roughness of the boundary and its form.

Thermal transfer through radiation

Radiation describes the transport of energy through electromagnetic waves. Electromagnetic radiation does not need any medium. The transport can also happen in a vacuum. The radiation is characterized by wavelength, by amplitude and by swing direction or polarization which is aligned vertically to the expansion of the wave. Every body with a body temperature that is different from absolute zero (0 kelvin = −273°C) radiates electromagnetic waves. The distribution of the wavelength over the total spectrum depends on the surface temperature of the radiating body and its surface condition. The wavelength can also be expressed by radiation temperature or colour.

The radiation from the sun is in general aligned vertically to the surface of the sun. With very good approximation, on earth it can be seen as parallel radiation. Through diffusion and defl ection this parallel radiation is diverted by the geometrical irregularities of the earth’s surface, so that there the so-called diffuse fractions are detectable, whose direction is spread statisti-cally. The diffuse fractions also depend on the season and the geometrical position of the place of impact on the earth’s surface, on the width, and so on.

Radiation interacts with all bodies. This interaction can be indicated through refl ection, transmission and absorption. The refl ection solely depends on the surface condition, meaning the colour and roughness. Naturally, transmission and absorption depend on the thickness of the absorbing layer.

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Solar radiation is not the only effective source of radiation that we have to take into account. According to their surface temperature and their surface condition, all bodies radiate. All in all, the balance of a building element or building depends on the interaction of all radiating surfaces in the environment of the building, including sunlight during the day and the cold universe at night.

Summary of the transport phenomena in the building industry

The above-mentioned mechanisms of thermal transmission and their inter-action towards building elements and their surface are summarized in Figs 5.14–5.17.

Convection

Convection

Thermal wave

Solar radiation

Infrared secondary

radiationReflected solar radiation

Convection

Convection

Solar radiation Infrared secondary

radiation from the outside

Infrared secondary

radiation from the inside

Reflected solar radiation

Penetrated isolation

5.14 Setting of the thermal transport on a massive building element on a clear summer’s day.

5.15 Heating and thermal emission of a membrane.

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Convection

Convection

Thermal wave

Infrared secondary


Infrared primary radiation

from the inside

Convection

Convection

Infrared secondary


Infrared primary radiation

from the inside

5.16 Thermal transport phenomena on a massive building element during a cold and clear winter’s night.

5.17 Thermal transport phenomena at a membrane seal during a cold and clear winter’s night.

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On a clear summer’s day (Fig. 5.14) the outside layer of a massive build-ing element heats up through solar radiation and convection. Thereby a thermal wave is induced which slowly moves towards the inside of the building element. When displaying the thermal conduction characteristics of the material properly, the thermal wave becomes effective on the inside at night when the heating effects such as radiation and convection no longer have an impact. Due to the slow expansion of the thermal wave, neglecting the radiation effects, the slow thermal wave can be described. The spectrum of the impacting radiation is that of the sun.

The setting with a membrane seal is completely different, as shown in Fig. 5.15. Here the outside layer also heats up through solar radiation and convection. The thickness of the membrane is only about 1 mm. Unlike in Fig. 5.14 the membrane is heated up in its total thickness and therefore radiates towards the inside. Thereby the inside is heated up through radia-tion and aside from this through convection. The effect is active immedi-ately, as due to the minor thickness of the membrane the thermal wave immediately heats up the membrane in its total thickness. A buffer action as with a massive building element does not occur. The spectrum of the impacting radiation is again that of the sun. The spectrum of the second-ary radiation is determined by temperature and the material of the membrane.

The setting on a clear winter’s day on a massive building element is pre-sented in Fig. 5.16. Here the outside layer of the building element is cooled due to radiation into the cold winter’s sky and convection. Thereby a thermal wave from the inside towards the outside is activated which in fact has the opposite direction to that in Fig. 5.14, but when displaying the thick-ness of the massive building element and the corresponding choice of mate-rial, due to its low expansion speed, the wave has an impact only when the other conditions have changed again. The energy transport at a membrane seal on a cold clear winter’s night is shown in Fig. 5.17.

As the cold night sky has a low radiation temperature, the membrane radiates towards the sky according to its temperature and its material char-acteristics and immediately cools down due to its minor thickness. Thereby the now warmer inside of the building radiates towards the cooled-off membrane. There is a continuous energy transport from the inside to the outside. The radiation effects are additionally supported by convection.

The main characteristics of the three transport mechanisms are verbally summed up as follows:

• Conduction: Slow, dependent on mass; basis: Fick’s Law, thermal con-duction equation

• Convection: Barrier layer phenomenon of the fl ow; basis: barrier layer theory of the connected fl ow mechanics and thermal conduction of air

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• Radiation: Quanta processes in the electron shells, fast, wavelength dependent; basis: radiation laws.

Accordingly the following can be differentiated:

• Conduction-dominated systems• Convection-dominated systems• Radiation-dominated systems.

This fact can be symbolized in a triangular sketch (Fig. 5.18) showing the three transport mechanisms each in a corner. Classical brick buildings are delineated by the connecting line between convection and conduction. Membrane structures rather are located on the connection line between convection and radiation.

In summary, the energy transmission behaviour of thin textile casings is determined by radiation and convection. Conduction plays a subordinate role, which mostly can be neglected. One can assume that the temperature balance between the air temperature takes place on different sides in the thermal barrier layer and not in one single textile layer. Thus if one wants to understand the energy transmission behaviour of a textile casing one needs to discuss the following radiation mechanisms.

5.7.3 Numerical calculation of radiation

Boltzmann laws

Radiation, to be exact electromagnetic radiation, does not need any medium for energy transport. Transport also occurs in an empty room. Radiation is caused by electron jumps in the electron shells of an atom, through

Convection

Conduction Radiation

5.18 Triangle of transport mechanisms.

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movement of loaded particles in fi elds, through molecular vibrations, etc. Experimentally it was determined that a black body radiates with load I per unit area, which is proportional to the fourth power of the absolute temperature Θ, measured in kelvin:

I = σ Θ 4 5.2

with the Boltzmann constant σ :

σ = 5.67 × 10−8 W K−4 m−2 5.3

So the intensity has the dimensions of load per area. Thereby a black body is defi ned to absorb, meaning to swallow all arriving radiation.

Planck’s law

The distribution of this power density onto the different wavelengths of the radiation is given by Planck’s law:

LC

Cs λ λ

λ

( ) =⎡⎣⎢

⎤⎦⎥

−

−1

5

2 1expΘ

5.4

where

C1 = 3.17 × 10−16 kcal m−6 K−1

C2 = 1.44 × 10−2 m K 5.5

Through recalculation one can easily test, so that the following applies:

CC1

5

2

4

1

λ

λ

λ σ−

⎡⎣⎢

⎤⎦⎥

−=∫

expΘ

Θd 5.6

For structural–physical relevant temperatures, Θ = 253–343 K = −20 to 70°C, the energy curves for black-body radiators are shown in Fig. 5.19. As one can see, the maximum energy values lie in the long-wave infrared area.

The spectral distribution in sunlight is important for structural–physical applications. The surface of the sun has a temperature of about 5000 K. Thus the maximum of the radiated energy lies in the visible area of 200–300 nm. Sunlight is weakened on its way to the earth’s surface through various mechanisms which absorb the energy. For this reason the Planck spectral distribution can be seen as an envelope curve for the radiation arriving on the earth’s surface (Fig. 5.20). The real circumstances are also shown in the fi gure.

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00

2

4

6

8

10

12

14

16323

313

303

293

283

273

263253

18

10 20 30

Wavelength (mm)

Po

wer

per

are

a a

nd

wavele

ng

th (

W/m

2/m

m)

40 50 60

5.19 Energy curves for black-body radiators.

00

2

4

6

8

10

12

14

1 2 43 5

Wavelength (mm)

Po

wer

per

are

a (

W/m

2)

5.20 Envelope for solar radiation arriving on the earth’s surface.

Emissivity and absorption for non-black bodies

Real bodies cannot be accepted as black-body radiators but they have a comparable behaviour which, for example, can be determined for the emissivity:

L L TC

Creal s= ( ) = ( )⎡⎣⎢

⎤⎦⎥

−

−

ε λ ε λ λ

λ

, ,exp

Θ

Θ

15

2 1 5.7

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with emissivity ε, which in general depends on the wavelength and charac-terizes the emissivity of a real body, depending only on the surface. For black-body radiators ε = 1 applies.

The radiated power density again results from integration over all wave-lengths as seen above:

IC

C= ( )

⎡⎣⎢

⎤⎦⎥

−

−

∫ ε λ λ

λ

λ,exp

Θ

Θ

15

2 1d 5.8

Transmission of radiation through an interface with decreasing thickness

As a preliminary to the assembly of a radiation balance when going through an interface of decreasing thickness, the corresponding variables of trans-mission, absorption and refl ection need to be defi ned and their connections discussed. A thin interface is described in the interaction with radiation by the three variables of transmission, absorption and refl ection. As different refl ection capacities are possible on the two sides of the interface, the vari-ables need to be described according to the direction at which the radiation meets the surface. The characteristics of the interface for radiation which approaches from the positive side differ from those for radiation coming from the negative side. Here we denote the variables corresponding to refl ection, transmission and absorption for radiation approaching from the positive side by ρ+, τ+ and α +, and those for radiation approaching from the negative side by ρ−, τ− and α −. As no energy was lost, the following has to apply:

ρ+ + τ+ + α+ = 1

ρ− + τ− + α− = 1 5.9

Thereby the transmission from the positive side is distinguished from the transmission from the negative side. The following thought experiment can be carried out: a beam is followed which approaches the interface from the positive side, passes through the interface and is refl ected on the other side by a perfect mirror. The energy balance of this beam path is

ρ+ + α+ + τ+ (τ− + α− + ρ−) = 1 5.10

which can be transformed into

τ+τ− = τ+ − (1 − τ−)τ− 5.11

For the inverse beam path with a perfect mirror on the positive side, accordingly:

τ+τ− = τ− − (1 − τ+)τ+ 5.12

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Through subtraction of both equations the quadratic equation for τ+ as function of τ− is:

τ+2 + 2τ+ − 2τ−(1 + τ−) = 0 5.13

with the solution

τ+ = −1 ± (1 + τ−) 5.14

The solution with a negative algebraic sign before the bracket is physically not sensible and for the positive algebraic sign before the bracket the fol-lowing applies:

τ+ = τ− = τ 5.15

Both transmission coeffi cients have to be the same but the corresponding refl ection fractions and absorption fractions can be different. For this with the energy balances the following applies:

ρ+ − ρ− = α− − α+ = ε− − ε+ 5.16

Radiation balance of a parallel two-layer system under the infl uence of the radiation of the atmosphere

Here we consider the above-prepared radiation balance of a biplane system made from thin foils. Both planes (numbered 1 and 2) are lined up parallel to each other. The upper plane (2) on the upper side has refl ectivity ρ2+, emissivity ε2+ and absorption α2+, and on the bottom refl ectivity ρ2−, emis-sivity ε2− and absorption α2−; the transmissivity is τ2. Analogous to this, the corresponding variables of the lower plane (1) are given by ρ1+, ρ1−, ε1+, ε1−, α1+, α1− and τ1, where the subscript 1+ describes the characteristics of the upper layer and 1− those of the bottom of plane 1. The temperature of the upper foil is Θ2 and the temperature of the bottom foil is Θ1. In the space above the second upper foil there is a diffuse black-body radiation of tem-perature Θ+∞ and in the space below the fi rst foil a black-body radiation of temperature Θ−∞.

The radiative equilibrium of this system needs to be set up. Only diffuse radiation that fractions are considered in accordance with the optical parameters for diffuse radiation that are to be used. The problem is rela-tively complex and confusing. The single steps for the derivation of the transport equations cannot be discussed explicitly. They are only explained in the corresponding diagrams (Figs 5.21 and 5.22).

Figure 5.21 shows radiation intensities for the passage of an approaching radiation of +00 (here from above) through a two-layer system. The sur-faces of both layers can have different optical characteristics whose nomen-clature is shown in the fi gure. The radiation approaching from above is at

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q (+∞ +∞)

q (+∞ –∞)

–∞

+∞

+2

+1

...

...

...

...

–1

–2

2 Temperature Θ2

1 Temperature Θ1

L+∞ (Λ,Θ+∞) L+∞ρ2+ L+∞τ22ρ1+

L+∞τ2ρ1+

L+∞τ2

L+∞τ22ρ1+

2ρ2–

L+∞τ2ρ1+2ρ2–

L+∞τ2ρ1+ρ2–

L+∞τ1ρ1+ρ2–τ2L+∞τ1τ2

ε2+,ρ2+,τ2

ε1+,ρ1+,τ1

ε1–,ρ1–,τ1

ε2–,ρ2–,τ2

q (–∞ –∞)

q (–∞ ∞)

...

–∞

+∞

+2

+1

...

...

...

–1

–2

2 Temperature Θ2

1 Temperature Θ1

L –∞ (Λ,Θ–∞) L –∞ρ1– L –∞τ12ρ2– L –∞τ1

2ρ2–2ρ1+

L –∞τ1ρ2–

L –∞τ1

L –∞τ1ρ1+ρ2–2

L –∞τ1ρ2–ρ1+

L –∞τ1τ2ρ1+ρ2–L –∞τ2τ1

ε2+,ρ2+,τ2

ε1+,ρ1+,τ1

ε1–,ρ1–,τ1

ε2–,ρ2–,τ2

5.21 Radiation intensities for the passage of an approaching radiation of +00 through a two-layer system.

5.22 Radiation intensities for the passage of an approaching radiation of −00 through a two-layer system.

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fi rst partially refl ected on the ‘+’surface of the second layer, partially pen-etrates through the second layer and then is partially refl ected on the ‘+’surface of layer 1, but partially also transmitted. The refl ected radiation of the ‘+’surface of layer 1 meets the ‘−’surface of layer 2 and there is par-tially refl ected and partially transmitted to +00. This repeats itself endlessly. The total transmitted energy results from the summation through a geo-metrical chain.

Figure 5.22 shows radiation intensities for the passage through of an approaching radiation of −00 (here from below) through a two-layer system. This fi gure arises through exchanging 1 and 2, and + and −. The above explanation can correspondingly be transcribed.

Besides the equations for the radiation from above and below, it has to be considered that both layers show an intrinsic radiation upwards as well as downwards. These fractions also have to be taken into consideration. Figure 5.23 shows secondary radiation based on layer 2. This layer radiates upwards as well as downwards, correspondingly to its emissivity. The down-wards radiated intensity is again, as seen above, partially refl ected on the ‘+’ surface of the fi rst layer and partially transmitted. This act repeats itself,

q (2 +∞)

q (2 –∞)

...

–∞

+∞

...

...

...

+2

–2

+1

–1

2 Temperature Θ2

1 Temperature Θ1

ε2+,ρ2+,τ2

ε1+,ρ1+,τ1

ε1–,ρ1–,τ1

ε2–,ρ2–,τ2

L2ε2+

L2ε2–

L2ε2–τ1 L2ε2–ρ1+ρ2–τ1

L2ε2–ρ1+

L2ε2–ρ1+ρ2– L2ε2–ρ1+2ρ2–

2

L2ε2–ρ1+2ρ2–

L2ε2–ρ1+τ2 L2ε2–ρ1+2ρ2–τ2

5.23 Secondary radiation based on layer 2.

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as seen above, endlessly. Just as layer 2 radiates, layer 1 radiates corre-spondingly to its temperature. The corresponding diagram (Figure 5.24) arises from Fig. 5.23 through exchanging 1 and 2, and + and −.

Total radiation balance

Using the above expressions, one can derive the following for the entire transported radiation capacity from the outside to the inside:

Δ �q L R

L R

+∞ − ∞( ) = −( ) −[ ]− −( )

+∞ + +

−∞ −

∫to dτ τ τ ρ ρ λ

τ τ τ ρ2 12 1 2 1 2

1 12 2 1 2 −−[ ]+ − −( )[ ]− − −

−

− + −

+ −

∫∫

ρ λ

ε ε τ τ ρ λ

ε ε τ τ ρ

1

1 1 1 12 2 1 2

2 2 2 12 1 2 1

d

dL R

L R ++( )[ ]∫ dλ

5.17

The functions L1 and L2 according to the above-mentioned equations still depend on the material temperatures Θ1and Θ2 of layers 1 and 2. It is also notable that the air temperature does not play a role in this expression,

q (1 +∞)

q (1 –∞)

...

–∞

+∞

...

...

...

+2

–2

+1

–1

2 Temperature Θ2

1 Temperature Θ1

ε2+,ρ2+

ε1+,ρ1+

ε1–,ρ1–

ε2–,ρ2–

L1ε1+τ2

τ2

τ1

L1ε1+ρ2–ρ1+τ2

L1ε1+ρ2–2ρ1+

L1ε1+ρ2–ρ1+

L1ε1+ρ2–

L1ε1+

L1ε1– L1ε1+ρ2–τ1 L1ε1+ρ2–2ρ1+τ1

5.24 Secondary radiation based on layer 1.

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which is not surprising as here only transport through radiation is consid-ered. Furthermore it has to be pointed out that all ‘material constants’ are still functions of the wavelength as mentioned above. Additionally the temperatures Θ+00 and Θ−00 are not at all constant but are functions of time. Therefore it is diffi cult to reduce the problem in general to an equation analogous to the determination of the U-value. The equation for the energy transport through radiation can be transformed into:

Δq L T R L T R

L E

= ( ) −( ) − ( ) −( ) +

+ ( ) −+∞ +∞ −∞ −∞

−

∫ ∫λ λ λ λ

λ

, ,

,

Θ Θ

ΘII I

II

d d

2 2 EE L E EII Id d+ + −( ) − ( ) −( )∫ ∫λ λ λ1 1 1, Θ

5.18

with the abbreviations:

TII = TI = T = τ1τ2R12

RII = ρ2+ + τ22R12ρ1+

RI = ρ1− + τ12R12ρ2−

EI+ = ε1+R12(τ2 − τ1ρ2−)

EI− = ε1−

EII− = ε2−R12(τ1 − τ2ρ1+)

EII+ = ε2+

If it is required to optimize the energy transport for whatever reason, the radiation characteristics of transmission, refl ection, emissivity and absorp-tion of both layers on both sides are available.

Layer temperatures

In defi ning the energy fl ow, only the temperatures Θ1 and Θ2 of layers 1 and 2 are still unknown. Here it can be assumed that due to the minor thickness of the membrane the temperatures of the layers are constant across the entire layer. Compensation processes take place in the adjacent air layers and are treated below. These layer temperatures are calculated from the absorbed radiation energies in the single layers, the energies registered by convection and the particular warmth of the layer per unit area. Here only the radiation fractions are processed. For layer 2, for the total radiation infl ow:

q L R L R

L

2 2 2 1 2 12 1 2 12

2 2 2 2

( ) = +[ ] + [ ]− + −

+∞ + + − −∞ −

+ −

∫ ∫α τ ρ α λ τ α λ

ε ε ε

d d

−− + − + −[ ] +∫ ∫ρ α λ ε α λ1 2 12 1 1 2 12R L Rd d

5.19

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Depending on the algebraic sign, this capacity is for either heating or cooling of layer 2 as a result of radiation. Analogously, one may derive the capacity for layer 1:

q L R L R

L

1 1 1 2 1 12 2 1 12

1 1 1

( ) = +[ ] + [ ]− +[ ]

−∞ − − + +∞ +

− +

∫ ∫α τ ρ α λ τ α λ

ε ε

d d

dλλ ε ρ α λ ε α λ∫ ∫ ∫+ ++ − + − +L R L R1 1 2 1 12 2 2 1 12d d

5.20

If c2 is the thermal capacity and μ2 the mass of layer 2 per area unit, neglect-ing convection one can derive for the temperature Θ2 the equation with the starting temperature Θ20 in the radiative equilibrium:

c2μ2(Θ2 − Θ20) = q(2) 5.21

For layer 1 under the same circumstances the following applies:

c1μ1(Θ1 − Θ10) = q(1) 5.22

These are two nonlinear equations for the determination of the tempera-tures Θ1 and Θ2 with known starting temperatures Θ10 and Θ20 and the known temperatures Θ+00 and Θ−00 as functions of time. Thereby the problem of the transport of energy through radiation in principle is solved. The consideration of convection in this system is simple:

One only has to add the energy transfer through convection to the terms of the single layers. This is not explicitly shown here.

As one can see, the equations are highly nonlinear due to the fourth power of temperature and due to the radiation distribution and are strictly connected. Additionally the temperatures at +00 for day and night are very different. During the day the surface temperature of the sun, more than 5000 K, has to be considered, while during the night the air temperature can decrease to about 220 K. Furthermore during the day the radiation has to be split into a direct fraction with a corresponding angle of incidence and a diffuse fraction which is mainly determined by cloudiness. In addition in a multi-layer system not all areas are horizontal and parallel. The consid-eration of convection presents the next diffi culty. All of this does not make the problem clear. In the end only a numerical treatment of the problem on a fast processor remains.

For this reason, Laboratory Blum in cooperation with the engineering offi ce FemScope in Sigmaringen and Tinnit in Karlsruhe developed the program system ‘Textile Climate’, from which the fi rst results are on hand. The input variables are the geometry of the textile casing, the geographical width, the number of layers used, the inner marginal conditions and the radiation characteristics of the various layers on both sides. Then if the temperature gradients during a day and during a year are available, the total energy balance can be calculated.

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Necessary, therefore, are the radiation characteristics of the casing mate-rials on both sides. With the help of the spectroscopy appliance at ITV Denkendorf, these characteristics can be determined in the range of 100 nm up to 25 μm for direct and diffuse radiation.

In conclusion, Plates I–IV (between pages 168 and 169) show some results of calculations using the program ‘Textile Climate’. A comment can be made on the measurement of the passage of energy. Here one has to measure the radiation distribution over the wavelength at the correspond-ing temperatures, under solar radiation over 5000 K and on a clear night at 220 K. All other marginal conditions lead to results which do not comply with reality. Finally, Figures 5.25 and 5.26 show a few spectra of membrane materials.

–0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14 16 18

Absorption spectrumTransmission spectrum

Reflection spectrum

20

–0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14 16 18 20

Absorption spectrumTransmission spectrum

Reflection spectrum

5.25 Transmission, refl ection and absorption spectra for a PVC-coated polyester fabric versus wavelength (μm).

5.26 Transmission, refl ection and absorption spectra for silicone-coated glass fi bre fabric versus wavelength (μm).

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5.8 Chemical, light and fi re durability of membranes

Customarily used membrane materials show good chemical resistance even in the severe conditions of an industrial environment. Hydrolysis and alkali resistance are decisive for ageing resistance.

5.8.1 Comprehensive environmental simulation

Textile membranes are exposed not only to mechanical stresses but also to various environmental infl uences. The main damaging infl uences are tem-perature, humidity, solar irradiation, noxious industrial gases, ozone, dust, salts and micro-organisms. These infl uences impair the functional proper-ties, performance and life-span of the membranes. DIN EN ISO 4892 standard describes the basics for these tests. It is expected that textile mem-branes should last for decades without their properties and performance being compromised. However, every year many materials break down due to severe environmental infl uences and cause damage worth millions of euros.

Accelerated simulation tests are conducted on a laboratory scale to simu-late damaging infl uences due to the environment and to fi nd the life-span of the membranes. The life-span of textile membranes can be determined by the artifi cial ageing test in combination with the functionality test (per-formance test) and the mechanical behaviour. The ageing of the mem-branes is signifi cantly affected by the type of material, climate conditions, concentration of noxious gases (ozone, nitric oxides), irradiance and expo-sure time. Thus the amount of ageing, loss of mechanical properties and deposition of noxious substances on the fi bre surface and fi bre and polymer degradation are used to determine the overall life-span of the membranes. According to the reference values the accelerated ageing could be con-verted to the real life-span. As an example, Table 5.2 shows increasing sensibility to degradation on a scale from 1 to 4.

Table 5.2 Increasing sensibility to degradation on a scale from 1 to 4

Polymer Thermal degradation Photo-oxidation Ozone

Polyethylene 2 3 1Polypropylene 2 4 1Natural rubber 2 4 4Polyamide 6 2 2 2Polyethylene terephthalate 2 1 1Polytetrafl uoroethylene 0 0 0Polypeptides 2 2 2Polyvinyl chloride 4 3 0Polyvinyl acetate 3 3 0Cellulose 2 2 0

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The environmental simulation is done in a suitable climate chamber with climate cycles according to typical, seasonal cycles (DIN EN ISO 4892). Figure 5.27 shows an experimental set-up for environmental simulation with periodic mechanical stress. The analysis of the ageing of coated fabrics/membranes is done by REM, staining reaction, tension strength, aqueous extraction, electrostatic behaviour, visual examination, gloss and bending rigidity.

5.8.2 Light exposure tests

Light fastness can be determined by the following test norms:

• ‘Hot light fastness’: DIN EN ISO 105-B06: Colour fastness and ageing to artifi cial light at high temperatures: Xenon arc fading lamp test

• ‘Light fastness’: DIN ISO EN 105-B02: Colour fastness to artifi cial light: Xenon arc fading test

• ‘Light fastness with exposure to weathering’: DIN ISO EN 105B04: Colour fastness to artifi cial weathering: Xenon arc fading test

• ‘Daylight fastness’: DIN ISO EN 105-B01: Daylight fastness (this test is not accelerating).

Periodic deformation

Air

UV

Temp.

SampleH2O

SO2

NOx

5.27 Example of an environmental simulation set-up in a climate chamber.

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The evaluation of light fastness is made on a grey-scale for assessing the change of colour (ISO 105-A2) or by colour measurement (ISO 105-A05).

The test set-up consists of an exposure unit with an optical light source, a fi lter and a specimen holder. The main parameters are the exposure rate and the spectral energy distribution in the surrounding conditions. The test is conducted under defi ned exposition conditions and exposure cycles. The exposure parameters can be chosen as per the material appli-cation. Thus different exposure conditions render different evaluation processes.

5.8.3 Wicking tests

A wicking test is used to determine the absorptive velocity of water in fabrics. It is known as the capillary rise test (DIN EN 53924). With respect to time, the capillary rise of absorptive fabrics in the warp and weft direc-tions is measured by dipping them in distilled water. The absorptive veloc-ity depends on the capillary force, which determines the transport of liquid contrary to gravity. For fabric the wicking velocity, the path of liquid dis-tribution and the fi nal wet fi gure can be different in the warp and weft directions.

5.8.4 Fire tests B2, B1, A2, A1

The European Commission published the Euroclasses on 8 February 2000. With them the behaviour of membranes towards fi re can be tested by fol-lowing a new concept compared to the existing procedures in Europe. In the Euroclasses seven main new classes are introduced, which are A1, A2, B, C, D, E and F.

• A1 and A2 represent different degrees of limited combustibility.• For linings, B, C, D and E represent products that may go to fl ashover

in a room and at certain times.• F means that no performance is determined.

Thus there are the seven classes for linings and fl oor covering materials. Additional classes of smoke and any occurrence of burning droplets are also given and are shown in Table 5.3.

In many cases the test methods used come from ISO. These are well known and some of them have been in use in various countries throughout the world for many years. ISO/TC92/SC1 standards are in cooperation with the CEN and are actively involved in the development of European stan-dards. Therefore these standards are named EN ISO to indicate that they are worldwide standards as well as European standards.

��


Table 5.3 Standards for fi re resistance

Class Test method(s) Classifi cation criteria Additional classifi cation

A1 EN ISO 1182(1); and

ΔT ≤ 30°C; andΔm ≤ 50%; andtf = 0 (i.e. no sustained fl aming)

–

EN ISO 1716 PCS ≤ 2.0 MJ.kg−1(1); andPCS ≤ 2.0 MJ.kg−1(2)(2a); andPCS ≤ 1.4 MJ.m−2(3); andPCS ≤ 2.0 MJ.kg−1(4)

–

A2 EN ISO 1182 (1);or

ΔT ≤ 50°C; andΔm ≤ 50%; and tf ≤ 20 s

–

EN ISO 1716;and

PCS ≤ 3.0 MJ.kg−1(1); andPCS ≤ 4.0 MJ.m−2(2); andPCS ≤ 4.0 MJ.m−2(3); andPCS ≤ 3.0 MJ.kg−1(4)

–

EN 13823 (SBI) FIGRA ≤ 120 W.s−1; andLFS < edge of specimen; andTHR600s ≤ 7.5 MJ

Smoke production(5); and fl aming droplets/particles(6)

B EN 13823 (SBI); and

FIGRA ≤ 120 W.s−1; andLFS < edge of specimen; andTHR600s ≤ 7.5 MJ


EN ISO 11925-2(8):Exposure = 30 s

Fs ≤ 150 mm within 60 s

C EN 13823 (SBI); and

FIGRA ≤ 250 W.s−1; andLFS < edge of specimen; andTHR600s ≤ 15 MJ




D EN 13823 (SBI); and

FIGRA ≤ 750 W.s−1 Smoke production(5); and fl aming droplets/particles(6)



E EN ISO 11925-2(8):Exposure = 15 s

Fs ≤ 150 mm within 20 s Flaming droplets/particles(7)

F No performance determined

* The treatment of some families of products, e.g. linear products (pipes, ducts, cables, etc.), is still under review and may necessitate an amendment to this decision.(1) For homogeneous products and substantial components of non-homogeneous products.(2) For any external non-substantial component of non-homogeneous products.(2a) Alternatively, any external non-substantial component having a PCS ≤ 2.0 MJ.m−2, provided that the product satisfi es the following criteria of EN 13823 (SBI): FIGRA ≤ 20 W.s−1; and LFS < edge of specimen; and THR600s ≤ 4.0 MJ; and s1; and d0.(3) For any internal non-substantial component of non-homogeneous products.(4) For the product as a whole.(5) s1 = SMOGRA ≤ 30 m2.s−2 and TSP600s ≤ 50 m2; s2 = SMOGRA ≤ 180 m2.s−2 and TSP600s ≤ 200 m2; s3 = not s1 or s2.(6) d0 = no fl aming droplets/particles in EN13823 (SBI) within 600 s; d1 = no fl aming droplets/particles persisting longer than 10 s in EN13823 (SBI) within 600 s; d2 = not d0 or d1; ignition of the paper in EN ISO 11925-2 results in a d2 classifi cation.(7) Pass = no ignition of the paper (no classifi cation); fail = ignition of the paper (d2 classifi cation).(8) Under conditions of surface fl ame attack and, if appropriate to end-use application of product, edge fl ame attack.

��



• EN ISO 1716 describes the determination of combustion heat for infl am-mable materials. The amount of heat energy is an indication of the heat being emitted in case of fi re.

• EN ISO 1182 is applied for non-burning materials, which are heated up in special ovens between 500°C and 750°C. The evaluation includes loss of mass, the ignition of the material and the increase of the oven tem-perature by constant heat input.

• DIN EN ISO 13823 describes the exposition of the material in a free fl ame. The behaviour of the material towards the free fl ame is recorded, where all the measurements are taken in a smoke pipe above the speci-men. The calculation delivers the volume fl ow rate of heat, the amount of emitted heat and smoke. Special considerations should be given to calibration and variations in accuracy.

• DIN EN ISO 11925-2 is similar to DIN EN ISO 13823 but without numerical evaluation. This standard evaluates the fi re behaviour of con-struction materials by visual analysis if ignition is occurring, the height of the top of the fl ame, the time for burning, and whether the fi lter paper, which is inserted above the specimen, has ignited or not.

Figure 5.28 shows the experimental set-up and working principle of the EN ISO 1182 test for non-combustibility.

Airflow stabilizer

Insulated cylindrical

furnace kept at 750°C

Specimen

Specimen

insertion device

5.28 EN ISO 1182 test for non-combustibility.

��



5.9 Surface cleaning properties of membranes

Membranes still have to make a good impression after a long period of time. To avoid contamination of the surface with dirt over a long period of time, special top-coats are used.

To simulate the cleaning behaviour special tests have been developed. Membrane samples 18 cm × 18 cm and test dust AATCC 123 (5% of material weight) are put in a rotating drum of volume 6 litres (Fig. 5.29). The drum rotates for three minutes along the lengthwise axis to soil the test sample on both sides. The difference in weight of the sample before and after soiling and the soiling affi nity as a percentage of dust carry-on on the material are calculated. The lower the amount of dust sticking to the surface of the coating, the lower the dust affi nity. If there is only a small amount of dust on the surface, the rinsing water could clean the surface much more effectively. The soiled sample is compared to a clean sample using the grey-scale according to DIN EN 20105 A03 for assess-ment. In the following the soiled sample is cleaned with 750 ml of deionized water using the spray test according to DIN EN 24920 (Fig. 5.30). The cleaned sample is compared with a clean sample again using the grey-scale (Fig. 5.31).

As an example, Figures 5.32–5.34 show the soiling and cleaning behaviour of standard materials for textile architecture: PVC-coated PET fabric, PTFE-coated glass fabric and silicone-coated glass fabric. Before and after

5.29 Revolving drum.

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5.30 Spray-tester.

1

1

1/2

1/2

2/3

2/3

2

2

3

3

3/4

3/4

4/5

4/5

3

3

4

4

5

5

5.31 Grey-scale for assessment.

soiling, the samples are weighed and the soiling affi nity (per cent relating to material weight) is calculated. The samples are compared to clean samples after soiling and after cleaning by the spray test. The fi gures show, from left to right, clean sample – soiled sample – cleaned sample with grey-scale assessing grades underneath.

��



(a)

(c)

(b)

5.32 PVC-coated samples: (a) before soiling, (b) after soiling, and (c) after cleaning.

5.10 Overview of commonly used standards

for membranes

Table 5.4 summarizes the basic standards for testing mechanical properties and parameters of membranes.

5.11 Future trends: methods of improving

membrane properties

5.11.1 Improving mechanical and chemical durability

A high bending resistance is already required for making up, handling, transporting and setting up and is indispensable for a long life-span of

��



foldable and temporary constructions. Bending resistance is a property which depends on fi bre and fabric parameters as well as on coating poly-mers and the interaction between them. Glass fi bres are brittle in cross-direction which leads to low bending resistance. As with glass it is favourable to use fi ne fi bre fi laments (more fi bres per yarn diameter) than coarse fi bre fi laments, because the bending resistance of fi ne glass fi bres is much higher. However, this could be at the expense of tensile strength.

The top-coats are responsible for the durability and resistance to water and chemical impacts from the environment. Mainly acrylic and fl uori-nated polymers are used for top-coats on various base coats (PVC, PUR, PTFE, silicone rubber, etc.) to enhance resistance to soiling and ageing. Certain additives for UV protection can be added. Due to its self-cleaning non-adhesive surface the top-coat is often hard and brittle. On PVC coatings the top-coat gives not only protection against environmental infl uences but also a barrier against emission of plasticizer out of the PVC.

(a)

(c)

(b)

5.33 PTFE-coated samples: (a) before soiling, (b) after soiling, and (c) after cleaning.

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5.11.2 Improving mechanical, physical and optical properties

The membrane materials used today have only limited barrier properties. Noise or IR radiation can easily penetrate the material. Multi-layered struc-tures composed of supporting textile fabrics and polymeric coatings com-bined with, e.g., three-dimensional textile structures can improve thermal radiation. Humidity and temperature control are under development.

Thermal insulation

Although polymers show low heat conductivity, the thickness of mem-branes (0.2–1.5 mm) is much too little to give good thermal insulation. Thermal insulation can be achieved by encapsulating air between shell layers or within a textile structure, e.g. by combining nonwoven or foamed materials with membranes. Also, phase change materials that store and release heat can be integrated in the coating. In most cases the increase of thermal insulation is at the expense of translucency. By using,

(a)

(c)

(b)

5.34 Silicone-coated samples: (a) before soiling, (b) after soiling, and (c) after cleaning.

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Tab

le 5

.4 S

tan

dar

ds

for

mem

bra

ne

mat

eria

ls

Tec

hn

ical

ch

arac

teri

stic

sU

nit

EN

sta

nd

ard

ISO

sta

nd

ard

Nat

ion

al s

tan

dar

ds

Alt

ern

ativ

e p

rop

osa

l

Bas

e fa

bri

c/ y

arn

M

ater

ial(1

)

W

eig

ht

g/m

2E

N 2

2286

ISO

228

6-2

W

eave

sty

le(2

)IS

O 9

354

NF

G 0

7155

N

o.

of

yarn

s/cm

(w

arp

/wef

t)IS

O 7

211-

2D

IN 5

3853

NF

EN

104

9-2

Y

arn

(w

arp

, w

eft)

cou

nt(3

) , d

iam

eter

of

fi la

men

tsd

tex,

EN

197

3D

IN 5

3830

nu

mb

er o

f fi

lam

ents

μm

tw

ist(4

) , tu

rns

per

met

re,

sizi

ng

(5)

tpm

ten

sile

str

eng

th,

elo

ng

atio

nN

/tex

, %

EN

IS

O 2

062

EN

IS

O 2

062

thre

ads

fro

m f

abri

c

→

red

uct

ion

by

wea

vin

gLB

V 1

101,

LBV

111

3

th

read

s u

nd

er d

efl e

ctio

nLB

V 1

102

lon

g-t

erm

beh

avio

ur

LBV

120

2

Co

atin

g

Mat

eria

l(6)

W

eig

ht

g/m

2E

N 2

2286

ISO

228

6-2

T

ota

l th

ickn

ess

ISO

228

6-3

T

hic

knes

s (t

op

fab

ric)

(7)

mm

inte

rnal

ly

To

p c

oat

(m

ater

ial,

wei

gh

t)(8

)

Co

ated

fab

ric

W

eig

ht

g/m

2IS

O 2

286-

2

Th

ickn

ess

μmE

N 2

2286

ISO

228

6-3

A

vaila

ble

wid

thm

C

olo

ur

��


Fire

rea

ctio

n

No

nco

mb

ust

ibili

ty o

f su

bst

rate

ISO

394

1N

FP 9

2 50

3; A

ST

M E

−13

6;

DIN

410

2; B

S 7

837

In

term

itte

nt

fl am

e, s

pre

ad

o

f fl

ame

AS

TM

E-1

08

E

xter

nal

fi r

e ex

po

sure

ro

of

test

BS

476

par

t 3

Fi

re p

rop

agat

ion

BS

476

par

t 6

S

pre

ad o

f fl

ame

BS

476

par

t 7

Ph

ysic

al p

rop

erti

es

Infr

ared

em

issi

vity

an

d a

bso

rban

ceA

ST

M C

423

-89

A

cou

stic

in

sula

tio

n,

abso

rpti

on

Li

gh

t tr

ansm

issi

on

NFP

385

11;

AS

TM

D 1

494;

A

ST

M E

-903

S

ola

r tr

ansm

issi

on

refl

ect

ance

AS

TM

E 4

24-7

1;A

SH

RA

E 7

4-73

Ag

ein

g,

du

rab

ility

A

ccel

erat

ed a

gei

ng

NF

EN

12

280-

1/2/

3D

IN E

N I

SO

48

92

Sea

ms

S

trip

tes

t te

nsi

leIS

O 1

421

Oth

ers

H

ydro

stat

ic r

esis

tan

ce

Co

ld c

rack

B

urs

t

Cre

ase

P

un

ctu

rin

g

Gas

per

mea

bili

ty

Hyd

roly

sis

resi

stan

ce

Vo

lati

le o

rgan

ic c

on

ten

t

Cle

anin

g a

bili

ty

Rec

ycla

bili

ty

EN

208

11E

N 1

876-

2IS

O 8

11N

F E

N 1

734

NF

G 3

7116

NF

G 3

7131

NF

G 3

7114

NF

G 3

7122

Qu

alit

y as

sura

nce

ISO

900

2

��


ISO

= I

nte

rnat

ion

al s

tan

dar

ds,

EN

= E

uro

pea

n s

tan

dar

ds,

BS

= B

riti

sh s

tan

dar

ds,

DIN

= G

erm

an s

tan

dar

ds,

NF

= Fr

ench

sta

nd

ard

s,

LBV

= B

lum

Lab

ora

tory

pro

toco

ls.

(1) P

oly

este

r (P

ES

or

PE

T),

hig

h t

enac

ity

po

lyes

ter

(PE

S H

T),

gla

ss (

G);

EC

6 m

ean

s co

nti

nu

ou

s E

-gla

ss m

ult

ifi la

men

t ya

rn o

f 6

μm

dia

met

er f

or

each

fi la

men

t; p

oly

tetr

afl u

oro

eth

ylen

e (P

TFE

).(2

) Wea

ve p

atte

rn:

pla

in w

eave

fab

ric;

2 ×

2 b

aske

t w

eave

(o

r p

anam

a);

2 ×

2 tw

ill w

eave

; 4

× 1

sati

n w

eave

.(3

) Co

un

t: l

inei

c d

ensi

ty,

1 te

x =

1 g

/100

0 m

; 1

dte

x =

1 g

/10,

000

m;

1 d

en =

1 g

/900

0 m

.(4

) Tw

ist

= S

or

Z.

(5) S

izin

g o

r fi

nis

h.

(6) P

oly

vin

yl c

hlo

rid

e (P

VC

), a

cryl

ics

(AC

R),

sili

con

e (S

IL),

po

lyvi

nyl

fl u

ori

de

(PV

F),

po

lyte

trafl

uo

roet

hyl

ene

(PT

FE).

(7) M

easu

rem

ent

of

the

coat

ing

th

ickn

ess

bet

wee

n t

he

top

of

the

bas

e fa

bri

c an

d t

he

top

su

rfac

e o

f th

e co

ated

fab

rics

, b

y u

sin

g

eval

uat

ion

un

der

mic

rosc

op

e o

f cr

oss

-sec

tio

n.

(8) A

cryl

ics

(AC

R),

po

lyvi

nyl

fl u

ori

de

(PV

F),

po

lyvi

nyl

iden

e fl

uo

rid

e (P

VD

F).

So

me

con

vers

ion

fo

rmu

lae:

EE

Nte

xG

Pa

gcm

()=

()

()

ρ3

wh

ere

ρ =

volu

met

ric

wei

gh

t o

r d

ensi

ty

TS

tex

gcm

cm(

)(

)(

)=

××

ρ3

210

5 w

her

e T

= c

ou

nt;

S =

cro

ss-s

ecti

on

al a

rea

DT

μm

dte

x

gcm

()=

()

()

1128

3.

ρ w

her

e D

= d

iam

eter

of

on

e fi

lam

ent

of

cou

nt

T

Tab

le 5

.4 C

on

tin

ued

��



e.g., translucent aerogels integrated in a liner, the membrane structure shows excellent thermal conductive properties, which result from the poros-ity of the aerogel of more than 95%.

Light transmission and refl exion

Additives and special surface modifi cations can modify the interaction of coatings and top-coats with UV, IR and visible radiation. Metal oxides such as titanium dioxide (TiO2) or indium oxide (InO) are well known for their high level of transparency for visible light and high refl exion of UV or near-IR radiation. The best way to use these metal oxides is as nano-sized particles either mixed in the top-coating polymer or deposited on the surface of the coating by plasma technology such as physical vapour deposi-tion (PVD) or atmospheric plasma technology such as dielectric barrier discharge (DBD).

Increasing requirements for light and heat transmission, sound absorp-tion and acoustics are leading to new material designs such as low-e materials.

5.11.3 Improving weight

The usual weight of membranes lies between 200 and 1500 g/m2. Such membranes are favourable for designing large span lengths. These materials have to be strong enough to carry their own weight as well as the loads coming from the environment such as wind, rain, snow and ice. If in future new fi bre materials are available with high modulus, the weight of the membrane material can be reduced.


R. Blum: Beitrag zur nichtlinearen Schalentheorie in covarianter Schreibweise mit Anwendung auf die Schalentheorie, Dissertation, Stuttgart, 1970

R. Blum: Die Schale, interpretiert als multipolares Kontinuum, ZAMM 51, 1971

R. Blum, M. Losch and E. Luz: Ein nichtlineares zweidimensionales Stoffgesetz für eine anisotrope hyperelastische Membran unter endli-chen Verzerrungen, in: Beiträge zur Mechanik, Festschrift zum siebzigsten Geburtstag von Herrn Prof. Dr. phil. Dr.-Ing. E. h. Udo Wegner, Stuttgart, 1972

R. Blum: Ein Beitrag zur Schalentheorie, in: Beiträge zur Mechanik, Festschrift zum siebzigsten Geburtstag von Herrn Prof. Dr. phil. Dr.-Ing. E. h. Udo Wegner, Stuttgart, 1972

��



R. Blum, M. Losch and E. Luz: Bestimmung der elastischen Stoffkenngröß en einer Gewebefolie, Materialprüfung 15, 1973

R. Blum, M. Losch and E. Luz: Ein nichtlineares zweidimensionales Stoff-gesetz für eine hyperelastische Membran unter endlichen Verzerrungen, ZAMM 54, 1974

R. Blum: Bestimmung der Eulerschen Spannungen in vorgespannten Membranen durch Messung von Wellenlaufzeiten, in: Arbeitsunterlagen zum Internationalen Symposion Weitgespannte Flächentragwerke, Stuttgart, 1976

R. Blum: Zur Wellenausbreitung in vorgespannten Membranen, in: Vor-berichte zum 2. Internationalen Symposium Weitgespannte Flächentrag-werke, Stuttgart, 1979

R. Blum: Mechanics of fabrics in tension structures, in: Mechanics of Flexible Fibre Assemblies, ed. J.W.S. Hearle, J.J. Thwaites and J. Amirbayat, Sijthoff & Noordhoff, Alphen aan den Rijn, 1980

R. Blum: Tensile membrane structures, in: Air Supported Structures: The State of the Art, The Institution of Structural Engineers Symposium, London, 1980

R. Blum: Spannungsmessungen in vorgespannten Membranen, in: Mem-brankonstruktionen 2, E. Bubner Herausgeber, Köln, 1980

R. Blum: Spannungsmessungen in vorgespannten Membranen, in: Lufthal-lenhandbuch, Mitteilungen des Instituts für Leichte Flächentragwerke, IL 15, Stuttgart, 1984

R. Blum: Über den Einfl uss der tangentialen Steifi gkeiten und der Krümmung auf das Tragverhalten von vorgespannten Membranen, in: Werkstoff und Konstruktion, Festschrift zum 60. Geburtstag von Herrn Professor Dr.-Ing. Gallus Rehm, Stuttgart, 1984

R. Blum and W. Bidmon: Jahresbericht 1982/1983 des SFB 64, Gruppe K4, in: Mitteilungen des SFB 64 Weitgespannte Flächentragwerke, Heft 69, 1984

R. Blum and K. Kerkhof: Analyse von Bauschäden durch Schwingungsmes-sungen unter mikroseismischer Erregung, in: Werkstoff und Konstruktion, Festschrift zum 60. Geburtstag von Herrn Professor Dr.-Ing. Gallus Rehm, Stuttgart, 1984

G. Rehm and R. Blum: Der Entwurfsprozess eines Membranbauwerks und die relevanten Materialkennwerte, in: Berichtsheft 2 zum 3. Internationalen Symposium Weitgespannte Flächentragwerke, Stuttgart, 1985

R. Blum: Das Spannungs-Dehnungs-Verhalten von beschichteten Geweben und sein Einfl uss auf das Tragverhalten von gekrümmten Membranen, in: Berichtsheft 2 zum 3. Internationalen Symposium Weitgespannte Flächentragwerke, Stuttgart, 1985

��



R. Blum, K. Kerkhof and E. Luz: Analyse von Bauschäden unter mikro-seismischer Erregung, Vortrag gehalten auf dem ZfPBau-Symposium, 2–3 October 1985, Berlin

G. Rehm, E. Luz, R. Blum and K. Kerkhof: Überwachung von Bauwerken durch Schwingungsmessungen unter mikroseismicher Erregung, Bericht des Institutes für Werkstoffe im Bauwesen der Universität Stuttgart, 1985

R. Blum and W. Fobo: Über die Mechanik des Druckholzes, arcus 4, 1985R. Blum: Beitrag zur nichtlinearen Membrantheorie Habilitationsschrift,

veröffentlicht als Mitteilung des SFB 64, Weitgespannte Flächentragwerke, Heft 73, 1985

R. Blum and W. Bidmon: Spannungs-Dehnungs-Verhalten von Bautextilien, Theorie und Experiment, Sonderforschungsbereich 64, Universität Stuttgart, Institut Weitgespannte Flächentragwerke, Mitteilungen 74, 1987

R. Blum: Zeltbaumaterialien, in: Leicht und Weit, Zur Konstruktion weitges-pannter Flächentragwerke, Weinheim, 1990

R. Blum: Material properties of coated fabrics, in: Tensinet-Symposium: Designing Tensile Architecture, Brussels, 2000

R. Blum and H. Bögner: A new class of biaxial machine, Tensinews Newsletter 1, Web Publication, 2001

R. Blum and H. Bögner: Evaluation methods for elastic moduli, Tensinews Newsletter 3, Web Publication, 2002

R. Blum: Design process of a membrane structure and the relevant material properties, in: Tensinet-Symposium: Designing Tensile Architecture, Brussels, 2003

R. Blum: Acoustics and heat transfer in textile architecture, Vortrag Techtextil 2003, Frankfurt

R. Blum, H. Bögner and G. Némoz: Materials properties and testing, in: European Design Guide for Tensile Surface Structures, Brussels, 2004

R. Blum, H. Bögner and G. Némoz: Testing methods and standards, in: European Design Guide for Tensile Surface Structures, Brussels, 2004

R. Blum, H. Bögner, K. Gipperich and Sean Seery: An example of the application of the testing procedure described on a PTFE-coated glass fabric, in: European Design Guide for Tensile Surface Structures, Brussels, 2004

J. Chilton, R. Blum, T. Devoulder and P. Rutherford: Internal environment, in: European Design Guide for Tensile Surface Structures, Brussels, 2004

H. Bögner: Vorgespannte Konstruktionen aus beschichteten Geweben und die Rolle des Schubverhaltens bei der Bildung von zweifach gekrümmten Flächen aus ebenen Streifen, Dissertation, Institut für Werkstoffe im Bauwesen der Universität Stuttgart, 2004

��



R. Blum and H. Bögner: On the importance of elastic moduli in the analysis of membrane structures, Lecture of the ECCOMAS-Symposium: Textile Composites and Infl atable Structures II, Stuttgart, October 2005

H. Bögner and R. Blum: The mechanical behaviour of coated fabrics used in prestressing textile engineering: Theory, simulation and numerical analysis to be used in a FEM-model, Lecture of the ECCOMAS-Symposium: Textile Composites and Infl atable Structures II, Stuttgart, October 2005

R. Blum and H. Bögner: The mechanical behaviour of coated fabrics and fi lms used in prestressed textile engineering: Its importance in the analy-sis and how to derive a membrane stiffness by simple theoretic consid-erations, Tensinews Newsletter 10, April 2006

R. Blum, editor, with contributions from R. Blum, H. Bögner, J. Köhnlein and K. Reimann: Handbook of Prestressed Structures: Architecture, Acoustics, Energy, Design Process, Differential Geometry, Membrane Theory, Theory of Cable Nets, Analysis, Numerics, Material Behaviour, Structural Design, Testing, Manufacturing, Erection. In preparation, will appear in September 2010

Robert Siegel and John Howell: Thermal Radiation Heat Transfer, Taylor & Francis, New York and London, 2002

R. Blum: Handbuch des Textilen Bauens, Erscheint Herbst, Stuttgart, 2009H. Bögner and R. Blum: Crack propagation and damage, in Tensinet

Symposium, Milan, 2007P. Schneider, T. Stegmaier, M. Linke, M. Schweins and H. Planck: Con-

struction with technical textiles – Chance and challenge, CD from the 46th Man-Made Fibres Congress, Dornbirn, Austria, 17–19 September 2008

T. Stegmaier and H. Planck: New material developments with textiles, Paper at the International Conference on Textile Composites and Infl atable Structures, Structural Membranes 2007, Barcelona, Spain, 17–19 September 2007

5.13 Bibliography

Houtman, R., Orpana, M.: Materials for membrane structures, Bauen mit Textilien, issue 4, 2000

Koch, K.-M. (ed.): Bauen mit Membranen, der innovative Werkstoff in der Architektur, Prestel-Verlag, München, 2004

Schneider, P., Stegmaier, T.: Textile Membranen für die Anwendung im Bauwesen, Ingenieur-Nachrichten, issue 6, 2006

Stegmaier, T.; Linke, M.; Sarsour, J.; Schneider, P.; Schweins, M.; Planck, H.: Heat and light management of textile materials for construction, Lecture at ARCHITEX 2008, Turin, Italy, 1–2 July 2008

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Temperature (°C)293.00 302.30 311.59 320.69 330.18 339.48

Temperature (°C)

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Plate III Temperature distribution in an industrial building with a double-layered cushion roof under solar radiation in a clear sky. Here a solid layer in the air is noticeable (calculated using ‘Textile Climate’, Laboratory Blum, FemScope).

Plate IV Temperature distribution in an industrial building with a double-layered cushion roof under a clear sky at night. A solid layer is hardly visible and unstable air currents appear. The material tempera-tures drop to −10°C (calculated using ‘Textile Climate’, Laboratory Blum, FemScope).

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189

6Polymer foils used in construction

L. SCHIEMANN, Mayr | Ludescher | Partner, Germany and K. MORITZ, seele cover GmbH, Germany

Abstract: This chapter fi rst introduces the construction forms and variants of ETFE-foil structures and offers an overview of the development of ETFE-foil constructions within the fi eld of architecture. Subsequently, the morphological structure of ETFE and the manufacturing process as well as the material behaviour and load-bearing characteristics of ETFE-foils are outlined. The fi nal section discusses future development potentialities and future applicability of ETFE-foil construction methods in structural engineering.

Key words: ETFE, membrane, viscoelastic, cushion, polymer.

6.1 Introduction

For over two decades, transparent foils made out of the fl uorine-polymer material ETFE (ethylene-tetra-fl uorine-ethylene) have been increasingly used for roof structures and facade constructions. As a result ETFE-foils are in direct competition with other materials such as glass, fi bre-reinforced plastics or textile membranes. Frequently the advantageous physical quali-ties of ETFE foils are decisive for their use. These advantages can be opti-mally utilised in the construction of sports venues, greenhouses, zoological facilities or swimming and leisure pools.

With the use of ETFE-foils in the building envelope of impressive large-scale projects such as the Allianz Arena in Munich built in 2005, or the Olympic stadium and swimming pool in Beijing built for the Olympic Games in 2008, the material and construction method have once more been moved into the spotlight of the public’s architectural interest.

ETFE-foils as a fl uorine-polymer material differ fundamentally from textile membrane materials in terms of their thermal–mechanical as well as building–physics behaviour. This chapter fi rst introduces the construction forms and variants of ETFE-foil structures and provides an overview of the development of ETFE-foil constructions from an architectural perspective. Subsequently, the morphological structure of ETFE and the manufacturing process as well as the material behaviour and load-bearing characteristics of ETFE-foils are outlined. The fi nal section discusses future development potentials and the future use of ETFE-foil constructions in structural engineering.

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6.2 Construction methods and types of ETFE-foil

structures

In accordance with Figs 6.1 and 6.2, two principal construction methods can be distinguished for ETFE-foil constructions, differentiated by the type of pre-stressing (mechanical or pneumatic pre-stressing), as well as the type of predominant surface curvature (synclastic or anticlastic Gaussian curvature).

6.2.1 Mechanically pre-stressed systems

The stabilisation of one-layer ETFE-foil constructions takes place by mechanical pre-stressing. The shortened foil has to be mechanically stretched in order to be mounted on the boundary. In the pre-stressing state, these foil geometries display anticlastic curved surfaces, i.e. surfaces curved in the opposite direction in both principal stress directions. The Gaussian curva-ture as the product of both main curvatures κ1 and κ2 of the foil geometry is less than zero.

6.1 Pneumatically pre-stressed ETFE-foil cushion with predominantly synclastic curvature.

6.2 Mechanically pre-stressed single-layer ETFE-foil structure with anticlastic curvature.

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Polymer foils used in construction 191


6.2.2 Pneumatically pre-stressed systems

The foil layers of pneumatic ETFE-foil cushions are pre-stressed by inter-nal pressure, which can be formed as either positive or negative pressure. Those multi-layered ETFE-foil cushions form predominantly synclastically curved surfaces, i.e. surfaces curved in the same direction in both main stress-axes. The Gaussian curvature is greater than zero for all surface points within the area of the synclastic curvature.

In contrast to textile membrane constructions, e.g. PVC-coated polyester fabric or PTFE-coated fi breglass fabric, pneumatic ETFE-foil cushions display small anticlastic curvatures in the bordered corner regions. This is caused by the greater shear stiffness of the ETFE-foils in comparison to the textile membrane materials. Figure 6.3 shows the distribution of anti-clastic and synclastic curvature areas on a square cushion. Figure 6.4 illus-trates the corner region with the counter-curvature.

Anticlastic

area

Synclastic

area

6.3 Synclastic and anticlastic areas of a square ETFE-foil cushion.

6.4 Corner region of a square ETFE-foil cushion with anticlastic curvature.

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6.2.3 Construction types

Corresponding to the number of foil layers and the construction of the middle layer, six principal construction variants can be distinguished for pneumatic ETFE-foil cushions. Due to the diffi culties in welding, cushions made from ETFE generally feature three foil layers at most. The individual construction variants of the foil cushions differ in terms of load-bearing and building-physics characteristics. The middle foil layer for the most part serves as a dual-chamber system with improved heat insulation. By separat-ing the individual foil layers at the anchoring profi les (Fig. 6.5: positions 5 and 6) the protection against loss of heat is further improved, because the individual layers at the anchoring profi le are no longer joined into a single line. If the incline of the foil cushion is suffi cient, the planar pre-stressed middle layer in a dual-chamber system could serve as a water-dispersing layer.

Sun protection elements (aluminium and ETFE lamellae, or mobile textile membranes, cf. Fig. 6.6) can be integrated for further building-physics improvement in the clearance of dual-chamber systems with separate layers. In variants with a curved middle layer and decoupled volumes, and different pressures, the middle layer can assume the sun protection role. For this, the outer and middle foil layers display a print of inversely arranged patterns. The translucency of the cushions is controlled by adjusting the middle layer through pressure control of the two air-chambers.

1. Single-layer single-chamber cushion

with rigid base

2. Two-layer single-chamber cushion

3. Two-layer dual-chamber cushion,

planar middle layer

4. Three-layer dual-chamber cushion,

curved middle layer


planar middle layer and separate

layers


curved middle layer and separate

layers

6.5 Construction types of pneumatic ETFE-foil cushions.

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6.3 Historical development: signifi cant

ETFE projects

The fi rst signifi cant utilisations of ETFE-foils for building envelopes in structural engineering occurred at the beginning of the 1980s. In compari-son to conventional building materials like steel, reinforced concrete, wood, brick, glass, or textile membrane materials, the construction method with ETFE-foils is relatively young. The following signifi cant ETFE-foil projects, which have infl uenced the development of ETFE-foil constructions in a trend-setting way, are illustrations of the historical development of the last nearly 30 years.

6.3.1 1982 Mangrove Hall, ‘Burgers’ Zoo’, Arnhem

The Mangrove Hall in the ‘Burgers’ Zoo’ of Arnhem (Holland), built in 1982, is considered one of the fi rst permanent and large-scale pneumatic ETFE-foil roofs. The cable-supported ETFE-foil cushions have a span of about 3.0 m. In the period that followed until the end of the 1980s, the further utilisation of EFTE-foils in structural engineering was reduced to a rather subordinate application, e.g. in greenhouses, warehouses, or protective covers (against the weather) of solar panels and parabolic mirrors. With the 1990s, a signifi cantly intensifi ed utilisation of ETFE-foils in structural engineering began. ETFE-foils used as building envelopes for facades and roof structures were now specifi cally used functionally, but also architecturally. In combination with steel cables in the form of individual cables or cable nets for the enhancement of load-bearing capac-ity of the ETFE membranes, the spans of foil structures were continuously increased.

6.6 Integrated sun protection elements of ETFE foil cushions with (a) aluminium lamellae and (b) textile membrane (photos: L. Schiemann).

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6.3.2 1994 Lion House, Hellabrunn Zoo, Munich

Of signifi cance in this context is the Lion House in the Hellabrunn Zoo in Munich, Germany, dating from 1994 (Fig. 6.7). In this project for the fi rst time 64 pneumatic ETFE-foil cushions were mounted on an anticlastically curved cable net. The pre-stressed stainless steel net, consisting of meridian and ring cables, is fi xed to two pylons, both about 17 metres high, as well as eight columns with anchoring cables positioned in a circle around the outside. The 64 ETFE-foil cushions run from the ridge to the eaves and have a maximum width of approximately 2.0 m and a maximum length of approximately 20 m.

6.3.3 1996 Moveable ETFE-foil cushion, Olympic Park, Munich

The moveable ETFE-foil cushion in the Olympic Park of Munich, built in 1996 (Fig. 6.8), is one of the fi rst mobile elevating roofs in the form of a pneumatic ETFE-foil roof. The two-layered ETFE-foil cushion serves as roofi ng for the facilities of the Olympiapark GmbH. It has a diameter of about 23 metres. The outer membrane layer consists of PTFE laminated airtight fi breglass mesh; the lower membrane layer consists of ETFE-foils,

6.7 Lion House, Hellabrunn Zoo, Munich (photos: L. Schiemann).

6.8 Moveable ETFE-foil cushion, Olympia Park, Munich (photo: K. Moritz).

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supported by a cable net. Eight telescope-like steel tube pillars with inte-rior-threaded spindles enable the air-infl ated roof structure to be lifted by about 1.0 m in order to ventilate the interior courtyard.

6.3.4 1996 Airtecture, Esslingen

One of the fi rst air-infl ated structures made from ETFE-foils among other materials that is stabilised by negative pressure is the temporary hall, called ‘Airtecture’, of the company Festo in Esslingen, Germany, built in 1996.

6.3.5 1999 Thermal Baths, Prien, Lake Chiemsee

The single-layered ETFE-foil canopy of the Thermal Baths in Prien at Lake Chiemsee, Germany, from 1999 (Fig. 6.9) is one of the fi rst permanent mechanically pre-stressed ETFE-foil roofs. The basic structure of the canopy consists of 18 gluelam girders, cantilevering by about 4.0 m, at a distance of 5.0 m from each other. In between, one single-layer ETFE-foil membrane each is spanned, which is supported by three steel cables each at a distance of 1.25 m per cantilevering roof panel. The complete single-layer roof area amounts to 200 m2. Each roof panel between the gluelam girders covers an area of about 12 m2. Anchoring profi les on the gluelam girders anchor the foil to the primary structure. The frontal free roof edge of the foil roof is formed by garland cables.

6.3.6 2000 Cycle Bowl, Expo Hanover

With the exhibition hall of Duales-System-Deutschland GmbH for Expo 2000 in Hanover, Germany (Fig. 6.10), for the fi rst time for a three-layered

6.9 Thermal Baths, Prien at Lake Chiemsee (photos: L. Schiemann).

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air-infl ated cushion the light transmission of the outer foil membrane could be controlled by regulation of two different internal chamber pressures. The outer and middle layers of the ETFE-foil cushions were printed with alter-nating patterns. By controlling the internal pressure in both chambers, the middle tailored foil layer can be joined to the outer foil layer. The two alternating print patterns thereby complement each other to form a nearly opaque cover.

6.3.7 2001 Garden of Eden, St Austell, Cornwall

The building envelope of the ‘Eden Project’ in St Austell, Cornwall, England (Fig. 6.11), spans an area of about 30,000 m2 and thus constitutes the largest exhibition greenhouse in the world (LeCuyer, 2008). The geodesic steel

6.10 Cycle Bowl, Expo Hanover (photos: K. Moritz).

6.11 Garden of Eden, St Austell, Cornwall (photo: S. Robanus).

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domes with radii ranging from 18 to 65 m form hexagons with diameters between 5 and 11 m, which are spanned by cable-supported ETFE-foil cushions. Because of its dimensions and its architectural aesthetic, the Eden Project upstaged all ETFE-foil constructions built until then.

6.3.8 2001 Information Centre, Walchensee Power Station, Kochel am See

Based on the experience with the single-layer foil canopy of the Thermal Baths in Prien (see Fig. 6.9), a single-layer ETFE-foil roof was built for the entrance area of the information centre of the Walchensee Power Station in 2001 (Fig. 6.12). Aluminium tubes serve as substructure of the almost planar, mechanically pre-stressed foil membrane. These tubes run at a dis-tance of 1.25 m and are fi xed on arched gluelam girders. The foil membranes are attached to the aluminium tubes via welded foil strips on the ETFE foils. The ETFE roof assembled into one piece has a total area of about 400 m2.

6.3.9 2002 Masoala Rainforest, Zurich Zoo

The Masoala Rainforest Hall in the Zurich Zoo, Switzerland (Fig. 6.13), displays the fl ora and fauna of the Masoala peninsula on Madagascar. Between the arched Vierendeel trusses made from steel, three-layered

6.12 Information Center, Walchensee Power Station, Kochel am See (photo: K. Moritz).

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ETFE-foil cushions are spanned. For the fi rst time a fourth ETFE-foil layer was additionally used as a protective and abrasion layer against hailstorms. The maximum span of the verge cushion measures 3.90 m with a maximum length of 106 m. With the Masoala Rainforest Hall three-chamber air-infl ated structures were used in this dimension for the fi rst time.

6.3.10 2002 Conference Building, Deutsche Bundesstiftung für Umwelt, Osnabrück

The outer roof cladding of the conference building of the Deutsche Bundesstiftung für Umwelt in Osnabrück, Germany (Fig. 6.14), is formed

6.13 Masoala Rainforest, Zürich Zoo (photo: K. Moritz).

6.14 Conference Building of Deutsche Bundesstiftung für Umwelt, Osnabrück (photo: R. Barthel).��



by a mechanically pre-stressed single-layer ETFE-foil, which spans between arched gluelam girders with a span of about 1.40 m. The foil membrane with a thickness of 225 μm serves as outer cladding of the roof with air insulation and functions for the fi rst time as a part of the building-physics concept. In addition to the adjustable lamellae above the conference room, the single-layer foil is also an element of the lighting concept of the building.

6.3.11 2004 ETFE-foil umbrellas, Industrie- und Handelskammer, Würzburg

With the three umbrellas in the courtyard of Industrie- und Handelskammer in Würzburg, Germany, for the fi rst time single-layer ETFE-foils in combi-nation with a cable net (8 and 10 mm in diameter) were used for a double curved membrane with a low point. The edge lengths of the umbrellas, which are square in the layout, measure 6.5, 11 and 14 m. The cable net is formed by meridian cables in ETFE-foil pockets and ring cables, which are positioned freely under the foil.

6.3.12 2005 Allianz Arena, Munich

The 2760 rhombic ETFE-foil cushions form the stadium envelope of the Allianz Arena in Munich, Germany (Fig. 6.15), measuring 74,000 m2. The two-layered ETFE-foil cushions exhibit a maximum dimension between axes of approximately 4.5 by 16.5 m. The innovative form, structure and light-ing of the stadium envelope irrevocably established ETFE-foils as an archi-tecturally and constructively interesting material in structural engineering.

6.3.13 2005 AWD-Arena, Hanover

The Niedersachsenstadion in Hanover was remodelled for the Soccer World Championship 2006 in Germany. The stadium roof of the renamed AWD-Arena (Fig. 6.16) is for functional and architectural reasons divided into an outer, opaque roof made of profi le sheeting (16,000 m2) and an inner, transparent ETFE-foil roof (10,000 m2). The inner ETFE-foil roof consists of 34 nearly rectangular roof elements. The maximum dimension of one roof element is about 360 m2. The primary structure of each ETFE-foil roof element consists of two lateral unbraced beams, six cross-trusses and 9–13 steel cables to support the ETFE-foils (foil thickness 250 μm). On the cross-trusses cable clamps are fi xed. The maximum span between the cables is approximately 1.45 m and the span of the transparent roof is about 23.5 m. The transparent ETFE-foil roof of the AWD-Arena was until then the biggest one-layer ETFE-foil structure. The fi ligree steel structure in

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6.15 Allianz Arena, Munich (photo: L. Schiemann).

6.16 AWD-Arena, Hanover (photos: K. Moritz, C. Voigtmann).

combination with the ETFE-foil roof construction was awarded the German Steel Construction Prize in 2006.

6.3.14 2005 Atrium Roof IABG, Ottobrunn

The atrium roof of the IABG Corporation in Ottobrunn, Germany (Fig. 6.17), consists of three-layered ETFE-foil cushions with a total area of 1850 m2. Rectangular, three-layered ETFE-foil cushions span between

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approximately 38 m long trussed girders of steel. The maximum span of the cushions is about 5.40 m. With this project, a dual-chamber system with different air pressures and a curved middle layer was used for the fi rst time in order to make the large spans of the rectangular cushions possible. Thus, the middle layer was considered in the load transfer of the high wind loads. The lower foil layers are additionally supported by steel cables at a distance of 1.5 m from each other.

6.3.15 2005 Tropical Island, Brand

In the course of remodelling the CargoLifter dockyard hall into the ‘Tropical Island’ water park in Brand, Germany, the multi-layered fabric membranes (PVC-coated PES-fabric) in four of the arch planes were replaced with three-layered ETFE-foil cushions. The total area of the transparent foil cushions measures 20,000 m2. Each ETFE-arch plane is formed by 14 foil cushions. The cushions at about 400 m2 were the largest ETFE-foil cushions built until then. For the fi rst time an inner and an outer steel cable net were used to support the foil layers against wind and snow loads.

6.3.16 2008 National Swimming Centre and Olympic Stadium, Beijing

The almost fully square indoor swimming pool of the Summer Olympic Games 2008 in Beijing, China (Fig. 6.18), features a clear span of about 177 m. The primary support structure consists of a hexagonal irregular grid support structure, arranged in two layers. By mounting a total of 3500 ETFE-foil cushions to the outer and inner layers of the primary grid struc-ture, the building envelope constitutes a double facade, which effectively improves the heat insulation. The facade area is formed of two three-layered foil cushions each; the roof area is formed of two four-layered ETFE-foil cushions each.

6.17 Atrium roof, IABG Ottobrunn (photos: L. Schiemann).

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The swimming stadium in Beijing, the so-called ‘Water Cube’, is distin-guished architecturally by its depiction of water as water spume in the form of soap bubbles, with the help of the curved air-infl ated ETFE-foil elements. The ETFE-foil cushions in combination with the bodies of water, which are arranged around the swimming stadium, are designed to suggest sustain-ability and economical energy consumption of the built-up surroundings in the form of naturally temperature-controlled, energy-saving spaces (LeCuyer, 2008).

In the immediate vicinity, the Olympic Stadium (Fig. 6.19) was newly constructed for the Olympic Games 2008. The envelope of the stadium between the very massive steel beams is formed – with reference to the system of the AWD-Arena in Hanover (see Fig. 6.16) – by a single-layer ETFE-foil membrane with cable support. The two Olympic buildings, the Swimming Stadium and the Olympic Stadium, led to further establishment of foil construction in Asia.

6.18 National Swimming Center, Beijing (photo: V. Dangl).

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6.4 Typology, basic shapes and range of application

The above descriptions of the various projects show that there are no limita-tions in principle to the great variety of shapes in ETFE-foil constructions. As pneumatically pre-stressed foil cushions or as single-layer mechanically pre-stressed foil membranes, anticlastically or synclastically curved surfaces can be formed across nearly any ground plan. The feasible spans of the foil constructions vary according to the ground plan geometry, boundary condi-tions, construction system, and load effect.

In the extensive work of Moritz (Moritz, 2007), over 200 ETFE-foil proj-ects, built between 1980 and 2006, are documented. Six basic ground plan geometries can be identifi ed in the evaluated projects. Often these basic shapes are used in combination when implemented. Figure 6.20 depicts these six basic boundary geometries.

Evaluation of the more than 200 ETFE-foil projects in the indicated time period produces the percentage distributions shown in Figs 6.21–6.23:

• For ground plan geometries and type of construction, see Fig. 6.21• For project location according to countries and continents, see Fig. 6.22• For utilisation and application of structural elements, see Fig. 6.23.

The evaluations show that the ETFE-foil construction method had a dis-tinct concentration in Europe in the years between 1980 and 2006. Over 90% of the foil projects were built in Europe. In the last few years, however, increased application of foils as building envelopes can be observed in Asia. The backlog of demand in this region in the fi eld of foil construction is obvious. The Summer Olympic Games 2008 in Beijing with the construction

6.19 Olympic Stadium, Beijing (photo: V. Dangl).

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6.20 Basic boundary geometries of ETFE-foil constructions.

Boundary geometry

PolygonSystems without pre-stress

3%

2%

3%

4%

14%

17%

60%

Single-layer systems

mechanically pre-stressed

10%

Multi-layer systems

pneumatically

pre-stressed

87%

Rhombus

Circle, ellipsoid

Triangle, Trapezoid

Square

Rectangle

Pre-stress method

6.21 Distribution by percentage of ground plan geometry and type of construction of ETFE-foil constructions (evaluations of 200 ETFE-foil projects, time period 1980–2006).

Location (state) Location (continent)

HungarySlovenia

SingaporeMexicoJapan

IndiaGreece

DenmarkAustralia

ChinaUSA

FranceSpain

AustriaSwitzerlandNetherlandsGreat Britain

Germany

0.4%0.4%0.4%0.4%0.4%0.4%0.4%0.4%0.9%

0.9%0.9%1.3%1.8%2.6%3.1%

7.0%18.9%

59.0%

Asia 2.2%

Europe 95.5%

America 1.3%Africa 0%

Australia 0.9%

6.22 Distribution by percentage of project location according to countries and continents of ETFE-foil constructions (evaluations of 200 ETFE-foil projects, time period 1980–2006).

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of the Olympic Stadium and Swimming Pool complex were of central sig-nifi cance for the development of foil constructions in Asia.

Figure 6.23 regarding utilisation and application of the foils shows a distinct concentration in zoological, botanical or athletic facilities like indoor swimming pools or stadiums. For buildings with these kinds of utili-sation requirements, the building-physics characteristics of ETFE-foils offer more distinct advantages compared to conventional building materials.

6.5 ETFE-foils – morphology and production progress

The building-physics and mechanical behaviour of the foils are principally determined by their morphological structure. For this reason, the following section explains the morphology, production and resulting material behav-iour of ETFE-foils in sequence.

6.5.1 Defi nition of plastics and development of ETFE

ETFE as a fl uorine-polymer material belongs to the group of plastics. The term ‘plastic’ defi nes a technical (as opposed to natural) material consisting of macromolecules of organic groups. These are manufactured synthetically or semi-synthetically by chemical reaction (Frank, 2000). Therefore, plastics are part of macromolecule materials in general. The macromolecules are composed of numerous specifi c monomer units, which are covalently linked to long molecular chains. Plastics consisting of identical monomer units are named polymers. Copolymers, however, consist of different monomer units.

Utilisation Application

Offices, residential accommodation

Infrastructure (terminals, train stations)

Petrol stations

Sport facilities

Others (collectors, sculptures, etc.)

Schools, universities

Laboratories storage, greenhouses

Zoological gardens

Swimming pools

Museums, pavilions

2%

2%

4%

5%

Halls, pavilions

33%

Stadiums,

grandstands

2%

Other

applications

3%

Indoor

applications

5%

Façades,

windows

8%

Canopies,

walkways

14%

Atria, skylights

35%

8%

9%

10%

15%

18%

28%

6.23 Distribution by percentage of utilisation and application of ETFE-foil constructions (evaluations of 200 ETFE-foil projects, time period 1980–2006).

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The product ETFE was fi rst marketed in 1970 by the DuPont company under the name Tefzel®. According to DIN 7728, ETFE or E/TFE is the international abbreviation for ethylene-tetra-fl uorine-ethylene. Figure 6.24 shows the ‘plastic pyramid’ containing a few well-known thermoplastics. The pyramid classifi es thermoplastics depending on their temperature resis-tance and costs. ETFE is among the high-performance thermoplastics.

6.5.2 Morphology

The nonlinear viscoelastic material behaviour of ETFE depends substan-tially on the values of temperature and stresses and on the velocity of its exposure. Reasons for this behaviour are the morphological structure and the molecular confi guration of ETFE.

Confi guration and composition of the macromolecules

In general all polymers consist of long molecular chains. Figure 6.25 shows four different basic confi gurations of molecular chains (Ehrenstein, 1999). Linear, branched, crosslinked or tangle confi gurations of the molecular chains are possible. Confi gurations of crosslinked molecular chains have strong chemical bonds between the chains. Molecular chains with a tangle confi guration are linked together with less strong physical connections. The molecular chains of non-modifi ed ETFE have a tangle confi guration.

Two basic compositions of the macromolecules exist: amorphous and semi-crystalline compositions (Fig. 6.26). Molecular chains with an

High performance

plastics

Technical

plastics

300°C

150°C

100°C

Amorphous

PMMA PP

POM

PEPVC

PC

TPI

PTFE ETFEPVD

PS, SAN, ABS

PA 11, PA 12

PA 6-3-T

Semi-crystalline

Standard

plastics

6.24 The plastic pyramid.

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amorphous composition are positioned without a specifi c pattern. They are arranged in a disorganised manner. Molecular chains with a semi-crystalline composition are more structured with crystalline and amorphous areas. In the crystalline areas the chains are placed in parallel and form a crystal lattice. Non-modifi ed ETFE-foils have a semi-crystalline composition with a tangle confi guration of molecular chains. Semi-crystalline thermoplastics have a value of crystallisation between 30% and 70% (Menges et al., 2002). The value of crystallisation of a transparent ETFE-foil such as Nowofl on ET 6235 with a thickness of 50 μm is 32.64% (Böhme, 2005).

Classifi cation of plastics

According to DIN 7724 polymers can be classifi ed into three main groups: thermoplastics, thermosets and elastomers. The groups differ, for example, in confi guration of molecular chains, in deformation process and in tem-perature profi le of shear modulus. Figure 6.27 shows the three groups with their morphological structure and their solubility. Typical materials for each group are named.

ETFE-foils are part of the group of semi-crystalline thermoplastics. Their molecular chains have no chemical crosslinks. Therefore, ETFE-foils are meltable and weldable.

(a) (b) (c) (d)

(a) (b)

6.25 Basic confi gurations of macromolecules: (a) linear, (b) branched, (c) crosslinked, (d) tangle (according to Ehrenstein, 1999).

6.26 (a) Amorphous and (b) semi-crystalline compositions of macromolecules (according to Ehrenstein, 1999).

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6.5.3 Monomer units

The particular monomer units of polymers are produced by the petrochemi-cal processes of distillation of crude oil. During the distillation of crude oil the hydrocarbon molecular chains are divided into gas, benzin, diesel and heavy fuel. By cracking the crude benzin naphtha, very reactive hydrocar-bons are generated, especially the low-molecular-weight gas ethylene (C2H4). Ethylene is the starting material for the synthesis of ETFE and also for more than 30% of all petrochemicals. Ethylene is produced in great quantities during many petrochemical processes. Therefore, its production is extremely cheap. The second monomer unit of the ETFE is tetrafl uoro-ethylene (C2F4).

Non-modifi ed thermoplastic ETFE is a copolymer existing of approxi-mately 25% ethylene and 75% tetrafl uoroethylene. Figure 6.28 shows the structural formula of both monomer units of ETFE.

Plastics

Thermoplastic

Amorphous,

no crosslinks

Meltable,

weak soluble

Polyvinyl chloride

(PVC),

polytetrafluoroethylene

(PTFE),

polystyrene (PS),

polymethylmeth-

acrylate (PMMA)

Meltable,

strong soluble

Ethylene-tetrafluoro-

ethylene (ETFE),

tetrafluoroethylene/

hexafluoropropylene

(THV),

polyethylene (PE),

polypropylene (PP)

Not meltable,

insoluble

Epoxy resin (EP),

polyester resin (UP),

phenol resin (PF),

resorcin resin (RF),

polyurethane (PUR)

Not meltable,

insoluble

Styrene-butadiene-

rubber (SBR),

polybutadiene-

rubber (BR),

ethylene-propylene-

diene-rubber (EPDM)

Semi-crystalline,

no crosslinks

Not crystalline,

strongly crosslinked

Semi crystalline,

weakly crosslinked

Thermoset Elastomer

6.27 Classifi cation of plastics.

H

H

H

H

C = C

(a) (b)

F

F

F

F

C = C

6.28 Structural formulae of (a) ethylene (C2H4) and (b) tetrafl uoroethylene (C2F4).

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Polymers can be modifi ed by adding monomer units (so-called modifi er). For example, coloured ETFE-foils are modifi ed by adding supplementary masterbatches in order to achieve chromaticity. Besides, monomer units alter the linkage conditions between molecular chains. These alterations could result in a change of material properties of the polymers.

6.5.4 Production process

The production process of ETFE-foils can be divided into three basic steps: fi rstly copolymerisation, secondly drying and granulation, and fi nally extru-sion. Figure 6.29 shows the successive production steps of ETFE-foils to produce the fi nished product.

Copolymerisation

With copolymerisation the long-chain molecules are created. In a chemical reaction the two monomer units ethylene and tetrafl uoroethylene are linked together. Catalysts crack the carbon compound of the macromole-cules and hence additional monomer units can link. The product of copoly-merisation is an aqueous solution.

Drying and granulation

The second production step is drying and granulation. The aqueous solution of copolymerisation is transformed into granules by separation and drying. ETFE granules are frequently generated by a granulation machine as shown in Fig. 6.29. The solution of copolymerisation fl ows over a metal sheet. The temperature of the aqueous solution drops. At the end, traces of the solution are cut into pieces. The pieces are cooled, dried and fi nally formed into granules. The generated granules are easier to handle and easier to store than the aqueous solution of copolymerisation. At this point coloured granules or granules of recycled foils could be added.

Extrusion

The fi nal step is the extrusion of the ETFE-foil. In this step granules are processed to the fi nished rolled foil. The granules will be fi lled, e.g. into a single-screw extruder. Inside the extruder the granules melt. The screw transports the semi-fl uid material with defi ned velocity, temperature and pressure. The forming tool at the end of the extruder consists of a nozzle with a defi ned gap. The thickness of the produced fi lm depends on that gap. The width is defi ned by the length of the nozzles. Standard thicknesses of ETFE-foils are today 12 μm to 300 μm (0.012 mm to 0.30 mm). The width

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Monomer units

Catalist

Copolymer

Monomer

Starting reaction

Generation of

chains

Ethylene Modifier

Copolymerisation

Drying

Granulation

Extrusion

Finished product

Films

0

Granules

Powder

Aqueous solution

Tetrafluoro-

ethylene

6.29 Production process of ETFE-foils.

of the foil depends on the manufacturer, but foils are nowadays produced up to a width of 1.60 m.

6.6 Material properties

The material behaviour of ETFE-foils is extremely complex and differs fundamentally from that of textile membrane materials in regard to their thermal–mechanical as well as building–physics qualities. This section

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describes their building–physics, structural–chemical and mechanical characteristics.

6.6.1 Building–physics characteristics

Fire behaviour

According to DIN 4102-1, ETFE is fl ame retardant. It is classifi ed as B1. The melting point lies at approximately 275°C. When melting at this tem-perature occurs, roofs or facades made of ETFE-foils open up and thereby enable the venting of smoke or heat out of the building. The melted ETFE particles cool down and solidify very fast. According to DIN 4102-1, ETFE is considered to be a non-fl ammable dripping material, i.e. it drips without burning. Because of its extremely low self-weight (the self-weight of ETFE-foil with a thickness of 200 μm is about 350 g/m2) the thermal load of an ETFE-foil structure is very low.

Transmission of radiation

The optical characteristics of ETFE-foil are extremely advantageous. ETFE-foils have an especially high transmissibility for radiation. The trans-missibility of ETFE exceeds the values for glass or polycarbonate sheets. Values of transmission, refl ection and absorption vary with the number and inclination of the layers, the thickness and colour or printing of the foils. Light in the visible or white light spectrum (wavelength of radiation 400 nm to 750 nm) can be transmitted up to about 90%. The spectral distribution of the visible light spectrum is nearly constant with hardly any refraction occurring. Therefore, the intensity and quality of colours are retained inside a building, which is a major difference from glass, where the intensity and quality of colours is altered through refraction. Another major difference from glass or polycarbonate is the particularly high transmissibility of the ultraviolet (UV) spectrum. According to DIN 5031-7 the UV spectrum is classifi ed into three parts with different ranges of wavelengths:

• UV-A (low-energy, long-wave radiation, wavelength 320 to 400 nm)• UV-B (short-wave radiation, wavelength 280 to 320 nm)• UV-C (high-energy, very short-wave radiation, wavelength 100 to

280 nm).

The transmissibility of the total UV spectrum for ETFE considerably exceeds the values of glass or polycarbonate. Great differences of transmis-sibility occur, especially in the range of short-wavelengths less than 320 nm (UV-B and UV-C). In parts of these ranges ETFE-foils gain transmission factors exceeding around 70%. Most glass or polycarbonate sheets achieve factors of less than 20%.

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This higher transmission factor of UV radiation is one of the main favourable material properties of ETFE. UV radiation gives natural pro-tection against pests or bacteria. Especially the short-wavelength UV spectrum (UV-B and UV-C) abets the growth of plants. Microorganisms like bacteria, pests or vermin are eliminated by means of UV light. Because of their high transmissibility ETFE-foils are an optimal choice for the facades and roofs of greenhouses, zoological gardens, stadiums or swim-ming pools.

On the downside, the high transmissibility of the outer skin for high-energy radiation results in strong heating up of buildings with envelopes made of ETFE-foil. Therefore, such buildings often need extensive ven-tilation systems to facilitate the cooling of internal spaces. As an alterna-tive, light radiation can be absorbed and/or refl ected by white coloured or printed ETFE-foils, thereby preventing the overheating of interior spaces. Three layered ETFE-foil cushions with a curved middle layer and decoupled volumes make use of this technique. Printed middle and outer layers with inversely arranged patterns ensure a high degree of refl ection.

Noise and heat insulation

The noise insulation of ETFE-foil structures is limited by the low mass of the material itself. It can be improved by installing additional absorbing material fi xed, e.g., to the inside of the cushions. The acoustics of internal spaces depend critically on the noise absorption of the materials used. In this case the noise absorption of elastic ETFE-foils is better than that of rigid materials like glass. Therefore, foils (especially perforated foils) are sometimes used beneath ceilings or glass roofs as absorption materials. The propagation speed of noise can also be reduced by adding porous materials inside the cushions such as, for example, translucent aerogel particles of amorphous silicic acids. The crackling noise of raindrops on pre-stressed ETFE-foils can be reduced by using additional layers of grid membranes. The grid membrane as a fl eece layer is fi xed outside on the outer ETFE-foil layer. Crackling raindrops disperse and the noise is reduced.

In comparison to conventional materials for building envelopes, the heat insulation of ETFE-foil cushions is only moderate. It could be improved by using a dual-chamber system with a third middle layer and separated layers at the anchoring profi les (cf. Fig. 6.5: positions 5 and 6). A three-layer ETFE-cushion with two separated chambers achieves a U-value of approxi-mately 2.0 W/m2K. Hence, with separated or more layers the U-value can be improved.

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6.6.2 Structural–chemical characteristics

Durability

The durability of materials describes their resistance against exposure to chemicals or radiation in general. Insuffi cient durability of foils shows mostly in processes of expansion, softening or embrittlement of the mate-rial. This process is reinforced by higher temperatures.

ETFE-foils are frequently claimed to be alkali- and solvent-resistant. ETFE-foils used in the climatic conditions of building construction have very good resistance against most chemicals. Put in contact with chemical substances in normal concentrations, no expanding or softening should occur. When investigated according to DIN EN ISO 62:2008, ETFE foils showed no signifi cant alteration of dimensions due to water absorption.

By considering the fi rst ETFE-foil projects built at the beginning of the 1980s, the durability of ETFE-foils can now be determined over periods of more than 25 years under normal conditions. The investigation of naturally weathered ETFE-foils commissioned by the company Nowofol in the years 1979–1989 certifi ed this high durability of ETFE-foils. The tests were done at the D-SET laboratories in Arizona. The goal of the tests was to investi-gate the infl uence of UV radiation on tensile strength, ultimate strength, ultimate strain, tear strength and transmissibility of the foils. The uniaxial tests after radiation were done with new and naturally weathered foils. The foils were irradiated over different periods (up to 10 years). In summary the tests in Arizona determined that ETFE-foils have very high durability compared to other transparent plastic materials.

Tests to simulate the process of ageing with xenon radiation according to DIN EN ISO 4892-3:2006 confi rm the forecast that ETFE-foils have good durability over 25 years.

Anti-adhesive characteristic

The wettability of surfaces depends on their surface energy. High-energy surfaces or polar surfaces have a high wettability. On non-polar surfaces with low-energy characteristics, dirt can stick only with diffi culty. ETFE-foils have a non-polar surface. For example, the ETFE-foil ET 6235 shows a surface tension of approximately 25 mN/m (Hodann, 2007). Therefore, the smooth and non-polar surfaces of ETFE-foils show an anti-adhesive effect.

6.6.3 Eco-balance and recyclability

In contrast to composite materials, ETFE-foils can be recycled to almost 100%. ETFE granules from old used foils can be added back into the

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production process of other applications (downcycling). Because of the low self-weight of ETFE-foil structures, material can be saved in both primary and secondary structures. Therefore, the application of ETFE-foil structures helps to conserve natural resources.

6.6.4 Mechanical properties

The mechanical properties of ETFE-foils depend on climatic factors (espe-cially temperature), production factors (e.g. foil thickness, or quality) and loading effects (e.g. load history, load value and rate, time and stress condi-tions). Taking these factors into account, ETFE-foils exhibit a nonlinear viscoelastic material behaviour. Reasons for this behaviour are the morpho-logical structure and the molecular confi guration of ETFE.

Deformation behaviour and stress–strain curve

The complex deformation behaviour of ETFE-foils depends substantially on their morphological structure. The semi-crystalline structure is charac-terised by entanglement and fl exibility of the molecular chains. The whole deformation behaviour of ETFE-foils under exposure can be separated into three essentially different ranges:

1. A linear elastic deformation which is reversible. This deformation is the result of alteration of distance or of angles between atoms of the polymer.

2. A linear and non-linear viscoelastic deformation as result of stretching the tangle confi guration of the molecular chains. It is partly reversible depending on time.

3. A plastic deformation which is irreversible. This deformation process is the resu lt of sliding of one molecular chain in respect to another.

Figure 6.30 shows the stress–strain curve of uniaxial stressed ETFE foils qualitatively. The particular ranges of deformation are marked. It must be considered that the three different deformation ranges mentioned above exist almost throughout the progress of deformation. Therefore, it is diffi cult to separate deformation into individual rates. The deformation ranges inter-fere with each other, more or less. Figure 6.30 shows the dominating defor-mation behaviour for each range.

Three signifi cant characteristic points of the stress–strain curve are dis-tinguishable. The fi rst kink describes the elastic limit, the second kink is the yield strength and the third point describes the breaking point of the foil for uniaxial short term exposure. Up to the elastic limit, ETFE-foil shows an almost linear elastic behaviour. Hooke’s law prevails (at least for short-term loads). From the elastic limit point up to the yield strength, ETFE

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shows both linear and non-linear viscoelastic behaviour. After exceeding the yield point the material shows high viscoplastic deformation up to the breaking point. ETFE-foils have an enormous breaking strain. In uniaxial tests the breaking strain can be more than 350%.

6.7 Load-bearing behaviour of ETFE-foil structures

6.7.1 Factors of infl uence

The load-bearing behaviour of ETFE-foil structures shows distinctive mate-rial and geometrical nonlinearities. The structural behaviour of ETFE-foils is caused by the material properties and the deformation behaviour. Essential factors that infl uence the load-bearing behaviour are:

• Geometrical factors (e.g. sag, curvature of the foil geometry or ground plan geometry)

• Material factors (e.g. non-linear behaviour with elastic, viscoelastic and plastic ranges)

• Constructive factors (e.g. cushions with even or curved middle layer, additional cables, quality of welding seams and anchoring profi les).

6.7.2 Principal load-bearing behaviour of ETFE-foil structures

The resulting forces in ETFE-foils result directly from the relation between curvature of the foil geometry and loads. This relation can be defi ned for circular geometries with the boiler formula according to equation 6.1. Using the equation for a steel cable with uniaxial load-bearing behaviour, the cable force F is similar to the product of the load p multiplied by the radius of curvature r (cf. equation 6.1):

6.30 Uniaxial stress–strain curve of ETFE-foils (uniaxial test, qualitative diagram).

Tensile strength σu,k

Yield stress σy,k

Yield strain

3

2

1

Strain at break

First kink: elastic limit

Second kink: yield point

Linear and nonlinear-viscoelasticLinear-elastic

Breaking pointσ

Elastic limit σel,k

εy,k εu,k

εviscoplastic

εviscoelastic

εlinear elastic

ε

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F = rp 6.1

where the radius of curvature r is defi ned as the reciprocal value of the curvature κ.

The forces in ETFE-foil cushions can be calculated approximately by using the boiler formula, too. Equation 6.2 shows the boiler formula for a square ETFE-foil cushion stressed with an internal pressure p. The forces F1 and F2 in both axial directions are determined by considering both radii of curvature r1 and r2:

pFr

Fr

i = +1

1

2

2 6.2

This relation according to the boiler formula shows that if the radius increases the forces in the foil membrane will also increase. This means that forces in ETFE-foil cushions can be infl uenced by the choice of foil sag. With an increase of the internal pressure p the foil membrane of Fig. 6.31 will strain, the sag of the foil will increase and the radius of curvature will decrease. Therefore, ETFE-foil structures show a disproportionate rise of stresses when loads increase.

Loads, deformations and forces are already nonlinearly interdependent in the two-dimensional case. Therefore, the nonlinear equations to calculate the forces can only be solved iteratively. This non-proportional relation between loads, deformations and forces characterises the positive but complex load-bearing behaviour of ETFE-foil structures.

6.7.3 Load-bearing behaviour of ETFE-foil cushions under wind and snow loads

Wind suction loads

Figure 6.32 shows a cross-section of a two-layer cushion exposed to wind suction loads. The geometry of the cushion, the wind suction loads (ws), the

r1pi r2

F2

F1

6.31 Square ETFE-foil cushion under internal pressure, forces and radii of curvature.

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forces in the outer and inner layers (FOL, FIL) and the reaction forces at the anchoring profi les (Vr, Hr, Vl, Hl) are illustrated. For the pre-stress load case with internal pressure the sags of the outer and inner layers (fOL, fIL) are equal (if thickness dOL = dIL). The deformations of both layers under wind suction are described by ΔfOL and ΔfIL.

In general the effect of wind loads appears perpendicular to the surface. However, depending on the roughness of the surface, tangential wind loads can appear. In the case of very smooth membrane surfaces such as ETFE-foils these tangential loads can be disregarded.

For the calculation of ETFE foil cushions under wind loads, thermody-namic laws have to be considered. The investigation of the load-bearing behaviour under wind loads supposes that the molar mass of the air enclosed inside the cushion and the temperature during the exposure are approxi-mately constant. Therefore, the third gas law of Boyle–Mariotte with iso-thermal change of state according to equation 6.3 is used to analyse the structural behaviour. The third gas law of Boyle–Mariotte is:

p V p V pVpp

VV

1 1 2 21

2

2

1

= = = =const or. 6.3

Because of wind suction loads the outer layer will be lifted up, stressed and strained. Sag of the outer foil layer will increase about ΔfOL. Caused by the uplifting of the outer layer, the volume of the cushion will increase. According to the third gas law of Boyle–Mariotte the internal pressure must be reduced. Because of the decrease in internal pressure the difference in pressure at the inner foil layer will be reduced. Therefore, the inner layer will be discharged and the sag will decrease about ΔfIL.

pi

pi

ΔfOL

ΔfIL

fOL

fIL

FOL,V

HI

VI Vr

Hr

Ws

ROL

FOL

FOL,H

FIL,H

FIL

FIL,V

RIL

6.32 Principal load-bearing behaviour of a two-layer cushion under wind suction (according to Moritz and Schiemann (2008)).

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The load-bearing behaviour under wind loads shows that the wind suction loads are mostly supported by means of the outer foil layer. Figure 6.32 shows the deformed outer foil layer and the different resulting forces FOL and FIL in both foil layers. The forces in both layers can be separated into horizontal and vertical components as illustrated in Fig. 6.32. The equilib-rium in the vertical and horizontal directions at the anchoring profi les results from the reaction forces. The resulting vertical reaction forces (Vl, Vr) at each anchoring profi le are similar to the corresponding part of the vertical component of the wind suction load. The horizontal reaction forces result from the curved foil geometry of the cushion. These horizontal reac-tion forces are one of the principal structural differences between planar glass and curved foil structures. Therefore, horizontal stabilisations of primary structures of ETFE-foil constructions are often necessary.

Snow loads

The reverse of wind suction load is snow load. Snow pushes the outer layer down and the sag and forces in the outer layer are decreased. The inner layer will be strained under increasing internal pressure from snow load, sag, and forces will increase, too. Especially for high snow loads, the inner layer has to be supported by cables. Figure 6.33 shows the principal load-bearing behaviour under snow load.

6.7.4 Realisable spans of ETFE-foil structures

Because of the lower tensile strength of ETFE-foils in comparison to fabric membranes, ETFE-foil constructions, regardless of whether they are

pi

pi

ΔfOL

ΔfIL

fOL

fIL

FOL,VHI

VI Vr

Hr

s

ROL

FUL

FOL

FOL

FOL,H

FIL,H

FIL

FIL,V

RIL

6.33 Load-bearing behaviour of a two-layer cushion under snow load (according to Moritz and Schiemann (2008)).

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designed pneumatically or mechanically pre-stressed, cover shorter spans. However, if compared to glass construction spans those of ETFE-foil struc-tures are bigger.

The spans depend on various factors, like construction method (mechani-cally or pneumatically pre-stressed), construction type (one-layer or multi-layer systems), ground plan geometry, thickness of foil, load value and load history, and quality of foil and welding seams. Therefore, the following spans display only reference values.

For mechanically pre-stressed one-layer systems, spans of approximately 1.5 m are realisable. Spans of approximately 4.7 m are possible for pneu-matically pre-stressed foil cushions with rectangular ground plan and foil sag of 10% or more of their spans. In this case the length of the rectan-gular cushion is not decisive. For example, the verge cushions of the Masoala Rainforest Hall in Zurich (Fig. 6.13) have a length of about 106 m. For ETFE-foil cushions with circular or polygonal ground plan and sags of more than 10%, spans of approximately 7.5 m are realisable. Note that by using higher sags or additional structural elements like steel cables, cable nets or arches the spans of ETFE-foil structures can be increased.

6.8 Development potential of ETFE-foils in

architecture

Which development potentialities and application possibilities will ETFE-foil constructions offer for civil engineering and architecture in future? Are the large ETFE-foil projects of recent years, like the ETFE-foil cushions of the Allianz Arena in Munich or the bubble structure of the Water Cube in Beijing, only impressive examples of a current architectural philosophy? Or can the foil projects of the last few years be viewed as development steps towards the establishment of these construction methods within architecture?

Questions regarding future application potential of technologies can be answered by, among other things, analysis of the technology’s product cycle and life cycle, respectively. According to Bullinger, the life cycle of a tech-nology can be differentiated into four consecutive phases (Bullinger, 1994). The fi rst phase is referred to as pacesetter technology, in which high techni-cal uncertainties still exist and possible fi elds of application are largely unknown. This is followed by the second phase (key technology), in which the technical uncertainties disappear and the technology experiences an intensifi ed application. The possible fi elds of application increase continu-ously in this phase. In the third phase (basic technology) the technology is controllable and available at any time and nearly all fi elds of application are covered. In the fourth phase (superseded technology) the fi elds of

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application are noticeably decreasing and the technology is beginning to be superseded by competing products.

Which phase is the technology of ETFE-foils currently in regarding civil or structural engineering and what kind of potential does this construction method have in the future? At the beginning of the application of ETFE-foils in civil engineering in the 1980s and 1990s the behaviour and charac-teristics of the foil systems were predominantly examined in relation to projects. Many of the resulting insights were reserved for the performing companies, engineering offi ces, building authorities and checking engineers. Scientifi c evaluation and analysis of ETFE-foil constructions by indepen-dent research organisations such as universities and institutes for a long time were carried out only sporadically. In recent years, though, a noticeable change has been detectable in this regard. In the course of intensifi ed sci-entifi c research into the material and load-bearing behaviour of ETFE-foils, the results are now increasingly available to the general public.

Considering the cycle phases mentioned above and observing the devel-opment of foil construction, the ETFE-foil construction method can cur-rently be assigned to the phase of a key technology. The awareness level of the material as well as the construction method is continuously growing, the application fi elds are increasing, and the material as a building envelope is competing more and more with glass or fabrics.

6.9 Future requirements for architecture and civil

engineering

Further development of ETFE-foil construction from a key technology into a basic technology will be determined largely by economic, ecological, functional and architectural requirements for building construction. Besides production and maintenance costs, especially the factors of sus-tainability and reusability, energy consumption and the possibility of enabling large building-physics and design variations are included in this. Materials and construction methods, respectively, which are able to fulfi l these requirements due to their characteristics will be an integral part of architecture.

From an economic view, ETFE-foils are to be assessed positively. The production costs of foils are relatively low. Due to their self-cleaning surface properties, maintenance costs in the form of cleaning of the building enve-lopes are lower compared to glass. The energy costs for the stabilising pressures of pneumatic foil cushions are also relatively low due to the low pressures (ETFE-foil cushions constitute a low pressure system with pres-sures usually lower than 1000 Pa).

From an ecological perspective, sustainability of a construction method will certainly be of central importance in the future. What environmental

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compatibility and durability does a material have, what is its recyclability, and in which form can energy requirements best be fulfi lled? ETFE-foils are, as explained above, not composite materials. Therefore, they are highly reusable, can be almost 100% recycled and can be added back into the production process of other applications (downcycling). Due to the high transmissibility of the UV spectrum, ETFE-foils possess high durability and in this differ signifi cantly from many other polymeric materials.

Today, building envelopes and structural elements have to take on a variety of central functions. They determine the energy consumption and fundamentally dominate the overall impression of a building from a design perspective. In terms of the functional and architectural require-ments of the building envelopes, ETFE-foils offer interesting application possibilities.

From a building-physics perspective, the high transmissibility of the entire radiation spectrum is of fundamental importance. As already explained, the especially high transmissibility of the UV spectrum is already specifi cally utilised. Due to the high transmissibility of radiation, durability and self-cleaning surface properties, ETFE-foils are especially suited for the genera-tion of solar energy. The fi rst tests with fl exible photovoltaic cells placed between two ETFE-foil layers have already been done.

In future the relatively low heat insulation of ETFE-foil systems could be improved through combination with new technologies (e.g. translucent heat insulation, low-emission coating, etc.). Previous researches regard-ing this topic, e.g. by the use of translucent aerogel particles from amorphous silicic acids for heat insulation at simultaneous high light transmissibility, represent extremely interesting, but currently still very expensive solutions.

Nowadays, in the age of the digital world, communicative building enve-lopes represent the ideal advertising platform. Buildings can function directly as a company image for the building owner or user. In this context, due to their high optical transparency and high amount of fl uorine, ETFE-foils offer a variety of interesting development potentialities for devising informative and communicative building envelopes. Through integrated LED lighting mains in foil cushions (LeCuyer, 2008), or with the help of OLED surfaces laminated on top of ETFE-foils, the lighting functions can be further improved.

From a creative, engineering point of view, the feasible forms and maximum spans of ETFE-foil constructions are decisive factors which will determine the further success of this construction method. ETFE-foils possess positive load-bearing behaviour which is characterised by material and geometrical nonlinearities. The ground plan shapes, realisable to almost any desire, offer the architect a multitude of design possibilities. Spans of ETFE-foil constructions can be enlarged through support measures like

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cables, cable nets or laminated-in belts with only a small increase of self-weight.

It becomes clear that ETFE-foil structures can fulfi l many of the future aims and requirements for building envelopes. Furthermore, many new additional and innovative fi elds of application open up through the use of ETFE-foils. Thus, increasing application potential can be forecast for the use of ETFE-foils. However, a decisive factor in the further application and development of ETFE-foils is the differentiated consideration of their mechanical behaviour within the structural calculation. Research and tests of recent years have deepened knowledge of the complex mechanical behaviour of ETFE signifi cantly.

In 2004 Linke and Moritz, Engineering + Design GbR, developed a new static analysis concept of ETFE-foil structures for the AWD Arena project in Hanover. This concept considers the temperature dependency of the mechanical behaviour of ETFE-foils in combination with local meteoro-logical data for the fi rst time. In the doctoral thesis ‘ETFE-foil as structural element’ (Moritz, 2007) this concept was improved to a sophisticated struc-tural analysis concept for ETFE-foil constructions based on extensive mate-rial tests and evaluations. The concept has been applied successfully under different climatic conditions.

The mechanical behaviour of ETFE-foils under biaxial stress conditions and the load-bearing behaviour of ETFE-foil cushions in relation to mate-rial and geometrical parameters were investigated in the doctoral thesis ‘Load bearing behaviour of ETFE-foils under biaxial stresses’ (Schiemann, 2009).

In the next step the current knowledge of the mechanical and structural behaviour of ETFE-foils should lead to a generally valid structural design

6.34 Design of a single-layer ETFE-foil cupola with French trusses and steel cable net, Naturhistorisches Museum, Karlsruhe.

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concept. With such a design rule, ETFE-foil structures can develop into an established technology, i.e. a basic technology, within civil engineering and architecture. Based on its favourable properties and manifold practicability, this construction method most certainly possesses the potential for this (Fig. 6.34).

6.10 References

Böhme M (2005), Synthese und Charakterisierung von Protonenaustauschmem-branen durch strahlungsinduziertes Propfen auf Basis Sulfon-, Phosphor und Phosphonsäure, Technische Universität Clausthal

Bullinger H (1994), Einführung in das Technologiemanagement, Stuttgart, Teubner Verlag

Ehrenstein G (1999), Polymer-Werkstoffe, München, Carl Hanser VerlagFrank A (2000), Kunststoffkompendium, Würzburg, Vogel VerlagHodann R (2007), Fluorpolymer Folien für Architektur Konstruktionen, Der 5.

Baustoff – Bauen mit Membranen, Holzkirchen, wissenschaftliches Fachsymposium Fraunhofer Institut

LeCuyer A (2008), ETFE – Technologie und Entwurf, Basel, BirkhäuserMenges G, Haberstroh E, Michaeli W, Schmachtenberg E (2002), Werkstoffkunde

Kunststoffe, München, Hanser VerlagMoritz K (2007), ETFE-Folie als Tragelement, Dissertation, Technische Universität

MünchenMoritz K, Schiemann L (2008), Structural Design Concept, lecture notes, First

Master Program for Membrane Structures, Hochschule Anhalt, Dessau, GermanySchiemann L (2009), Tragverhalten von ETFE-Folien unter biaxialer Beanspruchung,

Dissertation, Technische Universität München

6.11 Appendix

Lion House, Hellabrunn Zoo (Fig. 6.7)

Location: MunichCompletion: 1994Architect: Herbert Kochta, MunichStructural engineer of primary structure: Schlaich, Bergermann und Partner,

StuttgartStructural engineer of membrane structure: IPL, Radolfzell; Schlaich,

Bergermann und Partner, StuttgartMembrane structure: Koit/Koch Hightex GmbH, Rimsting

Moveable ETFE-foil cushion (Fig. 6.8)

Location: Olympic Park, MunichCompletion: 1996Architect: Behnisch & Partner, Stuttgart

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Structural engineer of primary structure: Posselt Consult, Übersee/ChiemseeStructural engineer of membrane structure: Tensys Ltd, BathMembrane structure: Koit/Koch Hightex GmbH, Rimsting

Thermal Baths, Prien (Fig. 6.9)

Location: Prien at Lake ChiemseeCompletion: 1999Architect: Zeller & Romstätter, TraunsteinStructural engineer of primary structure: Zeller, TraunsteinStructural engineer of membrane structure: Tensys Ltd, BathMembrane structure: Koch Membrane Structures, Rimsting

Cycle Bowl (Fig. 6.10)

Location: Expo HanoverCompletion: 2000Architect: Atelier Brückner, StuttgartStructural engineer of primary structure: Dr Grotkop und Partner, BremenStructural engineer of membrane structure: Dr Grotkop und Partner,

Bremen and IPL, RadolfzellMembrane structure: Vector Foiltec Group, London/Bremen

Garden of Eden (Fig. 6.11)

Location: St Austell, CornwallCompletion: 2001Architect: Nicholas Grimshaw & Partners, LondonStructural engineer of primary structure: Anthony Hunt Associates, LondonStructural engineer of membrane structure: Anthony Hunt Associates,

LondonMembrane structure: Vector Foiltec Group, London/Bremen

Information Centre, Walchensee Power Station (Fig. 6.12)

Location: Kochel am SeeCompletion: 2001Architect: Hausschild & Boesel, MünchenStructural engineer of primary structure: Planungsgesellschaft Dittrich,

MünchenStructural engineer of membrane structure: Engineering + Design Linke

und Moritz, RosenheimMembrane structure: covertex GmbH, Obing (now seele cover GmbH)

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Masoala Rainforest, Zürich Zoo (Fig. 6.13)

Location: ZürichCompletion: 2002Architect: Gautschi + Storrer, ZürichStructural engineer of primary structure: MWV, Zürich and ABT, ArnheimStructural engineer of membrane structure: Engineering + Design Linke


Conference Building, Bundesstiftung für Umwelt (Fig. 6.14)

Location: OsnabrückCompletion: 2002Architect: Herzog + Partner, MünchenStructural engineer of primary structure: Barthel & Maus, MünchenStructural engineer of membrane structure: Barthel & Maus, MünchenMembrane structure: B&O Hightex, Breitbrunn

Allianz Arena (Fig. 6.15)

Location: MunichCompletion: 2005Architect: Herzog & De Meuron, BaselStructural engineer of primary structure: Arup GmbH, Berlin and Sailer

Stepan und Partner, MunichStructural engineer of membrane structure: Engineering + Design Linke


AWD-Arena (Fig. 6.16)

Location: HanoverCompletion: 2005Architect: Schulitz & Partner, BraunschweigStructural engineer of primary structure: RFR, Stuttgart and Weyer,

DortmundStructural engineer of membrane structure: Engineering + Design Linke


Atrium Roof IABG (Fig. 6.17)

Location: OttobrunnCompletion: 2005

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Architect: WSSA GmbH, MünchenStructural engineer of primary structure: Posselt Übersee/Chiemsee and

BWP, MünchenStructural engineer of membrane structure: Engineering + Design Linke


National Swimming Centre, Beijing (Fig. 6.18)

Location: BeijingCompletion: 2008Architect: Peddle, Thorpe & Walker (PTW)Structural engineer of primary structure: Arup GmbH and CSCEC + DesignStructural engineer of membrane structure: Vector Foiltec Group, London/

BremenMembrane structure: Vector Foiltec Group, London/Bremen

Olympic Stadium, Beijing (Fig. 6.19)

Location: BeijingCompletion: 2008Architect: Herzog & De Meuron, BaselStructural engineer of primary structure: Arup GmbH and othersStructural engineer of membrane structure: covertex GmbH, Obing (now

seele cover GmbH)Membrane structure: covertex GmbH, Obing (now seele cover GmbH)

Design of Cupola Naturhistorisches Museum, Karlsruhe (Fig. 6.34)

Location: KarlsruheStructural design: Brengelmann, Novacki, Schiemann

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229

7Tensile structures – textiles for

architecture and design

J. CHILTON, Nottingham Trent University, UK

Abstract: In this chapter mainly tensile textile structures used for the roofi ng of small, medium and large enclosures are considered, although the principles outlined apply equally to facades, and to textile structures in interior design and art. Commencing with a brief history of the development of modern tensile structures, the general principles (structural effi ciency, typical materials, form-fi nding, patterning, fabrication, installation and pre-stressing) are discussed. Physical and environmental properties and other factors that infl uence the aesthetic and architectural perception of tensile structures and the spaces they enclose, for example translucency, thermal performance, acoustics and lighting, are also reviewed. Case studies of selected architectural, interior design and art projects are presented to illustrate recent practice. Finally, future trends are identifi ed and a selection of further sources of information and advice is given.

Key words: tensile structures, fabric architecture.

7.1 Introduction

The concept of fabric architecture originates in the tent, principally a form of portable shelter used throughout recorded human history. Nevertheless, despite many similarities, modern tensile surface structures used in architecture and design exhibit a different level of technological and design sophistication, not least due to the improved durability, ver-satility and strength of modern coated and uncoated fabric materials.

In this chapter the main concern is with tensile textile structures used for the roofi ng of small, medium and large canopies and enclosures, although the principles outlined apply equally to facades and interiors, and to textile structures in art and design. Commencing with a brief history of the development of modern tensile structures, the general prin-ciples (structural effi ciency, typical materials, form-fi nding, patterning, fabrication, installation and pre-stressing) are discussed. Physical and envi-ronmental properties and other factors that infl uence the aesthetic and architectural perception of tensile structures and the spaces they enclose, for example translucency and light, thermal performance and acoustics, are also reviewed. Case studies of selected architectural and art and design

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projects are presented to illustrate recent practice. Finally, future trends are identifi ed and a selection of further sources of information and advice is given.

7.2 Brief history and development of tensile

structures

Tents and similar covered frames such as the Arab black tent, tepee and withy have been known throughout recorded human history and used as a form of lightweight and portable shelter. On a larger scale, the Romans are known to have used retractable textile shading devices, ‘velaria’, to shield audiences from intense sunlight in many of their arenas (Campioli et al., 2007) and this tradition continues to this day in Mediterranean countries with the use of ‘toldos’ in, for example, southern Spain. Technological devel-opments in weaving in the nineteenth century facilitated fabrication of large transportable tents, as used by travelling circuses (Forster and Mollaert, 2004, p. 26) and the military. However, the widespread adoption of tensile surface structures in architecture, for more permanent construction, is a more recent phenomenon.

It is generally recognised that the major contributor to the develop-ment of contemporary tensile architectural structures is the German architect Frei Otto (Nerdinger, 2005; Scheuermann and Boxer, 1996; Drew, 1976). Inspired by Severud and Nowicki’s long-span, cable-supported roof for the Raleigh Livestock Arena, North Carolina (1953), and working with tent maker Peter Stromeyer, from the mid-1950s Otto experimented with and refi ned designs for free-form, double-curved textile architecture. Perhaps his best-known works are the cable net roof structures for the German Pavilion erected for the Montreal Expo ’67 (with Rolf Gutbrod) and the Munich Stadium for the 1972 Olympics (with Günter Behnisch). The former supported around 10,000 m2 of PVC-coated polyester fabric, tensioned to form the enclosure, whilst the latter mainly carried trans-parent acrylic tiles (Forster and Mollaert, 2004, p. 27; Scheuermann and Boxer, 1996, pp. 1–7). Signifi cant contributions have also come from others, such as Walter Bird and Horst Berger who developed one of the earliest striking examples of a long-span textile roof being supported solely by internal air pressure within the building, the US Pavilion for the Expo ’70 in Osaka and the membrane-clad tensegrity domes of the Seoul Olympics, 1988 (Berger, 1996). Thanks to the infl uence of these pioneers, the latter half of the twentieth century and the start of the twenty-fi rst century have seen a massive increase in the use of tensile fabric architecture, which has necessitated a dramatic change in concep-tual design thinking and in the perception of the permanence of construction.

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Tensile structures – textiles for architecture and design 231


7.3 Concept of fabric architecture

With the advent of tensile and fabric architecture came a freedom of form which had been generally either lacking or diffi cult to achieve with more traditional structural materials such as timber, masonry, steel and reinforced concrete. Perhaps for the fi rst time, as described in Section 7.4, designers were confronted with a lightweight, deformable, structural envelope which to some extent defi nes its own contour but where an almost infi nite variety of shapes is possible. It is diffi cult to adequately describe such forms with just plans, elevations and sections. Therefore, perhaps even more than usual, architects are compelled to conceive and visualise their designs fully in three dimensions, with physical and/or computer-aided design models.

A broad classifi cation of tensile membrane architecture is suggested by Bradatsch et al. (2004, pp. 68–82) in the European Design Guide for Tensile Surface Structures (Forster and Mollaert, 2004). It categorises tensile surface structures in a matrix according to three different applications (covering, internal or attached), which may be described more fully as external and independent, internal, or external and attached to other build-ing construction, and three different modes of enclosure (open, enclosed or convertible), the latter being some form of fully or partially retractable membrane. However, the majority of tensile membrane structures fall into the ‘open covering’ category, where they are used as open roofs or canopies: see Fig. 7.1.

7.4 General principles of tensile structures

Before describing the use of textiles for tensile structures in architecture and design it is important to explain how the structural behaviour of fl exible

7.1 A typical tensile membrane structure of the ‘open covering’ type (photo: John Chilton).

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elements – cables, membranes and cable nets – differs from that of more conventional structures.

There is a hierarchy in the manner in which structures resist loads applied to them, with elements in pure tension being the most effi cient. Their full cross-section can be stressed at or close to the material’s ultimate strength, unlike elements loaded in pure compression, which generally suffer from buckling instability well before stresses reach that level. Also less effi cient are beams, where both tension and compression stresses occur in bending and, due to their distribution pattern within the beam section, much of the material is underutilised. Fortunately, most of the materials commonly used in construction, including natural and man-made yarns and textiles, have good tensile strength, though brick, stone and unreinforced concrete are notable exceptions.

This means that even highly fl exible elements with negligible bending stiffness, such as chains, cables, ropes, yarns and woven fabrics, can be used effectively in the most effi cient structures, those stressed in pure tension. Assuming that they are subject only to gravitational loads, they are nor-mally straight only when hanging vertically. Any inclination from the verti-cal produces some defl ection under self-weight. This forms a curve, known as a catenary. Any additional applied load will cause a change in shape of this hanging profi le. These effects can easily be seen in a spider’s web when loaded with early morning dew (Fig. 7.2).

7.2 Spider’s web loaded with dew (photo: John Chilton).

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The most common use of tensile structures in architecture is in roof structures, which are subject to variable and dynamic loads, including wind uplift. Therefore, when lightweight fl exible structural roof systems, such as cable nets or membranes, are used, fl utter may occur. To stabilise the struc-ture one could install additional dead weight, so that deformation under dynamic loads, in use, will be minimal. For example, in a suspension bridge the relatively heavy bridge deck stabilises the main cables so that the vari-able traffi c and wind loads normally induce only small movements (the wind-induced collapse of the Tacoma Narrows Bridge in November 1940 being an infamous exception). However, for tension structures in architec-ture and design this strategy negates what is probably their most important characteristic, their lightweight appearance. To maintain that visual delicacy additional lightweight elements may be used to stabilise the structure. For example, for a hanging cable in a roof structure it is common to add a cable of opposite curvature (above, below or intersecting) linked at several points along each cable with ties or struts, as appropriate, to form a cable truss. The fi rst cable will then support the roof self-weight, downward wind pres-sure and snow load, whilst the opposing cable will resist upward wind suction forces.

For tensile surface structures, such as membranes and cable nets, two sets of yarns or cables (usually approximately parallel and orientated orthogo-nally) fulfi l these roles. The yarns are effectively linked by weaving and the cables by clamps at intersections, and form an anticlastic surface in three dimensions. At any point this type of surface has opposing curvatures in two perpendicular directions (i.e. one concave and the other convex). It should be noted that, as three points always lie on a fl at plane, to achieve an anticlastic surface requires a minimum of four support points, one of which must be out of plane. The most common ways of forming anticlastic surfaces are with the conic, saddle/‘hypar’, arch supported, and ridge and valley (or wave), as shown in Figs 7.3 (a) to (d).

Double-curved surfaces in pure tension may also be achieved by infl ation e.g. soap bubbles, balloons and car tyres. However, these are synclastic forms where the curvatures in two perpendicular directions are the same (i.e. either both concave or both convex).

7.5 Design development – form-fi nding, patterning

and pre-stress

Design development is an iterative process. Unlike the tents of old, modern tensile structures are normally expected to display a smooth, unwrinkled surface under all expected loading conditions and whilst, at times, undergo-ing substantial displacements. This requires accurate determination of the form; precise patterning, cutting and assembly of the material; detailing of

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connections; and the introduction of an appropriate level and distribution of pre-stress into the surface once erected.

7.5.1 Form-fi nding

Because of the nature of tensile surface structures it is not easy for the architect, designer or artist to visualise accurately the fi nal form. The shape cannot be arbitrarily determined but is, in effect, self-determining. It results from several factors, over some of which the designer may have little or no control, for instance:

• Disposition of support points• Applied load at any instant• Properties of the fabric• Distribution of applied pre-tension.

At the conceptual design stage, soap fi lms (which are uniformly stressed tensile surfaces) developed within a combination of rigid (e.g. wire frame) and/or fl exible (e.g. cotton thread) boundaries, may be used (Otto and

(a) (b)

(c) (d)

7.3 Anticlastic surfaces: (a) conic; (b) saddle/‘hypar’; (c) arch supported: (d) wave form (photos: John Chilton).

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Rasch, 1995, pp. 58–59). More commonly, a scale model may be con-structed, for instance with stretch fabric (Fig. 7.4), to give some idea of the surface form. However, as the latter allows non-uniform stress in the surface – the fabric may be stretched more between some boundary points – it may not give a true representation of the fi nal built form unless the differential stressing is reproduced in the full-scale structure. However, using computer-aided design techniques such as the force-density method or dynamic relax-ation, given the relevant input data (such as support locations, material mechanical properties, applied loading and distribution of pre-stress), engi-neers are able predict the resulting three-dimensional surface with reason-able accuracy.

From a practical viewpoint, it should be noted that for external tensile structures it is important to consider the possibility of ‘ponding’ due to accumulation of snow and/or rainwater on fl atter surfaces or areas com-pletely enclosed by higher areas. Potentially, this may cause local failure of the membrane surface or even the whole structure, due to overloading. Therefore, the designed form should ensure that this cannot occur or alter-native provision should be made to remove excess rainwater or snow from vulnerable areas of the surface.

Once the preferred three-dimensional surface has been generated, it is analysed structurally to determine the expected stresses and deformations and the loads that it will transfer to the supporting structure. The surface then has to be patterned and manufactured.

7.4 Conceptual scale model constructed with stretch fabric (photo: John Chilton).

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7.5.2 Patterning and assembly

The textile materials used in tensile membrane structures are manufac-tured in rolls of different and predetermined widths, typically in the range 1.5 m to 3.6 m, depending on the manufacturer, type of fabric and coating. However, to create the textile structure, the fabricator has to convert these essentially fl at materials into one or more large double-curved continuous surfaces. Just as a tailor or dressmaker creates a suit or dress to fi t the complex curved form of the human body by using smaller pieces of material – cut from fl at fabric using a pattern, then sewn together to make a garment – so the textile structure designer and/or fabricator must determine an appropriate cutting pattern for fl at strips of the membrane material to be assembled into the double-curved three-dimensional surface.

During this process the designer must take into account the anisotropic nature of the fabric which results from the differential tension of the yarns in the warp and weft (or fi ll) directions. Where possible, the principal stresses determined in the structural analysis of the surface, following form-fi nding, are aligned with the directions of the warp and weft yarns. Defects such as bow and skew must be considered and appropriate allowance made for them in the assembly process (compensation for differential stretch of the fabric during pre-stress, seams for welding, etc.). The patterned panels tend to be long thin strips with curved boundaries (see Fig. 7.5) and the tighter the radius of curvature of the surface the narrower the strips tend to be.

Selection of the cutting pattern may have a considerable effect on mate-rial use and cost of the construction. It is important to minimise the waste remaining from the roll following cutting and to keep the number and length of seams to a minimum. Apart from considerations of strength, assembly and economy, it may also be necessary to review the number and

7.5 Patterned panels of long thin strips with curved boundaries (photo: John Chilton).

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disposition of the seams from the architectural and aesthetic point of view. This issue is discussed in more detail in Section 7.6.2.

As the fi nal construction is normally expected to be water- and airtight, most commonly, seams between individual pieces are made by fusing the coatings of overlapping edges using heat or high-frequency welding, usually in the fabrication workshop. The seam strength is dependent on the bonding of coating to base fabric and the width and quality of weld. However, seams may also be made by gluing and mechanically by stitching, lacing or clamp-ing between metal plates or timber strips. The former is often used to connect prefabricated panels on site and depends on the incorporation of a ‘bolt rope’ or ‘keder’ in a sleeve along the edges to be joined.

Once assembled, the fabric panels/fi elds have to be packed carefully to avoid creasing of the membrane, which may potentially initiate tears at a future date, for transportation to site.

7.5.3 Pre-tension

Initially the membrane panels are suspended from the predetermined support points. They are then stretched between the boundaries, which may be fi xed (e.g. rigid elements of the supporting structure) or fl exible (e.g. edge cables) (see Fig. 7.6), usually by means of mechanical or hydraulic jacking systems. For instance, for wave forms, the membrane surface may be stressed by tensioning the ridge and/or valley cables between adjacent cables. This introduces the design pre-stress to tension, smooth and stabilise the surface. To achieve this, the membrane panel is most commonly manu-factured to dimensions slightly smaller than the fi nal required pre-stressed surface, by a percentage predetermined according to its material properties – a process known as ‘compensation’.

Whatever the mode of introduction of pre-stress, due to the relaxation and creep behaviour of architectural fabrics, it is necessary to check the level of pre-stress periodically and to re-stress, as appropriate, to maintain the form and designed performance of the surface.

7.5.4 Assembly and construction details

Tensioning the membrane surface usually involves connection to a system of masts, cables, belts, clamps, plates and anchorages. As the means of con-nection of the surface may affect its form and behaviour, simple fl exible minimal boundary elements are preferred. As well as infl uencing the struc-tural performance of the membrane surface, often the quality of installation and connection details, and the way in which they relate to the membrane surface, determines the architectural/aesthetic success or failure of the realised design.

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(a)

(b)

7.6 Typical boundary cable fi xing details at Dynamic Earth, Edinburgh (photos: John Chilton).

Edge details

Edges may be either fl exible or rigid and both are obliged to transfer normal and tangential forces. Various confi gurations can be used for fl exible edges and employed to introduce the pre-stress into the surface by tension-ing the boundary element, for example:

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• Loose cable in a continuous welded edge pocket• External cable linked to the edge by straps and/or clamp plates• Woven textile belts stitched or welded along the perimeter

(Houtmann and Werkman, 2004, p. 156). In the case of rigid edges lacing and clamping are used.

Point supports

Anticlastic surfaces are generally stressed between a series of high and low points, at which the surface forces become concentrated. To prevent the point support from punching through the membrane it is necessary to distribute the concentrated reaction into the surface as smoothly as possi-ble. This may be accomplished by means of details such as mast rings, ‘umbrellas’ and ‘tear drop’ cable loops.

Corners

Point supports often coincide with a corner, or junction, between two or more boundary cables. Because of the many functions they have to perform (carrying the weight of the fabric and forces in the edge cables, restraint of tangential forces, adjustability/fl exibility/freedom of movement, attachment of lifting and tensioning devices) these are perhaps the most diffi cult con-nections to detail. They also need to be designed to minimise force eccen-tricities. This is an area where good communication between engineer and architect/designer is essential if an aesthetically elegant but high-performance detail is to be achieved.

Safety

Construction details also infl uence the membrane structure’s resistance to vandalism and damage. It is important that the support system is designed to be stable without the membrane in place, for example in the case of fl ying-masts supporting high points in the membrane, where, if the mem-brane is damaged, they could potentially swing down and cause injury to occupants unless a secondary support system is in place.

Rainwater run-off

As membrane roofs often cover considerable areas, where necessary, it is advisable to provide appropriate channels to safely discharge rainwater. This may be achieved by attaching a foam-fi lled roll of fabric slightly inwards of the edge to guide run-off to downpipes, thus avoiding inadver-tent, and sometimes embarrassing, showers. Alternatively, low points in the membrane surface may act as funnels to discharge rainwater (Fig. 7.7).

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7.6 Common materials and their architectural

properties

7.6.1 Material types

Typical fi bres and the main types of textiles and coatings used for construc-tion are described in detail in other chapters. Nevertheless, it is useful to note here that the two most common fabrics currently in use for textile membrane structures are PVC-coated polyester (PVC/PE) and polytetra-fl uoroethylene Tefl on®-coated glass cloth (PTFE/glass). Both materials resist soiling but the PTFE coating performs better in this respect. PVC/PE fabric is generally cheaper than PTFE/glass fabric although usually less durable. It is also more fl exible, making it more suited to deployable mem-brane structures. To improve the translucency of the material, different weave patterns and densities may be used and alternative coatings such as silicone may also be applied. Higher translucencies may also be obtained, for instance with woven PTFE fabrics such as Gore’s Tenara used recently

7.7 Rainwater discharge funnel (photo: John Chilton).

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in the retractable roof over Wimbledon’s Centre Court, which has a trans-lucency in excess of 30% (Gore, 2009).

Because of its high translucency (approximately 95% over a wide spec-trum) there is a growing tendency to use ETFE (ethylene-tetrafl uoro-ethylene) foil either in place of, or in combination with, coated woven textiles. Illustrations of a selection of membrane and foil materials and coatings, and a table giving an overview of properties, are presented by Pudenz (2004).

7.6.2 Light

The perception and readability of tensile fabric structures is very dependent on the optical properties of the material – the way it refl ects, absorbs or transmits visible light. Apart from their low self-weight, typically between 0.5 and 1.5 kg/m2 for a single layer, one of the most important characteris-tics of textile structures in architecture is their translucency, which varies according to the fabric weave, density and type of coating used. Typically PVC/PE and PTFE/glass fabrics have translucencies ranging from 5% to 25%, for a single layer of fabric, with the remaining light mainly being refl ected. However, they can be given completely opaque coatings, and uncoated mesh fabrics may have translucencies as high as 95% (Pudenz, 2004).

For a two-layer system the overall transmittance Tm is:

Tm = T1T2/(1 − r1r2) 7.1

where

T1 = transmittance of the external layerT2 = transmittance of the internal layerr1 = refl ectance of the inner surface of the external layerr2 = refl ectance of the outer surface of the internal layer(Chilton et al., 2004, p. 106).

Ironically, despite the resulting relatively high daylight factors in the interior (usually considerably higher than most typical interiors lit by windows around the perimeter) and at consistent levels over a much larger area, there is commonly a perception that the interior of membrane-covered enclosures can be rather gloomy. This is a consequence of the generally diffuse nature of the light penetrating the membrane, which limits the defi nition of shadows normally used by the human eye to differentiate objects, and the contrast between the very large area of bright fabric over-head and the duller wall and fl oor surfaces at low level (even though they are more brightly illuminated than typical naturally lit interior surfaces). To some extent this may be overcome by the use of glazed skylights set

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into the membrane surface to introduce directional sunlight and create distinct shadows (Chilton et al., 2004).

A similar effect occurs on the outside of the enclosure where, unless shadows, for instance from masts and cables, are cast on the membrane surface, its contours may not appear well-defi ned.

Internal illumination, for instance by uplighters, can be used highly effec-tively to highlight the surface curvature and increase the readability of the form. At night, light refl ected off the inner curved surface of the membrane is dispersed throughout the enclosure. Simultaneously, transmittance through the membrane surface allows the enclosure to become an illumi-nated beacon in the landscape.

For interior design, membranes may provide free-form, translucent or light-refl ecting surfaces to manipulate natural daylight or artifi cial light within a space. Equally they may be used as fl exible projection surfaces for light shows, fi xed images or videos. They may also be used to create innova-tive diffusers for internal light sources.

Strongly related to the transmittance of light through the membrane surface and readability of the form, both architecturally and aesthetically, the disposition of the welded seams can be very important, as the human eye accentuates the contrast between the light membrane and darker over-lapped seams. Therefore, due to the translucent properties of most textile materials, the pattern of the seams will be highly visible on the inside of the enclosure during the day and on the exterior at night: see Fig. 7.8. Although this tends to reinforce the viewer’s perception of the form’s curvature, a poorly selected cutting pattern may, equally, detract from the enjoyment of a carefully sculpted surface.

7.6.3 Thermal performance

The positive characteristic of high light transmittance acts against tensile fabric structures in terms of their thermal and acoustic performance. A single layer has a typical quoted thermal conductance or U-value of between 4.5 and 6.4 W/m2K, depending on its thickness, material composition, loca-tion and orientation. Due to the very limited thickness of the material (typically between 0.2 and 1.5 mm), much of this value is due to the sum of the internal and external surface resistances. Equally, the limited thickness means that the surface reacts rapidly to changes of incident radiation, heating up quickly with direct sunlight and cooling, often well below ambient air temperature, by direct radiation to the cold night sky (Devulder et al., 2007a). This can lead to condensation on the inner surface, particularly in the hours immediately before sunrise, especially in winter, when in colder climates the condensation may manifest itself as frost or ice. In some enclo-sures the condensation may be suffi cient to cause water droplets to form

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(usually on more inclined surfaces) and potentially to run down the surface and drop off at details such as seams, into the enclosed space below (Devulder et al., 2007b).

Effectively, an uninsulated membrane roof often performs as a large hot or cold radiator suspended over the whole fl oor area that it covers, with consequences on the comfort of the space’s occupants. The use of a double-layer membrane mitigates this to some extent but does not fully overcome it. Therefore, with growing awareness of energy effi ciency in buildings and the effect on climate change, this has tended to limit the use of uninsulated membranes to spaces classifi ed as unheated enclosures. However, new translucent/transparent insulation materials and fabric coatings to reduce emissivity (some described in Section 7.8) are beginning to improve the thermal performance of membrane construction, allowing it to be used more widely for covered and heated enclosures.

7.6.4 Acoustics

Textile membranes are thin, low-mass structures. This means that they provide little acoustic insulation, although micro-perforated foils in combi-nation with other membranes may provide substantial acoustic absorption (Pudenz, 2004, p. 60). The tensioning of the membrane surface means that at times of heavy rain or hail, although these are usually of short duration, skin drumming occurs. This phenomenon is even more pronounced with infl ated ETFE cushions.

7.6.5 Fire resistance

Since their introduction there has been considerable debate about the behaviour of the various membrane materials in fi re, including the toxicity

7.8 Pattern of welded seams seen from the inside of a membrane roof at the Palenque, Seville, Spain (photo: John Chilton).

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of fumes given off during combustion. For PVC/PES membranes between 160˚C and 250˚C the material melts away from the heat source to produce holes which release heat and smoke from the enclosure. Fire retardants incorporated in the coating ensure that they self-extinguish on removal of the fl ame. PTFE-coated glass material is considered non-combustible but at temperatures, around 270˚C seams may open, with the same benefi cial effect as the holes in the PVC/PES fabrics. Modern silicone-coated glass fabrics have similar performance to that of PTFE/glass (Huntington, 2004). Due to the production of toxic fumes from PTFE at high temperatures, sprinkler systems or appropriate mechanical ventilation may be required where PTFE/glass fabrics are used within enclosed spaces.

7.7 Applications and examples of tensile structures

To illustrate some of the properties and uses of tensile fabric structures, a series of examples have been selected, covering various design fi elds: archi-tecture, interior design and art.

7.7.1 Architecture – roofs, canopies and facades

An architectural practice that has exploited the translucency and expressive form of textile roofs to develop a distinctive style and elegance for many of their projects is Hopkins Architects, an early example being the Schlumberger Research Centre, near Cambridge, completed in 1984. This was the fi rst large-scale architectural use of PTFE/glass fabric in the UK (Sheuermann and Boxer, 1996, p. 114). Here, as in several of their mem-brane roof projects, the strategy is to not rely wholly on the translucency of the textile surface, which, as noted in Section 7.6.2, tends to impart a diffuse light to the interior and often appears quite dreary, but to include glazed roof lights of various forms to allow the penetration of direct sun-light (Hopkins Architects, 2008a). This is well demonstrated in the Dynamic Earth, Edinburgh, 1999 (Hopkins Architects, 2008b), where four lenticular, glazed roofl ights are suspended from cables around the main supporting masts, as seen in Figs 7.9(a) and (b). These alternate with steel arches, also suspended from the masts, to carry the saddle surface.

Internationally, perhaps one of the best known and largest textile roof enclosures is the O2 Arena (previously the Millennium Dome) in London, originally constructed to house the Millennium Experience in 2000 (Barnes and Dickson, 2000; Liddell, 2000). Although the overall shape of the 356 m diameter, 50 m high roof approximates to a dome, this is created by sus-pending a tensioned cable net of approximately that form, from 100 m high masts arranged in a 200 m diameter circle (Koch, 2004, p. 226). The cable net is clad with PTFE/glass fabric panels, which have only a small degree

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of double curvature, and an internal liner membrane was provided to reduce the formation of condensation (Koch, 2004, p. 227): see Figs 7.10 (a) and (b).

Previously, the largest roof of this type, elliptical in form, was that used to cover the 240 m × 193 m clear span Georgia Dome in Atlanta, USA, completed in 1992 (Terry, 1994). However, in this case the PTFE/glass fabric panels have more pronounced double curvature and are supported by a deep ‘hypar tensegrity’ cable dome tensioned within a perimeter concrete ring beam (Figs 7.11 (a) and (b)).

A spectacular example of a ridge and valley textile structure, 320 m in length, covers the central concourse of Denver Airport Terminal (1994) and is intended to mirror the snow-capped Rocky Mountains in the distance (Brown, 1994). This is a double-layer membrane used to improve the thermal and acoustic performance of the space (Berger, 2000, pp. 220–221). It is particularly employed to reduce the impact of aircraft engine noise on the interior. As Fig. 7.12 shows, here the distinct contrast between the bright membrane (bright, even though it is double-layer) and the duller surfaces at concourse level can clearly be seen, as discussed previously in Section 7.6.2.

In a more recent implementation of a membrane-clad envelope for the new passenger terminal at Suvarnabhumi International Airport, Bangkok, a three-layer system with overall light transmittance of 2% was used in bays (alternating with an equally high-performance glazing system) to improve thermal and acoustic performance in the hot and humid tropical climate and high-noise environment. The solution consists of a combination of cable net supported transparent 6 mm thick polycarbonate acoustic baffl es, sand-wiched between a PTFE/glass translucent exterior membrane and a lami-nated membrane incorporating a low-emissivity coated foil attached to an

(a) (b)

7.9 Glazed roof lights at Dynamic Earth, Edinburgh, to allow the penetration of direct sunlight: (a) general view; (b) roofl ight detail (photos: John Chilton).

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(a) (b)

7.11 (a) The 240 m × 193 m clear-span Georgia Dome in Atlanta, USA, completed in 1992; (b) internal cable dome support (photos: John Chilton).

(a)

(b)

7.10 (a) O2 Arena (formerly Millennium Dome), PTFE/glass fabric panels, which have only a small degree of double curvature; (b) an internal acoustic liner membrane, suspended from the net (photos: John Chilton).

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7.12 Wave form at Denver Airport – note the contrast between the bright membrane (bright, even though it is double-layer) and the duller surfaces at concourse level (photo: John Chilton).

open-weave liner (Murphy/Jahn Architects, 2006; Holst, 2006). The low-emissivity coating has the effect of blocking the radiative heat exchange between the external membrane surface and internal surfaces whilst refl ect-ing the coolness of the chilled fl oor (Holst and Schuler, 2003). Without this intervention, according to Holst and Schuler (2003) the unprotected exter-nal membrane ‘... has the same effect as a radiant ceiling heating running at a mean surface temperature of about 55°C at day peak.’

Since its high-profi le use as infl ated cushion cladding for the geodesic biomes of the Eden Project in Cornwall, ETFE has been seen by many architects as a panacea or wonder material, to such an extent that demand is tending to exceed supply. It has recently been used as cladding for both the ‘Bird’s nest’ and ‘Watercube’ stadia for the 2008 Olympics in Beijing. In the 177 × 177 × 31 metre ‘Watercube’, exterior and interior layers of cushions, with ventilated cavities between, were inserted into the space grid ‘bubble’ pattern of pentagons and hexagons to completely cover the roof and the building facades (Bosse, 2007).

Infl ated membranes may also be utilised for complete roofs, as can be seen by the cover for the Bull Ring, Centro Integrado de Vista Alegre, in Madrid, completed in 2000 (Fig. 7.13). Here a single 50 m diameter, 1960 m2, lenticular infl ated cushion, comprised of a translucent upper membrane and a lower cable net supported ETFE surface, can be raised in its entirety, by 10 m, by winching the steel ring beam up a series of perimeter columns. The opening provides ventilation and contact with the exterior environment for the spectators (Schlaich Bergermann, 2008).

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A recent engineering/architectural development is Tensairity®, where membranes are used to create infl ated beams. An infl ated tube is used both to tension resisting cables whilst also being connected to a fl exible compres-sion rib in such a way as to stabilise it against buckling. The tube, cables and rib then become mutually supporting. Considerable spans have been achieved using the minimum of material, for example in the 28 m span roof of a car parking garage in Montreux, Switzerland (EMPA, 2008). Apart from the lightweight structure which is formed, the tubes can also be illu-minated internally from the ends (taking advantage of the refl ective nature of the interior membrane surface) to create exciting lighting effects.

Textile membranes are being employed more frequently, and highly effectively, as the exterior envelope for more conventional construction, as they can provide the fl uidity and fl exibility of form that is often demanded by contemporary architecture. An interesting example is the 107 m high Air Traffi c Control Tower at Vienna Schwechat Airport. Here the conventional slip-formed concrete shaft was concealed behind PTFE/glass membranes stressed between steel frames attached to the central core. Within the 44 m height of the mid-shaft, the frames change from a square at the base to a more rounded plan at the top, while rotating through an angle of 45˚. Due to the translucency of the membrane, when illuminated internally at night it becomes a beacon to aid orientation but can also provide a massive image projection surface (Schmid, 2007).

7.7.2 Art and design

Art

The highly appealing lightweight and double-curved nature of textile sur-faces lends itself to the development of exciting and sculptural as well as

7.13 Infl ated cushion 50 m in diameter at the Bull Ring, Centro Integrado de Vista Alegre, in Madrid – a PVC/PE outer surface and an ETFE inner surface supported on cable net (photo: John Chilton).

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structural forms. These range from the public art of Jens J. Meyer (Meyer, 2008) (Fig. 7.14) and the lamps, sails and walls/screens of Gisela Stromeyer (Stromeyer, 2008) to the expansive installations of Anish Kapoor (Kapoor, 2009). His sculpture Marsyas completely fi lled the 150 metre long Turbine Hall of the Tate Modern with a burgundy-coloured PVC/PE membrane, when exhibited in 2002 (Balmond et al., 2003).

Although not strictly textiles (being fabricated from coloured PVC), the ‘luminaria’ of Architects of Air, Nottingham, UK (Architects-of-Air, 2008) demonstrate the sculptural appeal of infl ated forms. In this case the instal-lations may be experienced in a different way, from the outside as is more usual, but also more intensely on the inside, where one may encounter the full impact of the strong colours used in the surface envelope (Figs 7.15 (a) and (b)).

Exhibition stands

The minimal weight, fl exibility and portability of textile structures makes them ideally suited for use in exhibition and trade fair stands (Fig.7.16). According to the material manufacturer Ferrari (2009), the advantages of interior textile architecture are:

• Lightness, fl exibility and strength• Adaptability to large free spans, curved shapes and irregular surfaces• Light diffusion and refl ection; acoustic absorption

7.14 Tensile fabric sculpture by Jens J. Meyer exhibited at Techtextil 2009 (photo: John Chilton).

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(a) (b)

7.15 Sculptural interior of ‘luminaria’ by Architects-of-Air, Nottingham (photos: John Chilton).

• Resistance to humidity• Available colour range and the acceptance of graphics.

Acoustic and light refl ectors/diffusers

Although, as noted in Section 7.6.3, tensioned membranes have only limited acoustic insulation properties, they may be used as an aesthetically pleasing way to control the internal acoustic environment as absorbers and refl ec-tors. However, more commonly, textiles are very effectively utilised as light refl ectors/diffusers, as can be seen at Terminal 4, Barajas Airport, Madrid, opened in 2006. Here two types of refl ector/diffuser are used to maximise ingress of daylight, whilst avoiding glare and overheating from direct sun-light, and to minimise lighting and cooling energy consumption. At the high level, lenticular modules comprised of ETFE foil (with 95% translucency) on the outer face and silicone-coated glass fabric (with 45% translucency) on the inner surface form 5 m diameter diffusers under circular skylights (Anon, 2004) (Fig. 7.17). At the lower level, a set of cigar-shaped elements

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7.16 TensiNet competition exhibition stand at Techtextil 2009 (photo: John Chilton).

7.17 High-level fabric diffuser at Terminal 4, Barajas Airport, Madrid (photo: John Chilton).

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covered on both sides by silicone-coated glass fabric act as combined dif-fuser/refl ectors (Figs 7.18 (a) and (b)).

7.8 Future trends

Within the scope of this chapter it is not possible to describe in detail the wide range of developments that are happening with textiles used for tensile structures in architecture and design. However, the following paragraphs give a taste of the potential of what is a structural/architectural material still in its infancy.

New coating materials are being explored. For example, Mehler Texnologies GmbH have recently introduced Valmex® vivax, a THV-coated polyester material (Mehler Texnologies, 2009). The THV coating,

(a)

(b)

7.18 Low-level diffuser/refl ectors at Terminal 4, Barajas Airport, Madrid (photos: John Chilton).

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which is a blend of tetrafl uoroethylene, hexafl uoropropylene and vinyli-dene fl uoride, has a lower processing temperature than the PTFE used in PTFE/glass fabrics. The material is described as having high resistance to weathering and ageing, good dirt-repelling properties, high-frequency weldability, and fl exibility, the last of these reducing the risk of damage when folded.

Due to ever more stringent constraints on energy consumption in build-ings, for roofs and facades the trend is towards the development of more energy effi cient envelopes. Where the loss of translucency is not an issue some fabricators are experimenting with the incorporation of multi-foil insulation products. In this area, a recent innovation by Birdair is their product TensothermTM, which consists of a 9 mm thick sandwich of Nanogel® between two surfaces of PTFE-coated fabric (Birdair, 2008). The fi rst appli-cation of this product was in the refi t/upgrade of an existing membrane roof at Dedmon Athletic Center, Radford University, Radford, VA, USA, early in 2009 (Mak Max, 2009a).

The presentation of FTL Design Engineering Studio’s tensile fabric roof with integrated photovoltaic panels at the Cooper-Hewitt National Design Museum in 1998 opened the eyes of architects and engineers to the possibility of mass production of electrical power at the point of use through photovoltaic textile roofs (FTL Design Studio, 2009). Since then there have been considerable developments in new materials, for example Konarka’s patented Power Plastic® fl exible organic photovoltaic material, which is 0.05–0.25 mm thick, semi-transparent and printable (Amon, 2009).

Biomimetic textiles are under development and these include hydropho-bic, self-cleaning surfaces analogous to the behaviour of leaf surfaces occur-ring in nature, such as the lotus plant, and fl exible, translucent thermal insulated membranes analogous to the behaviour of the polar bear’s fur (Stegmaier and Planck, 2007).

In the area of interior architecture the properties of available fabrics and the diversity of their application are expanding rapidly. For example, prod-ucts such as ETTLIN lux (ETTLIN, 2009) create fascinating optical effects when back-lit, as a result of its tailor-made weave properties; fl exible, tem-perature-sensitive, colour-changing fi lms such as ChroMyx™ by Chameleon International (2009) can be laminated onto a variety of fabrics for yet unforeseen purposes.

Photocatalytic membranes incorporating titanium dioxide (TiO2) improve the self-cleaning performance and reduce streaking of tensile surface struc-tures. In the case of PTFE TiO2 coated membranes, the surface has also been proven to remove exhaust pollutants from the atmosphere, effectively cleaning pollution from the urban environment (Mak Max, 2009b).

As the conservation of material and energy resources and the reduction of carbon gas emissions become more imperative, the ability to recycle

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textile roofs grows ever more important. To this end some recycling pro-cesses have already been developed, for example Texyloop/Vinyloop, which converts PVC/PE fabrics into their constituent components – PVC pellets and a polyester wool (http://www.vinyloop.com).


A key source of further information on textile structures is the TensiNet Association, based in Brussels (TensiNet, 2008), which published the European Design Guide for Tensile Surface Structures (Forster and Mollaert, 2004) and also publishes a twice-yearly newsletter, TensiNews. Its website has a comprehensive database of projects, companies, literature (including some past copies of TensiNews), links to other websites and a calendar of events relevant to the fi eld of tensile surface structures. The TensiNet Association has several Working Groups, for example on Analysis and Materials, Specifi cation and ETFE, and also organises symposia including events in Brussels (2003), Milan (2007) and Sofi a, Bulgaria (2010), for which published proceedings are available (Mollaert et al., 2003; Bögner-Balz and Zanelli, 2007). In the USA, an equivalent organisation is the Industrial Fabrics Association International (IFAI) (http://www.ifai.com), which publishes Fabric Architecture (http://www.fabricarchitecturemag.com) (accessed 20/7/2010).

A comprehensive list of material manufacturers and coaters, fabricators and software can be found on the TensiNet Association website, and the research consortium Contex-T also presents an extensive list of contacts on its web pages (http://contex-t.ditf-denkendorf.de/index.php). A selection of information sources are listed below:

Material manufacturers

Ferrari http://www.ferrari-textiles.com/ or http://www.ferrari-architecture.com/ (accessed 20/7/2010)

Gore http://www.gore.com/ (accessed 20/7/2010)Mehler-Haku http://www.mehler-texnologies.com/ (accessed 20/7/2010)Taconic http://www.taconic-afd.com/ (accessed 20/7/2010)

Fabricators

Architen Landrell Associates http://www.architen.com/ (accessed 20/7/2010)Birdair http://www.birdair.com/ (accessed 20/7/2010)Canobbio http://www.canobbio.com/ (accessed 20/7/2010)Ceno-Tec http://www.sattler-europe.com/sattler-web/ (accessed 20/7/2010)Tentech http://www.tentech.nl/ (accessed 20/7/2010)

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Designers

SL Rasch GmbH http://www.sl-rasch.de/ (accessed 20/7/2010)Hopkins http://www.hopkins.co.uk/ (accessed 20/7/2010)Buro Happold http://www.burohappold.com/Arup http://www.arup.com/Schlaich Bergermann und Partners http://www.sbp.de/ (accessed 20/7/2010)Form-TL http://www.form-tl.de/ (accessed 20/7/2010)Tensys Ltd http://www.tensys.com

Art and design

Anish Kapoor http://www.anishkapoor.com (accessed 20/7/2010)Architects-of-Air http://www.architects-of-air.com (accessed 20/7/2010)Jens J. Meyer http://www.jj-meyer.de/en/ (accessed 20/7/2010)Gisela Stromeyer http://www.stromeyerdesign.com/ (accessed 20/7/2010)

Formfi nding software

Formfi nder http://www.formfi nder.at/ (accessed 20/7/2010)Forten http://www.forten32.com/ (accessed 20/7/2010)Kurvenbau http://www.kurvenbau.com/ (accessed 20/7/2010)TechNet (Easy) http://www.technet-gmbh.com/ (accessed 20/7/2010)

Flexible photovoltaics

Flexcell http://www.fl excell.com/ (accessed 20/7/2010)Konarka http://www.konarka.com/ (accessed 20/7/2010)Plextronics Inc. http://www.plextronics.com/ (accessed 20/7/2010)PowerFilm Inc. http://www.powerfi lmsolar.com/ (accessed 20/7/2010)Silicon Genesis http://www.sigen.net/ (accessed 20/7/2010)United Solar Ovanic http://www.uni-solar.com/ (accessed 20/7/2010)

7.10 References

Amon A (2009), ‘The ephemeralization of energy production: Photovoltaics using fabric’, Fabric Architecture, 21(3), 26–30

Anon (2004), ‘Skylight diffusers Madrid-Barajas new airport terminal’, TensiNews 6, Brussels, TensiNet, 6–7

Architects-of-Air (2008), http://www.architects-of-air.com (accessed 20/7/2010)Balmond C, Carroll C, Forster B and Simmonds T (2003), ‘Engineering Marsyas at

Tate Modern’, The Arup Journal, 38(1), 40–45

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Barnes M and Dickson M (2000), Widespan Roof Structures, London, Thomas Telford

Berger H (1996), Light Structures, Structures of Light, Berlin, BirkhäuserBerger H (2000), ‘Engineering an integrated architecture for wide span enclosures’,

in Barnes M and Dickson M, Widespan Roof Structures, London, Thomas Telford, 220–221

Birdair (2008), http://www.birdair.com/tensileArchitecture/tensotherm.aspx (accessed 20/7/2010)

Bögner-Balz H and Zanelli A (2007), Ephemeral Architecture: Time and Textiles, Milan, Libreria CLUP

Bosse C (2007), ‘ “Watercube” – National Swimming Centre in Beijing’, Detail (12), 1469–1475

Bradatsch J, Pätzold P, Saboia de Freitas C, Scheuermann R, Monjo J and Mollaert M, ‘Form’, in Forster B and Mollaert M (2004), European Design Guide for Tensile Surface Structures, Brussels, TensiNet, 44–82

Brown ML (1994), ‘Denver International Airport tensile roof case study: the fabrica-tion and construction process’, in Abel JF, Leonard JW and Penalba CU, Spatial Lattice and Tension Structures, New York, ASCE, 969–978

Campioli A, Mangiarotti A and Zanelli A (2007), ‘Learning from the past to renew ephemeral architecture in the Italian context’, in Bögner-Balz H and Zanelli A, Ephemeral Architecture: Time and Textiles, Milan, Libreria CLUP, 187–201

Chameleon International (2009), http://www.chameleonint.com/ (accessed 20/7/2010)

Chilton JC, Blum R, Devulder T and Rutherford P (2004), ‘Internal environment’, in Forster B and Mollaert M, European Design Guide for Tensile Surface Structures, Brussels, TensiNet, 97–146

Devulder T, Wilson R and Chilton JC (2007a), ‘The thermal behaviour of buildings incorporating single skin tensile membrane structures’, International Journal of Low-Carbon Technologies, 2(2), 195–213

Devulder T, Chilton J, Wilson R and Blum R (2007b), ‘Advanced textile skins: pre-dicting the thermal response of complex membrane constructions’, in Bögner-Balz H and Zanelli A, Ephemeral Architecture: Time and Textiles, Milan, Libreria CLUP, 61–74

Drew P (1976), Frei Otto, Form and Structure, London, Crosby Lockwood StaplesEMPA (2008), http://www.empa.ch/css (accessed 20/7/2010)ETTLIN Spinnerei und Weberei Produktions GmbH (2009), http://www.ettlin.de/

de/content/neuelinie.html (accessed 20/7/2010)Ferrari (2009), http://www.ferrari-architecture.com/ (accessed 20/7/2010)Forster B and Mollaert M (2004), European Design Guide for Tensile Surface

Structures, Brussels, TensiNetFTL Design Studio (2009), ‘Under the sun’, http://www.ftlstudio.com/ (accessed

20/7/2010)Gore (2009), http://www.gore.com/en_xx/products/fabrics/architectural/gore_tenara

_architectural_fabric_woven.html (accessed 20/7/2010)Holst S (2006), ‘Suvarnabhumi International Airport Bangkok – Innovative Climate

Concept’, Detail (7+8), 820–822Holst S and Schuler M (2003), ‘Innovative energy concept for the new Bangkok

Airport’, in Mollaert M, Haase J, Chilton JC, Moncrieff E, Dencher M and Barnes M, Designing Tensile Architecture, Brussels, TensiNet, 150–167

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Hopkins Architects (2008a), http://www.hopkins.co.uk/projects/_4,13/ (accessed 20/7/2010)

Hopkins Architects (2008b), http://www.hopkins.co.uk/projects/_1,75/ (accessed 20/7/2010)

Houtmann R and Werkman H (2004), ‘Detailing and connections’, in Forster B and Mollaert M, European Design Guide for Tensile Surface Structures, Brussels, TensiNet, 148–175

Huntington CG (2004), The Tensioned Fabric Roof, New York, ASCE, 66–78Kapoor A (2009), http://www.anishkapoor.com/works/gallery/index.htmKoch K-M (2004), Membrane Structures, Munich, PrestelLiddell I (2000), ‘The construction of the Millennium Dome, London’, Detail (6),

1040–1043Mak Max (2009a), http://www.makmax.com/news/2009/nw0601.html (accessed

20/7/2010)Mak Max (2009b), http://www.makmax.com/business/tio2.html (accessed 20/7/2010)Mehler Texnologies (2009), Data sheet V038/06/2009 ‘Valmex® vivax, The innova-

tive fl uorothermoplastic coated material for permanent tensile structures’, Mehler Texnologies GmbH, D-41836 Hückelhoven, Germany

Meyer JJ (2008), http://www.jj-meyer.de/en/ (accessed 20/7/2010)Mollaert M, Haase J, Chilton JC, Moncrieff E, Dencher M and Barnes M (2003),

Designing Tensile Architecture, Brussels, TensiNetMurphy/Jahn Architects (2006), ‘Passenger Terminal Complex Suvarnabhumi

International Airport Bangkok’, Detail (7+8), 810–814Nerdinger W, ed (2005), Frei Otto Complete Works: Lightweight Construction Natural

Design, Basel, BirkhäuserOtto F and Rasch B (1995), in Schanz S, Finding Form: Towards an Architecture of

the Minimal, Fellbach, Axel MengesPudenz J (2004), ‘Materials and workmanship’, in Koch K-M, Membrane Structures,

Munich, Prestel, 48–65Scheuermann R and Boxer K (1996), Tensile Architecture in the Urban Context,

Oxford, Butterworth ArchitectureSchlaich Bergermann und Partner (2008), ‘Roof for bullfi ght arena – Vista Alegre’,

http://www.sbp.de/en/fl a/mittig.html (accessed 20/7/2010)Schmid G (2007), ‘Membrane cladded air traffi c control tower, Vienna: Job report’,

in Bögner-Balz H and Zanelli A, Ephemeral Architecture: Time and Textiles, Milan, Libreria CLUP, 217–226

Stegmaier T and Planck H (2007), ‘Textile material development for textile con-struction’, in Bögner-Balz H and Zanelli A, Ephemeral Architecture: Time and Textiles, Milan, Libreria CLUP, 99–104

Stromeyer G (2008), http://www.stromeyerdesign.com/ (accessed 20/7/2010)TensiNet (2008), http://www.tensinet.com (accessed 20/7/2010)Terry WR (1994), ‘Georgia Dome cable roof construction techniques’, in Abel JF,

Leonard JW and Penalba CU, Spatial Lattice and Tension Structures, New York, ASCE, 563–572

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258

8The role, properties and applications of textile

materials in sustainable buildings

J. POHL, Lightweight Constructions Institute, Germany and G. POHL, Saarland University of Applied Sciences, Germany

Abstract: Textile buildings play an emerging role when focusing on buildings that use or consume as few resources as possible, concerning energy needs as well as material use. This chapter deals with the role of textile materials in sustainable buildings, applications and properties of textiles used for roofi ng and facades of sustainable building concepts. As an example of a so-called greenhouse concept, the functionality and material properties of the membrane facade of Terminal EF in Erfurt, Germany, are described in detail.

Key words: greenhouse concept, sustainable building concept, membrane facade, PTFE glass facade, PTFE coated glass mesh, textile building, textile materials in sustainable buildings, textile facade, membrane building, high performance facade, high tech facade, innovative building concept, innovative facade concept, textiles in architecture.

8.1 Introduction

Nowadays, discussions on architecture, apart from the aspects of pure design, centre on themes of effectiveness – such as usability by quality of use, changeability and cost-effi ciency. The more we study publications by the users of our buildings and magazines on architecture, the more we notice that energy effi ciency is among the most important themes and is mostly connected with demands on effi ciency.

A great percentage of the energy consumed all over the world is used to run buildings. In Switzerland, space and water heating in residential buildings account for one quarter of the overall Swiss energy consumption (see Kost, 2006), while a further 25% is accounted for by traffi c, as it is in most European countries. In Belgium, the CO2 emissions from heating buildings increased by 11.6% between 1990 and 2005 and, at the same time, the CO2 emissions for transport increased by 27.5%. The overall percentage of CO2 emissions from heating buildings is around 22% and for transport it is calculated to be 18.4% (Hubert, 2008). Large quantities of fossil fuel are used to generate the energy needed to maintain our standard of living.

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The role, properties and applications of textile materials 259


In addition to this, the intensive cultivation of plants for renewable energy competes with the land needed for heating or cooling our buildings and for transportation. Vast areas of rainforest are being destroyed for this purpose, and the worldwide reduction in the areas of land devoted to agriculture is leading to a progressive diminution of natural habitats and an increase of CO2 in our atmosphere. Global warming is no longer a question for discussion; it is seen as a fact by nearly all the experts, whilst the reason behind it can be seen in people’s way of living.

This situation calls for a rapid and fundamental reorientation in our thinking, particularly towards the structure of our built environment. In the future, architects must exert a far more decisive infl uence on the plans for urban structures, building concepts and constructive components, to achieve a reduction in the use of energy for producing buildings and their lifetime energy consumption.

8.2 The role of textile materials in

sustainable buildings

Beside the subjects of energy consumption and CO2 footprint, there are other important reasons for sustainability. The use of architecture with regard to its social components is one of the most important when thinking about lifetime usability. Architecture means building space. Architecture has long durability, therefore it is not easy to change or move. We can see in environments with social problems that the architecture also looks similar to these problems. If one is confronted with rigid, brutal architecture, for example in sports stadiums, this will cause the same brutal feelings in people towards their neighbours. If buildings are in a poor state of repair, no one will care about damage or pollution. So, both the material aspect and the design aspect are essential for solving the demands on social archi-tecture. Within this, demands on social architecture that are both energy-effi cient and cost-effi cient need examining as joint demands on sustainable architecture. In the design of buildings, materiality is considered to be one of the major ways to achieve these multipurpose requirements.

Textile architecture plays a growing role in these considerations. Textile architecture helps to give a friendlier aspect to the more rigid materials of buildings. Constructions made of textiles are light, mostly able to let the sun pass through, and give the feeling of sunlight. Textiles are used for several purposes, the main ones being in constructions and buildings as protection from the sun and rain since they are used for roofs and walls. Textiles can protect from the sun as well as let certain amounts of sun pass through to illuminate the interior with daylight. They can be used for insula-tion against heat or noise if they are constructed of elements with more than a single layer, and can be used for parts of buildings – roofs, facades

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or interior parts – as well being the main material of which the buildings are made.

However, textile buildings are very important for our urban and archi-tectural environment. The examples that have been designed during the last few decades have been mostly positive. There are many long-term studies on durability which can make these relatively new materials inter-esting for emerging markets.

The following examples are only able to give a pointer to forward-looking solutions. They should show the interesting improvements our building technology can make towards achieving sustainability by means of social functionality and by the use of textile materials.

8.3 Applications and properties of textiles used

for roofi ng and facades of sustainable

building concepts

8.3.1 Early examples and principles

Sustainable buildings have to save our environmental resources. By means of sustainability, the target is not only to minimize the use of energy and materials or to optimize the consumption of renewable energy rather than using oil-based products, but to optimize architectural objects in terms of the quality of space: the feeling of working and living in daylight includes the social demands discussed above.

An early example was the design of a city in the Antarctic, which was published in 1971 by Kenzo Tange, Ted Happold, Ove Arup and Frei Otto (Figs 8.1 and 8.2), where 45,000 people could live. Polyester ropes would span 2000 m in the form of a shell structure and carry a two-layer envelope of synthetic material.

8.1 External view of city in the Antarctic by Kenzo Tange, Ted Happold, Ove Arup and Frei Otto, 1971 (Source: Frei Otto, Warmbronn, Germany).

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8.2 Internal view of city in the Antarctic by Kenzo Tange, Ted Happold, Ove Arup and Frei Otto, 1971 (Source: Frei Otto, Warmbronn, Germany).

8.3 58 Degrees North by Kenzo Tange, Ted Happold, Ove Arup and Frei Otto (Source: Frei Otto, Warmbronn, Germany).

In this period, many famous architects and civil engineers carried out futuristic projects (Fig. 8.3), enveloping smaller cities or even a whole part of Manhattan, like Richard Buckminster Fullers’ design (Fig. 8.4).

The US pavilion at Expo 1970 in Osaka, constructed by Birdair (Figs 8.5 and 8.6), was a 262 foot × 460 foot cable dome. Vinyl-coated fi breglass fabric was used to span between steel cables, which varied in thickness from 1½ to 2¼ inches (Fig. 8.7). The volume was supported by internal pressure.

Wide-span buildings using textile material were of less interest in the 1980s. While most architects and engineers were looking to produce con-structions in concrete, there were still some projects, like the 1982 Hubert M. Humphrey Metrodome in Minneapolis, which were constructed using Tefl on-coated fi breglass. The inner pressure that was necessary to stabilize the form made it necessary to use airlocks, which was not a perfect situation

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8.4 Dome over Manhattan by Richard Buckminster Fuller.

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in terms of usability and fl exibility for certain events. Questions about the durability of the material and construction problems also led to most of these projects coming to an end. Later, the projects scaled down their ele-ments and combined primary supporting constructions with the assembling of the envelope.

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8.6 Aerial view of US pavilion Cable Dome at Expo in Osaka, constructed by Birdair, 1970.

8.7 Internal view of US pavilion Cable Dome at Expo in Osaka, constructed by Birdair, 1970.

In 1989–1991, Philippe Samyn constructed the M&G research laboratory in Venafro, Italy (Fig. 8.8). The roof structure used a membrane, under which the research areas were placed in a similar manner to the early Antarctic city of Tange, Happold, Arup and Otto. The measurements were 35 × 85 m. Six curved-steel framework arches supported the membrane made of PVC-polyester, which had a span of 12–15 m. The interior was ventilated mechanically using propulsion and suction ventilators at the tent’s extremities. An independent air-conditioning system was installed in the box-like offi ces and laboratories.

In 1990, Göran Pohl, when a young architect, designed his fi rst project using a membrane to cover a large space for an event arena based in

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Stuttgart, Germany (Fig. 8.9). Studies of the construction of the Munich swimming centre (Fig. 8.10), built by Günther Behnisch in 1972, and studies of other big constructions, among them the covered ice arena of Kurt Ackermann (Fig. 8.11) next to Behnisch’s Olympic buildings, constructed in the late 1980s, inspired his detailed solutions of the roofi ng. He devel-oped a 150 × 250 m span multipurpose sports hall, but compared to Ackermann’s hall, using 10 backbone-like beams as primary constructions (Figs 8.11 and 8.12) and a further development of the roof construction of the Olympic Swimming Hall of Munich: multi-layer membranes with high

8.8 M&G research laboratory in Venafro, Italy by Philippe Samyn, 1991.

8.9 Design for an unbuilt event arena covering a tennis centre court including a stage for 10,000 spectators and two tennis courts for 2000 spectators each in Stuttgart, Germany, 1990.

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8.10 Munich Swimming Centre, Germany by Behnisch, 1972.

8.11 Munich Ice Arena, Germany by Kurt Ackermann, 1983.

translucency were designed to fulfi l insulation demands as well as the need for bright light.

To prevent overheating, the covering could be ventilated naturally by using the physical effects of the Bernoulli fl ow and also by means of an air-conditioning system within the envelope. The inner membrane was

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PTFE (polytetrafl uoroethylene) laminated glass mesh, a newly developed material combination which Friedemann Kugel, at Stromeyer Ingenieurbau, and the team of Frei Otto at the IL – Institute of Lightweight Structures – in Stuttgart, had been discussing in depth with Göran Pohl. Stromeyer Ingenieurbau was already doing research for countries in the Middle East into a laminated mesh material using PTFE foils as a coating for a fabric with a wide mesh. At this time, the well-known PVC-coated polyester membranes would have had a translucence degree of around 10% or even less in one layer, which would have added less than 1% translucency, depending on the type of material used for tension strength and thickness. The material to be used for the design had to carry tension loads similar to type 2 and achieve a minimum translucency of 50%. The multi-layer con-struction was designed to support an overall translucency of around 25%. Compared to the Olympic swimming arena in Munich, where the insulation between the membranes had no translucency, the open-air feeling under the insulated construction of the Stuttgart arena was calculated to offer a well-conditioned climate for the visitors, which was thought to be the great advantage of membrane buildings. Göran Pohl detailed the outer skin with plates of polycarbonate (Fig. 8.13).

The cleverness of this construction was that, compared to other construc-tions at this time and the early big arenas or city envelopes, it could use solar energy and – with the same construction – prevent overheating and offer a large insulated space with an open-air feeling for up to 20,000 people. In 1992, in the programme for the international design competition that the city of Berlin launched to offer a swimming and cycling arena for the candidature of the 2000 summer Olympic Games, Göran Pohl and his team were mentioned for their design of two arenas, a swimming and cycling arena enhancing his ideas of insulated climate envelopes supported by space frame arches in the manner of steel backbones (Fig. 8.14).

To fulfi l the demands of insulated membrane buildings in the future, research had to make more progress. In the late 1990s, the industry princi-pally offered two different possibilities for building insulated roofs and walls: buildings using cushions, mostly made of ETFE, or buildings with textile membranes, mostly made of PVC-coated polyester. Fibreglass mesh

8.12 Side view of the event arena in Stuttgart, Germany by Göran Pohl, 1990.

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laminated with PTFE was a new material just on the market and at fi rst it was only used for single-layer constructions in buildings. The cultural centre of Puchheim, Germany, designed by Peter Lanz, was one of the fi rst to be enveloped in a multi-layer construction of PTFE-coated glass fabric.

Materials and light transmission

Membrane constructions do not usually provide any insulation. Multi-layer membranes are combined with insulation material, which is typically used to insulate large walls and traditional roofs. In the late 1990s, the industry began to support materials that could be combined to provide insulated and highly translucent roofs or walls. When spun glass in the form of cush-ions is used for the insulation material, about 50% of the light can pass through it. Even with the PTFE-glass fi bre fabric on the top and bottom edges, the transmission will still be around 10–15% where the light is scat-tered by the spun material. The construction offers daylight with a moder-ate temperature increase during sunny hours. On clear sunny days, about 200 W/m² will pass through. The intensity of light is around 20,000 lux at noon (in comparison, 300 to 500 lux are required in offi ces). Even on cloudy days, the illumination is about 2000 lux. On cold nights, the insulation prevents heat radiating out and thereby prevents extreme cooling. One example is given by the material combination of PTFE-coated glass mesh, offered by Flontex, a small company in Blaustein, Germany: Table 8.1 shows elements of the multi-layer construction, and Table 8.2 lists thermo-physical characteristics of the combined construction.

8.14 International design competition: swimming and cycling arena in Berlin by Göran Pohl, 1992.

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Table 8.1 Elements of the multi-layer construction offered by Flontex

Layer Material Degree of transmission

1 PTFE-glass lattice fabric 54%2 Glass fi bre tissue 55%3 PTFE-glass lattice fabric 54%

Table 8.2 Thermophysical characteristics of the combined construction offered by Flontex

Heat exchange coeffi cient u = 1,1 W/m²KTotal degree of energy permeability g = 26%Degree of transmission te = 20%Degree of refl ection re = 43%Degree of light transmission L = 22%

Since 2000, there have been many well-documented projects using cushions of ETFE, although the early projects reported loss of air and detailing problems. The multi-layer membrane projects using fabrics like PTFE glass mesh seemed to be safer constructions because they did not lose air and did not need any additional equipment running all the time to replace the air lost by details and materials.

Meanwhile, new companies have been doing further research and now offer advanced materials. Very thin, spun-glass fi bres that are fi xed with a UV-stable fi xator and spun into a lightweight, highly translucent tissue are now being developed by the company Wacotech. The air encapsulated between the glass-fi bre ‘hairs’ gives the material very good insulation prop-erties. The spun glass fi bres offer an extreme diffusion of light, which is very muted and causes almost no dazzle compared with direct light trans-mittance through glass. In summer, they provides good protection from the sun, helping to prevent overheating, and producing a low g-value. The spun glass fi bre can be added to more than one layer, depending on the u-value and light transmittance. Spun glass-fi bre tissue is produced in standard thicknesses of 70 mm. The length is up to 6000 mm and the width is 1000 mm (TI Max GL, Wacotech). Other dimensions may possibly be produced – see Table 8.3.

Projects using the new combinations of membrane and spun fi bre tissue are, for example, the building of the research centre in Erfurt, Terminal EF, in Germany. The construction of Terminal EF has been mentioned by a research project that is monitoring long-term usability for the European Union programme of SolarBau Monitor. In the following section, this building is used as an example of how membrane constructions could be carried out for sustainable buildings.

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8.15 Terminal EF in Erfurt, Germany by Pohl Architekten.

Table 8.3 Glass fi bre insulation material

Product Wacotech TI Max GL/SMaterial Glass fi breColour White/translucentUsability temperature range (°C) −30 to +120Burn-proof B1 certifi ed, A2 orientedDegree of transmission 0.48Heat coeffi cient (W/m2K) 1.45

8.3.2 Terminal EF – an innovative facade construction with textile membranes (Fig. 8.15)

Overview

The western facade in the TMZ Erfurt is supported by a steel construction of arched steel girders and compression struts. These arched girders, as HEA 240 steel girders, were manufactured based on a certain geometry and static analysis guided by the functionality of the membrane. The cal-culated arched geometry of the steel girder constituted the basis for the membrane design and membrane shape. The overall width of the mem-brane fi elds is 5.0 m. The cyclic change between the membrane and glass fi elds was found after extensive simulation and calculation of lighting effects. Each 5 m wide membrane fi eld is followed by a 2.5 m wide glass fi eld.

The membrane construction has an anticlastic curvature and is mechani-cally pre-stressed. The overall construction comprises three layers. The

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inside membrane is made of PTFE-laminated fi breglass cloth followed by a 10 cm thermal insulation cushion of fi breglass matting. The outer membrane of PTFE-laminated fi breglass cloth is placed above a 20 cm thick air cushion. This construction is attached to the substructure at the edges by means of fastening systems at specifi c points. The membrane fi elds are linearly supported on three sides. The top termination is formed by a steel rope threaded through a membrane pocket.

Technically, the membrane fi elds are considered to be structures that need no static load-bearing function. Failure of the inner or outer membranes cannot damage the structure or cause injury to people. Horizontal bracing was applied to create uniform loading conditions throughout: this was to cater for theoretical causes of damage, such as strong winds, and also times when individual fi elds needed to be replaced or repaired. This created a high margin of safety to ensure that the distribution of forces, which may initially cause high load peaks in the region of the glass fi elds, remains uniform under all possible loading conditions. In this way, virtually all the relevant scenarios for damage could be excluded.

Specifi c challenges of Terminal EF

The challenges of this specifi c project were to form membranes from textile building materials and to develop functions specifi cally for use in facade constructions in intelligent, complex and layered systems.

Membrane materials were used fi rstly for the outer facade on the north-west side of Terminal EF, shown in (Fig. 8.15), and secondly as a covering construction for the connection bridges between parts of the building (Fig. 8.16). The building system offers a very accurate programme for reducing energy consumption and fulfi ls all current greenhouse stan-dards, as certifi cated by the European research programme ‘SolarBau Monitor’.

In order to explain the system of using textiles for sustainable building concepts in detail, the calculations and assumptions need to be shown. The membrane facade of Terminal EF is mechanically pre-stressed and anticlastically curved in three dimensions (Fig. 8.17). The double-walled membrane is made up of one outer membrane, one inner membrane and one intermediate insulating layer. The insulation layer is fi xed to the inner membrane, which runs parallel to the outer membrane (Fig. 8.18). Within the determined geometric frame, the side edge runs along a curved steel HEA 240 beam, the upper edge comprises an arched 10 mm to 14 mm inner steel rope, and the bottom edge runs straight along the steel beam. The membrane tension is created by the geometry and by pre-stressing in the direction of the arched girders.

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8.16 Connecting bridges between the separated buildings of Terminal EF in Erfurt, Germany, glowing by night, by Pohl Architekten.

8.17 Internal view of Terminal EF showing the membrane facade in Erfurt, Germany by Pohl Architekten.

Theoretical calculations, load bearings, physical behaviour and material properties

The static calculations for Terminal EF are based on membrane theory, with the following load assumptions:

• Material weight 0.02 kN/m2

• Pre-stress: two-axial pre-stressing to protect the membrane against fl apping and tearing. In addition, pre-stressing prevents wind-induced

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oscillation. In this way, the membrane dampens oscillations in the entire structure. Loading reduces the pre-stress. Loading by snow and wind is therefore not superimposed on loading by pre-stressing.

• Applied pre-stress: v = 2.00 kN/m• Wind load: height above ground 18.5 m, wind pressure 0.8 kN/m2

• Pressure coeffi cients for wind-parallel exterior walls 18.50/62.25 = 0.30; calculated 0.70

• Snow load zone 2 → 0.75 kN/m2.

The calculated loads for the supporting structures of the membrane areas are:

• Load case for edge ropes: Nmax 30.15 kN• Load case, wind pressure: edge rope tension-force max. 26.7 kN• Load case, negative wind pressure + pre-stress: edge rope tension-force

max. 55.1 kN• Calculated rope diameter 14/1 × 37 DIN 3054, min. breaking load

167.7 kN (weight 0.958 kg/m, diameter ds = 14 mm), 0.85 × 167.7 kN/55.1 kN = 2.59 > 2.2.

The results for the supporting structures are:

• Outer membrane fi elds: rope 14 mm, DIN 3054, 1 × 37, thread fi ttings type 969 Pfeiffer, size 140

8.18 Layers and installation of the membrane facade at Terminal EF in Erfurt, Germany by Pohl Architekten.

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• Inner membrane fi elds: rope 10 mm, DIN 3054, 1 × 37, thread fi ttings type 968 Pfeiffer, size 100

• Outer membrane of PTFE-coated glass fabric, Type II• Short-time tear strength N = 100 kN/m• Max. membrane loading occurs in load case snow + wind pressure:

12.70 kN/m• Due to manufacturing tolerances, a reduction by 15% is calculated:

reduction factor 0.85• After ageing, material and manufacturing data as well as installation

tolerances, an overall reduction of ages = 3.00 is assumed• The safety factor is summarized as follows: ν = 100/(3.00 × 12.70) × 0.85

= 2.23 > 1.3erf.

Tests and assumptions

The strength tests were carried out at Laboratorium Blum, Stuttgart, Germany and gave the following results:

• The strength of the test strips was 48.0 kN/m at 20°C and 40.0 kN/m at 70°C.

• To calculate the strength after 20 years, it is assumed that the strength curve is exponential. A strength of 32 kN/m was calculated after 20 years.

• The safety factor with respect to the maximum load tension of 11 kN/m, after 20 years at 20°C, is calculated as 32/11 = 2.90 minimum.

• The theoretical safety factor with respect to the maximum load tension of 11 kN/m, after 20 years at 70°C, is calculated as 30/11 = 2.72 minimum.

According to tests at Laboratorium Blum, the short-time tear strength is not the determining factor for material strength, but rather the strength of the edge attachment. The calculated working stresses were found to be 12.7 kN/m in the warp direction and 11 kN/m in the weft direction. A minimum safety factor of s = 6 should be guaranteed. This then yields 76 kN/m and 66 kN/m in the warp and weft directions respectively. These results were exceeded after testing, i.e. the safety factors were higher.

The ultimate failure loads for the clamps are higher than the ultimate stress for the seam. Therefore, the strength of the seam determines the overall strength.

Young’s modulus (source: Laboratorium Blum)

By linear approximation, the relationships for an orthotropic elastic mate-rial between elongations ek and es and for stresses nk and ns in the warp and weft directions respectively are given by:

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nk = Ekkek + Ekses

ns = Eksek + Esses

Ekk and Ess are the stiffnesses in the warp and weft directions respectively and Eks represents the infl uence of transverse elongation. The effect of transverse elongation may be ignored, however, due to negligible inter-action between the warp and weft directions.

Ekk = 3065 kN/m

Eks = 2030 kN/m

Inner membrane

The inner membrane is loaded only by pre-stressing. There are no other stress conditions, which obviates the need for the strength calculations. In addition, the membrane is irrelevant with respect to safety since the safety of the structure would not be affected should the membrane fail. Table 8.4 shows the membrane characteristics overview of the outer membrane and the inner membrane facade of Terminal EF.

Glass-fi bre insulation material

The distance between the inner membrane and the outer membrane is 300 mm. Inside this is fi xed a 100 mm cushion of spun insulation material, which is made from fi breglass spun matting. The technical data are as follows:

• Fibreglass spun matting: 100 mm, dyed white, 3 g/m2, comprising oxides, silicone, aluminium, calcium, boron and magnesium (8 IIR TWA)

• Surface binding agent: urea-formaldehyde resin, 2.5 mg/m3. Low bleach-ing agent content (8HR TWA formaldehyde)

• Softening point: 670–720°C• White, refracting, spun glass fi bres, glass fi bre diameter 20–30 μm• Total specifi c area weight 346 g/m2, fi breglass matting covered with

unprocessed glass fabric.

The insulating cushion is fi xed on the inner membrane and additionally hooked laterally into the eyelets on the arched girder. The surface is held in place by means of Velcro tape attached to the welding seams.

Table 8.5 gives a physical product assessment of the complex construc-tion described above.

The heat exchange coeffi cient of the entire structure is 1.1 W/m2K, the total energy permeability factor is 17%, the transmission factor is 6%, the degree of refl ection 34% and the light transmission factor 22% (source:

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Table 8.4 Membrane characteristics overview of the outer membrane and the inner membrane facade of Terminal EF

Outer membrane (F 4683/220)

Inner membrane (F 3874/220)

Structural material Glass fabric Glass fabricCoating PTFE foil PTFE foilWeight, rawWeight, processed

470 g/m2 ± 10% DIN 53854

1.075 g/m2 ± 10% DIN 52854

315 g/m2 ± 10% DIN 53854

908 g/m2 ± 10% DIN 52854

Yarn count, warpYarn count, weft

EC9 136 × 3 tex DIN 53830

EC 9 34 tex × 2EC9 136 × 3 tex

EC9 136 × 3 tex DIN 53830

EC9 136 × 3 tex

Yarn number, warpYarn number, weft

3.0 + 1.53.5

42

Weave Warp ribs −2 DIN 61101 Lino weaving DIN 61101Width 1.380 mm DIN 53851 1.380 mm DIN 53851

Thickness 1.30 mm DIN 53353 0.98 mm DIN 53353

Maximum tensile force, dry and coated, warp

Maximum tensile force, dry and coated, weft

5.230 N/5 cm ± 10% DIN 53354

4.780 N/5 cm ± 10% DIN 53354

2.218 N/5 cm ± 10% DIN 53354

2.860 N/5 cm ± 10% DIN 53354

Maximum elongation, dry/unidirectional, warp

Maximum elongation, dry/unidirectional, weft

3.0% ± 10% DIN 533543.5% ± 10% DIN 53354

3.0% ± 10% DIN 533544.2% ± 10% DIN 53354

Seam strength (60 mm) 85 kN/mAdhesion of the coating 50–80 N/5 cm Not measuredTranslucency Approx. 65% Approx. 65%Transmission Approx. 50%Shadow effect Approx. 10%Density, glass fabricDensity, PTFE foil

2.60 g/cm = 44%2.18 g/cm = 56%

Arch <3%Fire category A2 DIN 4102 B1 DIN 4102

Flontex). Durability was tested in Laboratorium Blum, Stuttgart, using 10-year-old test strips.

Fire resistance

Tests to establish the fi re resistance of the total construction were done in accordance with DIN 4102 at the Otto Graf Institute of the University of Stuttgart, Germany.

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• Inner membrane with insulation: Class B1, fl ame-resistant• Outer membrane: Class A2, incombustible• Tear-out force: 4000 N/5 cm• No burning parts falling from samples.

Physical calculations to avoid heat bridges

As part of an additional calculation of building physics, heat bridges were investigated with respect to loading by condensation water. Heat bridges are generally permissible in the arched girder because the latter closes off a so-called buffer region, which belongs to the outside and is unheated, against the actual outside area. The inner area is closed off through a sepa-rate inner facade.

The following heat bridges exist:

• Parapet: the arched girders are not thermally decoupled in the parapet region.

• Welded plates: the welded plates serve to rigidly connect the L-section (located on the HEA 240) with the HEA 240, and to rigidly connect the window sashes.

The assumptions used are:

• Inside temperature 18.00°C• Outside temperature −10.00°C• Girder height d = 8 cm• Thermal conductivity of steel = 60.00 W/m2K• Thermal resistance inside, Rsi = 0.17 m2K/W• Thermal resistance outside, Rse = 0.08 m2K/W.

Table 8.5 Physical product assessment (material composition from inside out)

PTFE glass lattice fabric F 3874/220Glass fi bre insulating material, light

glass fabric278 g/m²

PTFE glass lattice fabric F 3874/220Thickness, glass fi bre insulating

material100 mm

Air gap in accordance with DIN 4108 200 mmOverall thickness of the construction Approx. 300 mm Thermal transfer coeffi cient inside αi = 8 W/m2KThermal transfer coeffi cient outside αa = 23 W/m2KSolar radiation In accordance with DIN EN 410Heat exchange coeffi cient U 1.1 W/m2K DIN 4108

Source: Transsolar Climate Engineering Co., Stuttgart, Germany.

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The existing heat exchange coeffi cient is smaller than the relevant coeffi -cient for condensation water. The effect of condensation water is therefore irrelevant since the durability of the facade is not affected.

Functionality of the membrane facade of Terminal EF as a second skin

As the reason for the membrane facade is to build up a second envelope on the west side of the building, it closes up a separate space. This space is used for entrance purposes into the different companies of Terminal EF and offers an additional communication area to all the users.

Physically, the second skin is wrapping the building to create an extraor-dinarily insulated building: in summer, it offers an upwind facade to venti-late the interior to prevent it from overheating; in winter, it is closed and helps to save heating-energy costs (Figs 8.19–8.22).

The facades on each side of the building are made differently and designed according to the external and internal impact factors. All in all, this results in a design which appears as anything but a stereotype: like

Mieteinheit

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8.19 Terminal EF thermal system by Pohl Architekten.

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Zuluftklappen

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Abstützung Druckstab76,1 x 5 und

Auskreuzungen mitZugstabsystem M 10Zuluft

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30 cm Stahlbetondecke

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Stahl - Glas - FassadePfosten-Riegel 50/55

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Scheitellinie Aussenmembranegebogener Untergurt (HEA 240)

Membranekissen, nach Montage der Innen-membrane einzusetzen

Befestigung Innenmembrane,Flachstahlklemme

Keder

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10 - 20 cm Gefällewärmedämmung

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ScheitellinieInnenmembrane

Verbindungsmembrane zwischen Außen- und

Außenmembrane

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HEA 240- Stahlprofil - gekr.

Auflager - Bogenträger aufStahlbetonaufkantung,hergestellt aus Flachstählen

Innenmembranegedämmt

8.20 Terminal EF (detail) by Pohl Architekten.

8.21 Terminal EF (detail) by Pohl Architekten.

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8.22 Terminal EF: details connecting the textile membrane to the steel beams by Pohl Architekten.

plants, which in their natural growing process would react to monotonous climatic conditions by adjusting their stature, or like the way the evolution and protective behaviour of animals led to the fact that the shape of their body and their constitution maintain life functions, the functions, shapes and facades for the building of Terminal EF in Erfurt were developed on the basis of ‘natural’ iterative form-fi nding processes.

Unlike in the scientifi c fi eld of bionics, which tries to understand nature’s processes in a technological way, a kind of ‘bio-technology’ was used for TMZ Erfurt, and the building was developed using all types of methods, cognitive and simulative, whose internal structure looks like an ‘organic being’, and whose outward appearance, along with the choice of the

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functional cover material, has developed components showing interesting parallels between organic and technological development.

Thanks to the combination of membrane and glass facade components on the west side, a high degree of shading along with high light transmission could be achieved. Thanks to the strong light scatter, an even illumination level with a very high percentage of light scatter and diffuse light is given. On one hand, this helps improve working conditions by providing direct insulation without the need for additional shading. On the other hand, a high percentage of daylight can be used even when the sky is cloudy, so that for most of the day artifi cial light is not needed for working in the rooms further back. Costs for electric power are considerably reduced. The fact that employees will fi nd they have almost natural illumination, without having to cope with the problems of over-illumination or extreme insula-tion, is considered a psychologically useful effect for work.

An intelligent fl exible facade with different behaviours in summer and in winter

The impact of heat irradiation in summer is very much reduced by the shading effect of the second-skin facade. For the offi ces located further back, the effect is an upstream buffer zone (Fig. 8.23), which is very well

Natural ventilation

8.23 Terminal EF: system overview of the natural ventilation system by Pohl Architekten.

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controlled as far as ventilation is concerned, thus also considerably reducing heat development in these rooms too, but without the total shading that would otherwise be necessary. Daylight utilization still remains very high (Fig. 8.24).

During the winter, the opposite effect can be observed. The climate buffer of the upwind facade can now work as a heat pit that warms up the work rooms, resulting in a considerable reduction in heating costs. During the winter, the gangway gallery is set to a temperature of 18°C, either by the impact of natural heat, or supported by the heating system (Plate V between pages 168 and 169).

Looking at the west facade, with its alternating glass and membrane fi elds, in terms of the effect of the daylight ratio on the rear of the rooms behind the inner facade, there is little difference from an exterior facade made of glass only. Illumination values are very good throughout the areas at the back of the rooms up to a depth of 6 m. This effect can be explained by the high percentage of diffuse light scatter, which non-directionally illuminates the depths of the rooms. Similar solutions have been tried and carried out, so far, in complex technical systems, i.e. by using glass prisms for the window areas.

Figure 8.25 Terminal EF: System overview of the thermal system to activate thermal building masses in addition to the second-skin facade of the building’s west side.

Natural lighting

8.24 Terminal EF: system overview of the daylight system by Pohl Architekten.

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Erdwärmenutzung

Betonkernaktivierung

8.25 Terminal EF: system overview of the thermal system to activate thermal building masses in addition to the second-skin facade of the building’s west side by Pohl Architekten.

Purpose of the overall concept as regards construction physics and building technique

• High comfort level• Natural ventilation• Thermal comfort• Low energy consumption• Utilization of natural night cooling• Utilization of regenerative energy• Reduction of technical systems in favour of physical construction

processes• Individual control and regulation• Sustainability.

Energy concept

Thanks to close interdisciplinary cooperation, the planning parties involved in the construction succeeded in meeting the parameters for a sustained, innovative building. The infl uencing factors and their effects were revealed

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in iterative processes, compared to each other and translated into the building draft. The computer simulations and the planning of the build-ing both had an infl uence on each other. The sustained ‘intelligence of the building’ was created by intelligent handling of the construction physics and utilization of a modern electrical supply network system and facility management technology, based on results from simulations and examinations.

Thermal simulation of the building: fl ow and illumination simulations

Thermal and fl ow simulations were carried out for the access areas and for offi ce spaces that could generally be compared to each other. Additionally, illumination simulations were carried out for these areas (Plate V between pages 168 and 169), including examination of the variations in different construction materials, as well as diverse sun protection variations. These examinations were carried out in connection with economic calculations of heat and cold production, together with the utilization of regenerative energy sources and economic calculations of daylight utilization. A well-coordinated, sustained system could be developed for the entire building, as far as heating/cooling, ventilation, illumination and the application of thermally activated physical building masses were concerned.

Purpose of the calculated simulations

• Selection of appropriate sun protection measures• Calculation of summer and winter comfort in the gangways and the

offi ces• Dimensioning of thermal concrete activation• Dimensioning of the ventilation outlets for natural ventilation of the

gangways and supply of fresh air to the offi ces• Elaboration of a natural ventilation concept with recommendations for

its regulation.

The construction of the covering for the connection bridges (Figs 8.26 and 8.27)

The covering of the connecting bridge is a mechanically and geometrically pre-stressed membrane roof with an anticlastic curvature. The membrane runs between elliptical tubular steel ties (Fig. 8.28). The lower edge com-prises an embedded arching steel rope. The other edges are captured in Keder profi les (Fig. 8.29) The membrane tension is increased by pulling in the direction of the ties. The membrane material is a PTFE glass fabric laminate (glass-fi bre carrier fabric, Tefl on foil laminate).

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8.26 Terminal EF: connection bridge covered with translucent fabric by Pohl Architekten.

8.27 Terminal EF: connection bridge by Pohl Architekten.

8.28 Terminal EF: connection bridge internal view showing the elliptical steel beams covered with translucent PTFE fabric by Pohl Architekten.

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8.29 Terminal EF: connection bridge detailing by Pohl Architekten.

Static calculation of the membrane of the connecting bridges

The calculation is based on membrane theory, with the following load assumptions:

• Material weight 0.02 kN/m2

• Pre-stress: two-axis pre-stressing to protect the membrane against fl ap-ping and tearing. In addition, pre-stressing prevents wind-induced oscil-lation, so the membrane dampens oscillations in the entire structure. Loading reduces the pre-stressing. Loading by snow and wind is there-fore not superimposed on loading by pre-stressing.

• Applied pre-stressing: v = 1.50 kN/m• Wind load: height above ground 13.0 m, back pressure 0.8 kN/m2

• Pressure coeffi cients for wind-parallel exterior walls 18.50/62.25 = 0.30, weighted 0.70

• Snow load zone 2 → 0.75 kN/m2

The calculated loads for the supporting structures are:

• Load case for edge ropes: Nmax 3.63 kN• Weight, rope diameter 8/1 × 37 DIN 3054, min. breaking strength

54.8 kN, 0.85 × 54.8 kN/3.63 kN = 12.8 > 2.2.

Other membrane details are as follows:

• Membrane of PTFE-coated glass fabric, Type II• Short-time tear strength N = 50 kN/m• Max. membrane loading occurs in load case snow + wind pressure:

8.00 kN/m

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• Reduce by 15% for manufacturing tolerances: reduction factor 0.85• After ageing, material and manufacturing data, and installation toler-

ances, an overall reduction of ages = 3.00 is assumed.• The safety factor is as follows: ν = 50/(3.00 × 8.00) × 0.85 = 1.77 > 1.3erf.

The same material as for the outer membrane was used for the membrane bridges; the inner membrane differs from the outer membrane. The Keder profi le was Co. Piper aluminium Keder profi le 1534.

8.4 Future trends

In future, the necessity of reducing energy as well as minimizing the con-sumption of resources such as massive and heavy building materials will lead us to intelligent building systems. Textile materials will play an inter-esting role in the available components market. All national greenhouse standards will focus on how architects can manage to achieve high living standards together with a minimum use of energy.

Of course, there are many more possibilities than the examples shown. They just focus on the theme in general and may be helpful for the discus-sion of future building systems. Other examples of materials include pneu-matic systems or even fi bre-reinforced materials, hybrid materials that combine different elements for additional functions. In the future, for example, windows may be used not only to obtain daylight, but also as solar collectors, as media facades, and as fl exible facades with different proper-ties for summer and winter.


Examples can be found in the following list. A good overview with more information can be found at www.tensinet.com.

Raw material

Kastilo Technische Gewerbe Vertriebs GmbHAugust-Nagel-Straße 16, D-89079 Ulm-Einsingen, GermanyTelephone: +49 (7305) 96900, fax: +49 (7305) [email protected], www.kastilo.de

PTFE-coated fi breglass

Membrantechnik Flontex GmbH, Hofäckerenstrasse 14, CH-9425 Thal, Switzerland

Telephone: 0041 71 440 13 30, fax: 0041 71 440 13 31

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Taconic USA, 136 Coonbrook Road, P.O. Box 69, Petersburgh, NY 12138, USA

Telephone: +518.658.3202, fax: +518.658.3988Taconic International Ltd, Mullingar Business Park, Mullingar, Co.Westmeath, Republic of IrelandTelephone: +353.44.40477, fax: +353.44.42514Korea Taconic Company Ltd, NA-906-2, APT Factory 148, Yatap-dong,

Bundang-ku Sungnam SI, Kyung’GI-DO, Republic of KoreaTelephone: +82.342.704.1858, fax: [email protected]

Silicon-coated fi breglass

P-D Interglas Ltd, Sherborne, Dorset DT9 3RB, UKTelephone: +44 1935813722, fax: +44 [email protected], www.atex-membranes.com

Insulation systems, spun glass matting

Wacotech GmbH & Co. KG, Gewerbepark Brake, Querstraße 7, D-33729 Bielefeld, Germany

Telephone: +49 (0)521 96200-80, fax +49 (0)521 [email protected], www.wacotech.de

8.6 References and bibliography

Baier, Bernd et al., Transparenz und Leichtigkeit. Interdiszipläres Symposium. Verlag der Universität Duisburg-Essen, 2003

Baier, Bernd et al., Grenzbereiche Leichte Konstruktionen. Interdiszipläres Symposium Essen für konstruktive Gestaltung und Leichtbau. Verlag der Universität Duisburg-Essen, 2005

Buckminster Fuller, Richard, Your Private Sky. Design als Kunst einer Wissenschaft. Verlag Lars Müller, 2000

Büttner, Oskar and Hampe, Erhard, Bauwerk, Tragwerk, Tragstruktur, Vols 1 and 2. Niggli Verlag, 1967

Dubois, Marc, Philippe Samyn: Architecture and Engineering 1990–2000. Birkhäuser, 1999

Hubert, Alain, president of the International Polar Foundation, in the conference Du bois dans les glaces éternelles, Luxembourg, 2008

Kost, Michael, Langfristige Energieverbrauchs- und CO2- Reduktionspotentiale im Wohngebäudeordner Schweiz. Dissertation, ETH Zürich, 2006

LeCuyer, Annette, ETFE Technologie und Entwurf. Birkhäuser, 2008Otto, Frei, Spannweiten. Ideen und Versuche zum Leichtbau. Ullstein Verlag, 1965Otto, Frei, Bodo Rasch: Gestalt fi nden. Axel Menges, 1995Otto, Frei, Das Gesamtwerk: Leicht bauen – natürlich gestalten. Birkhäuser, 2005

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Pohl, Göran, Technologie- und Medienzentrum in Erfurt – Gebäude mit Zukunft. Intelligente Architektur, 11–12, 2002, Kohlhammer-Verlag

Pohl, Göran, Technology and Media Centre in Erfurt, in: Tensinet Symposium Designing Tensile Architecture. Vrije Universiteit Brussel, 2003, pp. 52–64

Pohl, Göran, Konstruktive Architektur – Leicht und Weit, in: Bernd Baier et al., Reichweiten – Leichte Konstruktionen. 5. Interdiszipläres Symposium Essen für konstruktive Gestaltung und Leichtbau. Verlag der Universität Duisburg-Essen, 2006, pp. 69–93

Seidel, Michael, Textile Hüllen: Bauen mit Biegeweichen Tragelementen. Ernst & Sohn, 2008

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290

9Learning from nature: lightweight constructions

using the ‘technical plant stem’

M. MILWICH, Institute for Textile Technology and Process Engineering Denkendorf (ITV), Germany and

T. SPECK, Universität Freiburg, Germany

Abstract: Because of their many advantages, fi ber composites are increasingly used in airplanes, space shuttles and racing cars, but also in modern construction and building. Lightweight fi ber reinforced plastics (composites) are being substituted for traditional load-carrying iron–concrete primary materials or outer and inner paneling materials like wood or non-reinforced plastics. This chapter describes the biomimetic development of a technical plant stem from the role model of plant stems, which will be useful in building and other technical applications.

Key words: technical plant stem, technical textiles, biomimetic, natural role model.

9.1 Introduction

Because of their manifold advantages, fi ber composites are increasingly used in airplanes, space shuttles, racing cars and sporting goods, but also in modern construction and buildings. Lightweight fi ber reinforced plastics (composites) are being substituted for the traditional load-carrying iron–concrete primary materials or outer and inner paneling materials like wood or non-reinforced plastics. With the use of strong fi bers such as glass, carbon, or aramid and their embedment in polymer, metallic or ceramic matrices, very strong and lightweight composite materials and structures can be pro-cessed. Advantages of composites are:

• High strength and stiffness and low fatigue combined with a low weight

• Good thermal insulation• Great variety of possible forms and colors• Very good corrosion resistance and resistance to environmental

conditions• Less energy consumption for production.

Several bridges have been built and are in service using fi ber composite materials for load cables and bridge decks, having the advantages of being

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Lightweight constructions using the ‘technical plant stem’ 291


lighter, the material being non-corrosive and providing much higher fatigue limits. Usually the load cables and decks are produced with the cost-effective pultrusion technology, where thermoset matrix impregnated fi ber strands are pulled through a heated die, the matrix being cured during the passage through the die. In continuation of this technique to produce rein-forcing profi les, American architect Peter Testa has proposed building a high-rise building (the ‘carbon tower’) of thick strands of helically and circumferentially wound, pultruded carbon fi ber composites arranged in a mesh, with the spaces between the strands fi lled with glass plates.

For paneling, the relatively big but thin composite parts are produced using pre-impregnated materials (prepregs) or dry textiles. Prepregs are stacked on each other onto a form, covered with a vacuum bag, and con-solidated in an autoclave. Dry textiles are usually draped into a form and then impregnated and consolidated with a resin transfer molding technique or vacuum bagging.

Today, composites are used widely and are undergoing development. Research is being conducted into reducing production costs, developing more sophisticated methods for constructing ultimate lightweight structures, and creating higher functionality – so called ‘smart functions’, the functional-ity preferably deeply integrated into the textile or the fi ber. Examples of such functionalities are (1) passive, form-optimizing adaptive wings for maximum energy yield of airplane wings or wind turbine blades (Breitbach and Sinapius, 2004), (2) integrated (fi brous) glass sensors for damage control in buildings, bridges and airplanes, and (3) active damping for disturbing or harmful vibration with piezo-ceramic fi bers (Monner, 2005).

An advantage of using fl exible fi ber material is that, as in nature, the fi bers can be laid exactly in the direction of the strain lines of a designed structure. Ultimate lightweight composite structures are thus manufactured with so-called ‘gradient textile techniques’. When using gradient textile techniques, every single fi ber strand is exactly laid within the structure, in the direction of the applying forces in order to save weight, resources and energy. As an example made by a gradient textile process, Figure 9.1 shows an extreme lightweight carbon fi ber reinforced plastic, ‘Robot-arm’, from the German company Kuka Roboter GmbH, produced by a process called tailored fi ber placement. This is in principle a stitching process, where, on a slightly altered textile stitching machine, up to 10 stitching heads place every single carbon fi ber strand next to the preceding fi ber strand (Fig. 9.2).

9.2 Using biomimetics to enhance the lightweight

potential of composites

Fiber reinforced composites are a classic example of biomimetic translation of nature’s wisdom into technology. Many principles of composites have

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9.1 Extremely lightweight carbon fi ber-reinforced plastic robot arm, produced by tailored fi ber placement (courtesy of Kuka GmbH, Germany).

9.2 Example of a tailored fi ber placement preform.

their counterpart in nature. Bones, plant stems, and wood have highly opti-mized the use of fi bers in the exact directions of effective loads (Mattheck, 1990, 1996, 1998; Vogel, 1998) and are emulated by various textile methods. The optimized microscopic fi ber arrangement in biological materials fi nds its extension in an optimal macroscopic arrangement of struts for load-carrying structures.

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Figure 9.3 shows the thorax of a dragonfl y, in which the ribs themselves are weight-optimized structures and are macroscopically arranged as weight-saving spacer structures connected by a thin layer of outer skin. The lightweight potential of this arrangement is self evident.

Figure 9.4 shows, for example, the macroscopic wood arrangement of the stem of a cactus, which found its biomimetic counterpart in the Rotex robotic arm, made manually by DLR Germany, with 0° and 90°-fi ber

9.3 Illustration of an exoskeleton (thorax) of a dragonfl y (courtesy of Prof. Nachtigall, Saarbrücken University, Germany).

9.4 Robotic arm modeled after cactus wood (courtesy of DLR Stuttgart, Germany).

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bundles (tensile/compression/bending forces) and 45°-fi ber bundles (torsional loads).

To support the manufacturing of ultra-light composites, Claus Mattheck from the Forschungszentrum Karlsruhe developed several ‘fi nite element’ computing methods after the role models of wood and bones. Claus Mattheck investigates and defi nes biological design rules which are then applied to optimize the shape of composites in accordance with naturally growing biological constructions. The computing methods of Claus Mattheck simulate force-controlled biological growth, which helps to optimize techni-cal constructions by a similar ‘organic’ growth (as in trees) or even helps to remove unnecessary volume and weight (as in bones) (Mattheck, 1990, 1996, 1998). His propagation of using tension force-loaded machine ele-ments instead of using pressure-loaded elements under the motto ‘Thinking in Ropes’ for lightweight construction will further advance the use of custom-made composites (Mattheck et al., 2004).

A further successful transfer from biological composites into technical applications dates back to the early 1980s and was accomplished by the group of R. Gordon, C. R. Chaplin, and G. Jeronimidis at Reading University. They patented a bio-inspired composite structural panel with high strength and toughness (Chaplin et al., 1983) based on (ultra-)structural features in wood (Gordon and Jeronimidis, 1980; Jeronimidis, 1980, 1991). The orienta-tion of the fi bers in this biomimetic composite is based on angles found in micro-fi brils of wood tracheids.

Although fi ber composites are widely used, scientists think that there is a lot more to learn from nature in the fi eld of composites. The fi ber arrangement of biological systems is yet to be fully understood, as well as the high vibration damping ability of plants, the wide use of pre-stressing fi bers to increase compressive strength, or the ability of pine cones to withstand high burning temperatures. Because of the complexity of biological systems, modern biomimetics is a systematic approach of collaborating researchers from different scientifi c backgrounds developing new ideas from looking into an abundance of biological role models. In this context, biologists, chemists, physicists and engineers within the German Network ‘BIOKON’ and the Baden-Württemberg Competence Network Biomimetics (Universities of Freiburg, Stuttgart and Tuebingen, and Forschungszentrum Karlsruhe) work together with the Institute of Textile Technology and Process Engineering in Denkendorf (ITV) to explore nature’s ‘smart functions’ as a source for textile solutions (Stegmaier et al., 2004; Harder, 2006) and composite applications. The interdisciplinary approach of the network members ensures that results from basic biological research are transferred into industrial products throughout the whole value chain. Often the conversion of natural prin-ciples into technical applications is made by means of textile technologies,

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because textiles techniques, like nature, also assemble from small to big, from (nano-scale) fi bres to big superstructures.

The bionic development known as the ‘technical plant stem’ presented in the following pages will show again strikingly how biomimetics can further enhance the performance of composites. This smart functional com-posite and lightweight structure developed from plant stem role models enables, through its special design, still higher buildings or bridges of even wider spans, together with the possibility of guiding electrical or other energy lines through incorporated channels. It uses extensively the principle of ‘anisotropy’ of biological systems to arrange vectored fi bers only in the areas of the structure where they are needed to carry the loads, but simul-taneously in such a manner that other important functions can be fulfi lled additionally, for example water transport.

Yet, in future, traditional engineering will still be the basis of most new technical developments, because biomimetics cannot and will not replace this established and well-tested approach. But new developments, whenever possible and however ingenious, will be stimulated by solutions from nature and compared with nature’s wisdom, thus generating a pool of ideas and knowledge for further use. The mostly superfi cial, functional knowledge gained from past research can now be supplemented with new fi ndings about the fi ne structure of materials or the functions of boundary layers using new measuring methods, which are able to unearth the natural prin-ciples or regularities hitherto unknown.

9.3 Exploiting plant role models for technical use

For the construction of ultra-lightweight technical structures, Dutch rush or horsetail (Equisetum hyemale) (Fig. 9.5), giant reed (Arundo donax) (Fig. 9.6) and conifer wood were identifi ed as particularly promising biomimetic role models because of the superior mechanical and lightweight properties of their stems (Speck and Spatz, 2001; Speck et al., 2005, 2006). With those natural examples in mind, a joint brainstorming by biologists from Freiburg and engineers from ITV Denkendorf recombined and abstracted those natural functionalities and searched for possibilities for transferring them into technical structures.

9.3.1 Wood

An interesting structure can be found in wood, for example in the different layers of conifer tracheids, where helically arranged cellulose micro-fi bril bundles are found (Fig. 9.7). The spiral-like lay-up and the angle of the strengthening fi bers in the stem walls and of cellulose micro-fi bril bundles in the cell walls is optimized according to the types and combinations of

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9.5 Cross-section of the stem of horsetail (Equisetum hyemale).

9.6 Cross-section of the stem wall of giant reed (Arundo donax).

mechanical loading occurring in the plant stem, e.g. static or dynamic bending and torsion or oscillating movements (Mark and Gillis, 1973; Cave and Walker, 1994; Reiterer et al., 1999; Burgert et al., 2004, 2005). A fi ber angle of 15° is most common, though the reason for this special angle is yet to be proven from the engineering side.

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Bionic abstraction of wood properties and transfer into techniques

As in wood and other plants, spirally arranged fi bers improve torsional stabil-ity and oscillation damping of technical goods. With computer-controlled braiding techniques available at ITV Denkendorf, helically wound fi bers can be easily incorporated into the composite structure, whereas the angle of fi bers and fi ber bundles can be adjusted to the predominant loading situation(s) of the application mode of the fi nished component. Thus, opti-mally designed technical structures can be produced.

9.3.2 Horsetail

The hollow aerial stem of horsetail (Equisetum hyemale) represents an extremely lightweight construction. Functional analysis identifi ed a double ring structure in strengthening tissues, consisting of an outer ring of fi brous collenchymatous tissues that are connected to the inner, double-layered endodermis by ‘pillar-like structures’ having the appearance of T-struts in cross-section in the stem periphery (Fig. 9.8). Between the collenchyma and the endodermis, which resembles a technical sandwich structure, is a thicker layer of parenchymatous tissue with remarkably large so-called vallecular canals, signifi cantly reducing the weight of the hollow stem (Speck et al., 1998; Spatz and Emanns, 2004). The hollow stems of the giant reed Arundo donax (see Section 9.3.3) grow up to a height of 6 m with a basal outer diameter of approximately 2 cm. They also have excellent mechanical

9.7 Polarized light microscopy of compression wood of spruce (Picea abies), image of helical cellulose fi bers in adjacent cell walls (courtesy of Dr I. Burgert, Max Planck Institute of Colloids and Interfaces, Potsdam/Golm, Germany).

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9.8 Detail of cross-section of the stem of horsetail (Equisetum hyemale).

properties under both static and dynamic loading conditions (Spatz et al., 1997; Speck, 2003; Speck and Spatz, 2003). If the dense stands are subjected to dynamic wind loads, the slender columns respond with bending vibra-tions and pronounced damping (Speck, 2003; Speck and Spatz, 2004).

Several structural design principles, which are also fundamental to theo-retical mechanical engineering, contribute to these outstanding mechanical properties. The most obvious optimized structural design is the double ring structure of Equisetum hyemale. This principle is well known in mechanical engineering. In load-carrying beams, most of the material of the beams should be placed (or spaced) at the utmost possible distance from the center of the beam (neutral line), this being the reason for developing the double T-beams. The structure of Equisetum hyemale anticipated one of the most widely applied structural principles in building bridges and houses and just looks like double T-beams welded together (Fig. 9.9).

The same principle is also applied in building cars (space frame structure) or airplanes. In airplanes, the honeycomb or foam cores in ‘spacer’ sandwich composites multiply the bending resistance of structures. Figure 9.10 illus-trates this principle. The left, thin side of the specimen is comprised of two layers of glass woven fabric embedded in a matrix material and has a bending resistance defi ned as 1. In the thicker, right side of the specimen, a foam core is included between the skin layers. This part has a bending moment 40 times higher than the left side without the core.

For the same reason, hollow tubes also have very good specifi c bending resistance, but if the skin of the tube is very thin, buckling will arise, and the structure will need a supportive inner framework, either a foam core or a fi brous core (Niklas, 1989, 1992, 1997; Mattheck, 1996, 1998; Spatz and Speck, 1994; Spatz et al., 1997; Speck et al., 1998; Mattheck et al., 2006).

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Bionic abstraction of horsetail properties and transfer into techniques

With its double ring structure with connecting cross-beams, Equisetum hyemale could be a role model for a superior lightweight construction with high compression capacity and high bending stiffness. This structure of Equisetum hyemale can actually be produced with the so-called braid-pultrusion technology, the basic equipment already installed at ITV Denkendorf. For producing a similar effective structure the braid pultru-sion line was specially adapted. The vallecular canals between inner and outer ring and the connecting cross-beams of E. hyemale work as an addi-tional means of gas exchange and store water from the cells to prevent frost damage. As technical analogs of the vallecular canals, the so-called func-tional canals could be used to transport electrical power via power supply lines or liquids and gases via pipes (see Fig. 9.8).

9.9 Double ring structure with connecting beams, similar to Equisetum hyemale, ‘constructed’ out of welded double T-beams.

9.10 Increasing bending stiffness of composites using a foam core.

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9.3.3 Giant reed

The hollow stems of the giant reed (Arundo donax) offer another astonish-ing sort of ‘core’: a sophisticated, weight-optimized structure with a material optimized to dynamic loads. The stems are composed of strengthening ele-ments such as vascular bundles and accompanying fi ber caps, which are embedded in a matrix of basic parenchyma (see Fig. 9.6). In cross-section, at least four structural gradients on different hierarchical levels can be found, which meet also all theoretical considerations and needs of technical composite structures.

1. In the periphery of the hollow stems, the area of highest stress, most of the load-carrying fi ber material is placed. Then, the amount of load-carrying material is gradually reduced in the direction of the stem’s hollow core, in keeping with the gradual decrease in bending stress as the distance from the periphery increases.

2. This mechanical grading is also exemplifi ed by the lignifi cation of the parenchymatous basic tissue as it decreases in a radial direction from the outside toward the center.

3. An additional gradient in the basic parenchyma can be found: the increasing size of the parenchyma cells is accompanied by gradually thinner cell walls from the outside to the inside of the stem wall, causing a reduction of the relative cell wall amount.

4. The gradient in the macro-superstructure in (1) fi nds its counterpart in a micro-structural phenomenon. The pronounced difference in stiffness between natural fi bers and the surrounding parenchyma matrix is equalized by a gradual transition in stiffness. This results in a very high damping of oscillating wind forces and a high bending ability with optimal distribution of stress before the connection between fi bers and matrix fi nally fails and the structure disintegrates. This is illustrated by Fig. 9.11, which shows a bending test of an internode of the hollow stem of Arundo donax. After each of the 10 smaller ruptures, the structure stabilizes itself through the distribution of stress and can then tolerate even more stress until the fi nal failure. This graph is a very good example of a mechanically benign, ductile rupture failure and could be a model for any load-carrying technical structure (Spatz et al., 1997; Speck et al., 2006).

Bionic abstraction of giant reed properties and transfer into techniques

According to the gradually decreasing bending stress with increasing distance from the outer periphery of the plant stem, the amount of load-carrying material is also gradually reduced concurrently with a gradual

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reduction of cell wall thickness and an increase of cell size of the parenchy-matous basic tissue.

As ‘gradient textile technologies’ already demonstrate, fi bers should only be incorporated where they are useful in carrying loads. In less stressed parts of a construction, polymer foam will be used for spacing out fi bers. With the braid-pultrusion technique, this principle can be applied very easily into the structure.

In summarizing, the structural basis of the graded transition of Young’s modulus between stiff fi ber and less stiff parenchyma matrix is a gradient in lignifi cation between fi bers and parenchymatous cells and of variations in cell size and cell wall thickness. Transferring this knowledge into tech-niques, the stiffness between fi bers and matrix will also be graded using a matrix material that can be provided by varying Young’s modulus.

9.3.4 Combining different principles of the role models into the ‘technical plant stem’

Whereas other bionic solutions in the fi eld of composites are mostly founded on a single natural function, the seven different natural functionalities mentioned above were combined and translated into a concept of a techni-cal fi ber composite material with superior mechanical properties. A fi rst computer modeling of the structure is shown in Fig. 9.12. The advantages of the new composite material were self-evident in such a way that special-ists from prominent composite companies – seeing the FEM calculations and later the fi rst prototypes of the technical plant stem – encouraged the inventors to patent this so-called ‘technical plant stem’.

Pre-failureincidents

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9.11 Bending test of an internode of Arundo donax to show the relationship between bending moment and curvature. Arrows mark initial failure and fi nal failure. In between, a series of several partial collapses can be found.

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9.4 Production of the ‘technical plant stem’

Nevertheless, the production costs for combining these functionalities into a new, unique product must always be considered. In the case of composite beams, the pultrusion process is a cost-effi cient production method for endless-fi ber-reinforced plastics. Compared to metals, the pro-fi les are corrosion resistant and to a large degree maintenance free. They are very safe in having good electrical and thermal isolation, installation costs are lower, and lighter foundations can be realized. In thermoset pultrusion, impregnated high-performance fi bers are pulled through a form-shaping die and are consolidated by heat and pressure during transit through the die.

One of the desired features of the technical plant stem is improved tor-sional stability and oscillation damping. As mentioned, the diagonal fi ber bundles can be incorporated into the technical plant stem via a braiding machine, which was installed in-line with the pultrusion process (Figs 9.13 and 9.14).

The braiding technique (Fig. 9.15) helically winds two different counter-rotating sets of intertwining fi ber strands around a core system and an inner layer of unidirectional fi bers. By varying the density, arrangement and angles of the fi bers in the different layers of the technical plant stem, the resulting fi ber structure of the technical plant stem can be optimally designed for a given load situation. In a fi rst approach, different hollow profi les with glass fi ber reinforcement were pultruded and braid-pultruded, optimizing both process and machinery (Fig. 9.16). The fi rst samples of technical plant stems were braided and impregnated (Fig. 9.17) with poly-urethane resin by the vacuum bagging method. In the next step of optimiza-tion, the rigid polyurethane matrix was again used to encase micro-fi brils

Y

XZ

9.12 FEM modelling of the technical plant stem.

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9.13 ITV braid-pultrusion technology.

9.14 Detail of ITV braid-pultrusion technology.

and fi ber bundles. But to mimic the porous, optimized weight potential of the plant–matrix system, a polyurethane foam matrix was applied between the fi ber bundles, resulting in a very lightweight specimen (Fig. 9.18). The braid-pultruded technical plant stem can be seen in Fig. 9.19, showing the principle of applicability of the braid-pultrusion process.

By combining this cost-effi cient production method with the several advantages of the technical plant stem, this unique material will rapidly spread into manifold applications in the composite world.

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9.15 Braiding technique.

9.16 Braid-pultruded tubular profi le with thermoset matrix.

9.5 Applications of the ‘technical plant stem’

There are numerous applications for the ‘technical plant stem’. In most cases, where tubular rods are used – and there is an abundance of applica-tions for tubular rods – the structure of the technical plant stem will enhance the performance of the original rod in terms of mechanical properties like pressure resistance or bending stiffness. Either the rods will be stiffer and stronger or the rods will be lighter than other composite materials. Therefore aerospace, automotive, building, and sporting goods can profi t from this new development.

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In the building industry, if the rods are used to build a load-carrying structure under the roof, the structure is assembled very quickly with less manpower and the foundations could be made lighter (Fig. 9.20). This is the same as in telescope structures, which need a stiff yet lightweight construc-tion, because the whole structure will be moved into a desired direction (Fig. 9.21).

9.17 ‘Technical plant stem’, hand impregnated.

9.18 ‘Technical plant stem’ with polyurethane foam matrix.

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9.19 ‘Technical plant stem’, braid-pultruded.

9.20 Application of ‘technical plant stem’: lightweight load-carrying roof substructure (courtesy Exel-Oy).

In other cases, the multi-channel system will offer new functionalities like integrated gas, fl uid or power transport. A very interesting application in the building industry would be the use of the side channels for incorporat-ing pultruded carbon composite rods. The carbon rods could be incorpo-rated and fi xed during the pultrusion process of the technical plant stem under a certain pre-tension load. The use of the technical plant stems as

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tension members in concrete would make elaborate on-site pre-tensioning of steel superfl uous.

9.6 Future trends

Many other astonishing plant functionalities are waiting to be discovered. The interdisciplinary collaboration of researchers with biological, chemical, physical, and engineering backgrounds and a systematic biomimetic approach to comprehend biological structures, processes, and functionality will bring new insights for the development of new technical solutions. In our opinion, technical textiles and fi brous composite materials offer a bril-liant opportunity for transferring ideas inspired by biological models via biomimetic approaches into innovative technical structures, because com-posite materials based on technical textiles allow production processes comparable to those used by nature (Milwich et al., 2006, 2007).

Despite the many advantages of composites, one of their biggest prob-lems, especially in the building sector, is that the polymeric matrix is com-bustible in general and that over 200°C the polymeric matrix systems become weak. Phenolic resins or cyanate ester resins are somewhat better suited because they are fl ame resistant, but also fi re will damage the struc-ture much more quickly than steel-reinforced concrete. To constitute com-posites on a larger scale in the building industry, this problem has to be solved. As mentioned, maybe nature also could provide some interesting solutions to this problem.

For composites, the way into the future is already predetermined by nature: combining the lightweight nature and energy-saving potential in production and use of composites with a better recycling ability. Improving the recycling ability, e.g. with the use of biodegradable natural fi bers and

9.21 Application of ‘technical plant stem’: stiff and lightweight substructure for a telescope.

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bio-matrix systems, the future use of composites will quickly increase. The development of the ‘technical plant stem’ will strongly contribute to future developments.

9.7 References

Breitbach, E., and M. Sinapius. 2004. Stand und Perspektiven des Leichtbaus und der Adaptronik. Jahresbericht des DLR Instituts fuer Strukturmechanik, Braunschweig, Germany.

Burgert, I., K. Fruehmann, J. Keckes, P. Fratzl, and S. E. Stanzl-Tschegg. 2004. Structure–function relationships of four compression wood types – Micromechanical properties at the tissue and fi ber level. Tree Structure and Function 18: 480–485.

Burgert, I., N. Gierlinger, and T. Zimmermann. 2005. Properties of chemically and mechanically isolated fi bres of spruce (Picea abies [L.] Karst.). Part 1. Structural and chemical characterization. Holzforschung 59: 240–246.

Cave, I. D., and J. C. F. Walker. 1994. Stiffness of wood in fast-grown plantation softwoods: the infl uence of micro fi bril angle. Forest Products Journal 44: 43–48.

Chaplin, C. R., J. E. Gordon, and G. Jeronimidis. 1983. United States Patent. Composite Material. Assignee: Westvaco Corporation, New York, application 351,777.

Gordon, J. E., and G. Jeronimidis. 1980. Composites with high work of fracture. Philosophical Transactions of the Royal Society of London A 294: 545–550.

Harder, D. (ed.) 2006. BIOKON Bionik-Kompetenz-Netz – Creative transfer of biological principles into engineering. BIOKON e.V. Bionics Competence Network, Berlin.

Jeronimidis, G. 1980. Wood, one of nature’s challenging composites. In J.F.V. Vincent and J.D. Currey (eds), The Mechanical Properties of Biological Materials, Symposia of the Society for Experimental Biology 34: 169–182. Cambridge University Press, Cambridge, UK.

Jeronimidis, G. 1991. Learning from nature: biological composites. Proceedings of Inaugural European Seminar, Arche de la Défense, Paris.

Mark, R. E., and P. P. Gillis. 1973. The relationship between fi ber modulus and S2 angle. Tappi 56: 164–167.

Mattheck, C. 1990. Engineering components grow like trees. Materialwissenschaft und Werkstoffkunde 21: 143–168.

Mattheck, C. 1996. Trees – the Mechanical Design. Springer Verlag, Heidelberg, Germany.

Mattheck, C. 1998. Design in Nature – Learning from Trees. Springer Verlag, Heidelberg, Germany.

Mattheck, C., R. Kappel, I. Tesari, and O. Kraft. 2004. In Seilen denken – Einfache Anleitung fuer Naturnahes Konstruieren. Konstruktionspraxis 9: 26–29.

Mattheck, C., K. Bethge, and I. Tesari. 2006. Shear effects on failure of hollow trees. Trees – Structure and Function 20: 329–333.

Milwich, M., T. Speck, O. Speck, T. Stegmaier, and H. Planck. 2006. Biomimetics and technical textiles: solving engineering problems with the help of nature’s wisdom. American Journal of Botany 93: 1295–1305.

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Milwich, M., H. Planck, T. Speck, and O. Speck. 2007. The technical plant stem: a biomimetically inspired narrow fabric. Melliand – Narrow Fabric and Braiding Industry 44: 34–38.

Monner, H. P. 2005. Smart materials for active noise and vibration reduction. Proceedings of the Novem – Noise and Vibration: Emerging Methods, Saint-Raphael, France.

Niklas, K. J. 1989. Nodal septa and the rigidity of aerial shoots of Equisetum hyemale. American Journal of Botany 76: 521–531.

Niklas, K. J. 1992. Plant Biomechanics. An Engineering Approach to Plant Form and Function. University of Chicago Press, Chicago.

Niklas, K. J. 1997. Responses of hollow, septate stems to mechanical vibrations: evidence that nodes can act as spring-like joints. Annals of Botany 80: 437–448.

Reiterer, A., H. Lichtenegger, S. Tschegg, and P. Fratzl. 1999. Experimental evidence for a mechanical function of the cellulose microfi bril angle in wood cell walls. Philosophical Magazine A 79: 2173–2184.

Spatz, H.-CH., and A. Emanns. 2004. The mechanical role of the endodermis in Equisetum plant stems. American Journal of Botany 91: 1936–1938.

Spatz, H.-CH., and T. Speck. 1994. Local buckling and other modes of failure in hollow plant stems. Biomimetics 2: 149–173.

Spatz, H.-Ch., H. Beismann, F. Bruechert, A. Emanns, and T. Speck. 1997. Biomechanics of the giant reed Arundo donax. Philosophical Transactions of the Royal Society of London, B, Biological Sciences 352: 1–10.

Speck, O. 2003. Field measurements of wind speed and reconfi guration in Arundo donax (Poaceae) with estimates of drag forces. American Journal of Botany 90: 1253–1256.

Speck, T., and H.-CH. Spatz. 2001. Transkription oder Translation: Pfl anzen als Ideengeber fuer neue Materialien und technische Leichtbaustrukturen. In A. von Gleich (ed.), Bionik, 2nd edn: 229–245. Teubner Verlag, Stuttgart, Germany.

Speck, O., and H.-CH. Spatz. 2003. Mechanical properties of the rhizome of Arundo donax L. Plant Biology 5: 661–669.

Speck, O., and H.-CH. Spatz. 2004. Damped oscillations of the giant reed Arundo donax (Poaceae). American Journal of Botany 91: 789–796.

Speck, T., O. Speck, A. Emanns, and H.-CH. Spatz. 1998. Biomechanics and func-tional anatomy of hollow stemmed sphenopsids: II. Equisetum hyemale. Botanica Acta 111: 366–376.

Speck, O., M. Milwich, D. L. Harder, and T. Speck. 2005. Vom biologischen Vorbild zum marktreifen bionischen Produkt: der ‘technische Pfl anzenhalm’. Museo 22: 96–103.

Speck, T., D. Harder, M. Milwich, O. Speck, and T. Stegmaier. 2006. Die Natur als Innovationsquelle. In P. Knecht (ed.), Technische Textilien: 83–101. Deutscher Fachverlag, Frankfurt, Germany.

Stegmaier, T., M. Milwich, A. Scherrieble, M. Geuer, and H. Planck. 2004. Bionic developments based on textile materials for technical applications. In I. Boblan and R. Bannasch (eds), Fortschritt-Berichte VDI, Reihe 15 Umwelttechnik 249: 323–330. VDI Verlag GmbH, Düsseldorf, Germany.

Vogel, S. 1998. Cats’ Paws and Catapults – Mechanical Worlds of Nature and People. Norton, New York.

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310

10The role of textiles in providing biomimetic

solutions for construction

G. POHL, Saarland University of Applied Sciences, Germany, T. SPECK and O. SPECK, Universität

Freiburg, Germany and J. POHL, Lightweight Constructions Institute, Germany

Abstract: Biomimetics plays an impending role in today’s needs for products that cope with the demands of effectiveness in terms of energy consumption and material use. Especially in the fi eld of architectural textiles, substantial progress is being made. The concerted systematic research in biology, engineering, architecture and other professional disciplines is leading to surprising detections of functional principles in biology, whose implementation in innovative technical solutions could not have been made without the help of nature. A multitude of new materials and constructions is under development, featuring outstanding properties concerning, for example, weight, stability and durability.

Key words: bionics, biomimetics, composites, diatoms, textiles, architecture.

10.1 Introduction

Bionics and biomimetics (both expressions are commonly used), character-ized as a close iterative cooperation in research and development by biolo-gists, engineers and other scientists, play an impending role in today’s needs for products that cope with the demands of effectiveness for technical products in terms of energy consumption and material use. The entire developmental process from the biological concept generator to the mar-ketable biomimetic product is characterized by close cooperation between different disciplines, to share their broad specifi c knowledge. The different partners involved in a biomimetic research and development project, who may come from branches of biology, engineering, architecture, mathematics, informatics, physics, chemistry, geology, hydrology or meteorology, make biomimetic research a specifi c branch in so-called green technologies. Biomimetics is an extremely interdisciplinary research discipline. Depending on the scientifi c expertise of the individual participants, research concen-trates either more on the biological or more on the technical aspects of biomimetics.

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The role of textiles in providing biomimetic solutions 311


In the 1950s and 1960s, J.G. Helmcke as a biologist and Frei Otto as an architect discussed whether it is a coincidence to recognize similarity between living and built structures or whether living structures built accord-ing to ‘natural laws’ are comparable to certain technical structures which Frei Otto named ‘natural structures’. With the help of the research pro-gramme ‘SFB 64 – Weitgespannte Flächentragwerke’ [1], in the years 1970–1985 examinations of living structures were carried out by Frei Otto and his group, which were internationally recognized. These research topics focused on nets in nature and technology, on pneus in living nature and on biology and building. Starting in 1984 and lasting until 1995, the research programme ‘SFB 230 Natürliche Konstruktionen’ [2] followed. It aimed at architecture, urban planning, building construction and design. Herein, pro-cesses of self-construction and self-organization in all parts of living and not-living nature and in technology were studied, as well as mechanisms of animal and human behaviour in the context of housing and cities and in the context of aesthetics of natural and technical constructions.

10.2 Defi nitions of biomimetics, bionics and

technical biology

Biomimetics is a portmanteau word fabricated from the words biology and mimesis (imitation). Its contents are essentially identical with the term bionics (today combined from biology and technics). As alternatives to ‘bionic’ or ‘biomimetic’, the terms ‘biologically inspired’ or ‘bio-inspired’ are sometimes used.

The term ‘bionics’ was established by Jack E. Steele in 1958 and used as an offi cial term in a USAF Conference in 1960 [3]. Bionics was originally an expression for the combination of biology and electronics.

‘Technical biology’ was established by Werner Nachtigall as a comple-mentary item to biomimetics (bionics) [4–7]. Technical biology stands for the analysis of form–structure–function relationships in living organisms using methodological approaches from physics and engineering sciences. Technical biology is the basis of many biomimetic research projects allow-ing the functioning of the biological templates in a quantitatively and tech-nologically based manner to be understood. These quantitative analyses are the basis for abstracting and transferring ideas from biology to technical applications in the course of biomimetic projects. For the last couple of years it has appeared that fi ndings achieved during the implementation of functional principles inspired from biology in innovative biomimetic prod-ucts may also contribute to a better understanding of biological systems. This is a relatively new insight of a transfer process that can be referred to as ‘reverse biomimetics’. It can be interpreted as closing the heuristic spiral of technical biology, biomimetics and reverse biomimetics.

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Biomimetics is the realization of technical applications based on insights resulting from fundamental biological research. Biomimetic developments are not direct carry-overs of biology, i.e. never ‘blueprints of nature’. Biomimetics has to be considered as a creative technological implementa-tion. It represents a reinvention inspired by nature. Biomimetic research typically includes several levels of abstraction and modifi cation.

10.3 Benefi ts of natural developments for

technical purposes

Within the disciplines of architecture and engineering, biomimetics is playing a more and more important role in research into lightweight con-structions and technical surfaces. In the development of self-cleaning sur-faces, facade colours like Lotosan® have been established in the market of products for the building industry [8–10].

From the viewpoint of lightweight construction and material optimiza-tion, structurally optimized biomimetic fi bre composite materials like the ‘technical plant stem’ [11–14] are very interesting due to their good mechan-ical behaviour and minimized weight. Tensairity® structures, developed by the Swiss companies Airlight Ltd and Prospective Concept AG, combine pneumatically stabilized membranes (50–300 millibars), compressed steel elements and prestressed cables to make very effi cient ultra-light beams which could be used for different purposes such as roof-beams or even wide-span bridges. Therefore, self-repairing materials for the membranes of pneumatic structures have recently been under development [15, 16].

10.4 Methodology of biomimetics in architecture

and engineering

The methodology of describing processes in biomimetics research that has been developed by the Plant Biomechanics Group Freiburg has proven its effi ciency in projects of the Competence Network Biomimetics, the German Bionics-Competence Network Biokon and the international Competence Network Biokon International, which was established in March 2009.

In the course of research activities, two essentially different approaches have been distinguished, which have been termed the ‘bottom-up’ approach and the ‘top-down’ approach. Depending on the problem to be solved, numerous transitions exist between the two procedures. Within these approaches, there are no clearly defi ned phases after which the biologists’ tasks end or those of the engineers or architects begin. A biomimetic research project generally passes through several iterative loops in order to reach satisfying (interim) results. ‘Pool research’ offers a basic knowledge

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and basic understanding, somewhat like basic research, which can be used by further bottom-up and top-down approaches.

Ideally, both biologists and experts from the technical sector are involved right from the beginning, with varying degrees of importance in each phase of the project. They remain an integral part of the project until a product is introduced onto the market.

10.4.1 ’Bottom-up’ approach in bionics and biomimetics

The starting point for a biomimetic development in the ‘bottom-up’ approach is the research done by the biologist (Fig. 10.1). When this approach is applied, new biomimetic research projects for technical imple-mentation are born from new and promising results of basic biological research.

For expanding these insights and developing them further into innovative market-orientated technical applications, cooperation is required from engineers, technicians and/or architects, which should begin in the early project phases. The sooner biologists and engineers/architects work together in a project, the more accurately they can target their research. Such con-ceptual targeting in the area of biomimetics usually proves to be effective, even during basic research. Interdisciplinary groups of researchers acquire an agreement on their focus while selecting model organisms and methods of analysis.

10.1 ‘Bottom-up’ approach in biomimetics exemplifi ed by the ‘technical plant stem’.

biomechanics,functional morphologyand anatomy

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In the example of a research project of the Plant Biomechanics Group Freiburg and the Institute for Textile and Process Technology in Denkendorf, according to the bottom-up-approach, the fi rst process step is to analyse the biomechanics and functional morphology of a biological system. In the course of analysis, the biomechanics of the entire plant structure and the functional arrangement of plant tissues with various mechanical properties are investigated experimentally. Quantitative analysis then leads in the next step to a thorough principal understanding of the biological structures, shapes and/or functions. Abstraction then follows, i.e., the separation of the principles discovered in the biological model. As long as biological insights have not been made understandable to non-experts in biology, there cannot be a successful implementation in technical applications.

Technical implementation generally takes place fi rstly on a laboratory scale and secondly on an engineering scale, i.e. with methods and produc-tion techniques already established in industry in the same or similar ways. In this phase, production costs and marketing concepts are to be taken into consideration. As industrial development proceeds, biomimetic products are optimized with respect to production sequences and costs and brought to a maturity phase.

10.4.2 ‘Top-down’ approach in biomimetics

The starting point for a biomimetic development in the ‘top-down’ approach is a technical problem (Fig. 10.2). In this case, biomimetic innovations and

search forbiologicalanalogies

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10.2 ‘Top-down’ approach in biomimetics exemplifi ed by the ‘shock absorbing transportation pallet’.

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improvements are sought for already existing technical products that are often quite successful in the market. In the top-down approach, the improve-ment or further development of an existing product is the starting point of the cooperation, i.e., the processing of a concrete technical problem. To increase the chances of success of a biomimetic development, fi rst of all the technical problem and its boundary conditions have to be precisely defi ned.

In the next step, the biologist searches for adaptable natural solutions that can be regarded as analogies to the technical problem. The most prom-ising approaches to a solution are then selected from the usually large number of potential biological example systems and investigated further. For a better understanding, experimental analysis will be performed using the methods of materials science, for example, in order to identify and characterize suitable principles of the biological model that can be applied to the biomimetic product.

As in the bottom-up approach, the next step in the top-down approach is abstraction, i.e., separating the solutions found for the problem in their natural examples, which is again decisive for the success of the entire bionic project. Following a successful transfer of knowledge, it is the task of the engineer to investigate the potential for technical implementation, the tech-nical materials required or the production methods. Biomimetically opti-mized prototypes are produced and the development is extended all the way to industrial production. This is followed by the procedures discussed in the bottom-up approach for further industrial development.

10.4.3 Comparison of bottom-up approach and top-down approach

Two methods of developing biomimetic products can be distinguished according to their process sequences. In actual instances, work can shift from one process to the other as circumstances may require. An example represents the extended top-down approach in which the starting point and the progression of a biomimetic research project is very similar to that described for the ‘regular’ top-down approach (Fig. 10.3). However, in this case the screening for biological concept generators proves that there is a signifi cant lack of fundamental biological data. This leads to one or several iterations of the basic research cycles during the ‘extended’ top-down approach to fi nd the best or at least very good biological templates that can be used as concept generators. To put it simply, in the top-down approach, an engineer or architect contacts a biologist to fi nd out whether nature might have suggestions for solving his particular technical problem. This approach can quickly lead to a successful biomimetic product devel-opment. The apparent limitation here lies in the fact that the innovative leaps which can be expected are usually quite small, since the engineer

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often approaches the biologist with preconceived notions or even with an already (more or less) well-functioning product that he wants to optimize. But since a particular technical problem has only a limited number of effective solutions, the degree of innovation and the number of previously unknown applications is generally quite limited. Conversely, biological functions recognized in the bottom-up approach can often be applied to a very large number of problems if the principle is understood and the abstraction has been successful. The areas of application in this case are not defi ned, but much more open and innovative leaps can be decidedly larger.

Compared to the top-down approach, the bottom-up approach proce-dure requires signifi cantly longer times, often lasting several years, between the recognition of an interesting biological function for technical implemen-tation and the innovative biomimetic product resulting from it [17].

10.4.4 ‘Pool research’ in biomimetics

Architects, designers and civil engineers often use research in biomimetics as a design method or a design tool rather than a research discipline. For them, the wide range of nature’s developments offers opportunities to fi nd new ideas apart from the human-made technical advance. Frei Otto never accepted that he researched in the fi eld of biomimetics. He and his team were interested in natural constructions. They examined the physiology and

search forbiologicalanalogies

identificationof appropriateprinciples

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(higher time need)

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© 2006 Plant Biomechanics Group Freiburg (BIOKON & Competence Network Biomimetics)

10.3 ‘Extended top-down approach’ exemplifi ed by the ‘self-repairing membranes’ for pneumatic Tensairity® structures.

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functionality of animals and plants, often in cooperation with experts on biological topics, e.g. in the research programmes SFB 64 and SFB 230 [1, 2]. But as his Institute of Lightweight Constructions (IL) in Stuttgart infl uenced generations of architects with the so-called announcements, many of them on biological systems, these publications can be seen as one of the fi rst pools to get ideas for tomorrow’s constructions from natural examples.

It has to be seen as a part of the design process for architects, designers and civil engineers to examine natural examples as well as to discover technical possibilities in order to solve a task towards a good solution. This specifi c view on research might not exist in other disciplines, but here it is important to have a pool of understanding nature’s knowledge rather than starting directly with top-down or bottom-up research. Frei Otto’s steps, understanding nature rather than using nature’s examples, are expedient for the present development in architectural biomimetics.

‘Pool research’ may help to analyse promising areas of biology for their suitability for biomimetic developments, as well as to defi ne more precisely the fi eld of study concerning applicability. Extensive tests on the basis of simplifi ed models help to isolate the active principles of natural examples. In this early step of biomimetic research, the results can already be com-pared with those of existing technical solutions. At this point, the potential for a successful transfer to technology becomes evident.

‘Pool research’ is enlarged basic research in the fi eld of biomimetics and allows a broad knowledge base to be created which, using the top-down approach after ‘pool research’, enables a concentration on interesting bio-logical topics right from the start. Using the bottom-up approach, ‘pool research’ helps to discover applicable starting points (see Fig. 10.4).

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10.4 Infl uence of ‘pool research’ on the ‘bottom-up’ and ‘top-down’ approaches.

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The systematic research of the mostly different solutions in nature is, from an application-oriented point of view, the ‘pool’ which is often the basis of the biomimetic work of architects, designers and civil engineers.

10.5 Applications of biomimetics in architecture

Applications of biomimetics in architecture have recently been of increas-ing interest due to the focus on effectiveness in energy consumption and material use and to considerations of durability, recyclability, renewability, CO2 consumption and mobility of architectural constructions [40, 41].

Unless considering the tents of Frei Otto [18–22] or the lightweight con-structions of Richard Buckminster Fuller [23, 24], nor even the early Russian developments of Vladimir G. Suchov [25] or of the Italian engineer Pier Luigi Nervi [26] or the publications of the East German architect Oscar Büttner [27], the technical approaches in architecture and engineering regarding textile constructions or fragile steel constructions have recently been developed more from the state of the art of engineering than from biological knowledge. The constructions of these engineers and architects might, as Frei Otto said, have helped to understand biological functionality. If they did, they widened the fi eld of knowledge in biology, which made natural constructions and functions become interesting for abstracting and transferring new approaches into technical constructions. As the technical point of view very often seems to be limited, and as nature had to solve similar problems during evolution to those faced by architects and engi-neers and has developed several techniques, it is meanwhile seen as an evident method to design architecture with a knowledge base of nature’s functionality.

Some of the new developments of biomimetics in architecture are dis-cussed here. The examples shown will not necessarily be representative and are not able to match all the numerous developments in architecture. In Germany, for example, between manifold research activities in biomimetics, there are research groups in architecture supported by a governmental research programme named ‘BIONA’. The universities that are involved in these research activities are the Technical Universities of Stuttgart and Berlin, the Bauhaus University of Weimar and the University of Applied Sciences of Saarbrücken research group ‘Bowooss’.

10.5.1 The ‘technical plant stem’

The ‘technical plant stem’, as developed by the Plant Biomechanics Group of the University of Freiburg and the Institute for Textile and Process Technology (ITV) in Denkendorf, is described in a separate chapter in this book. It is the result of biomimetic research based upon a great number of structural principles from different plant species. After a comprehensive

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analysis of the mechanical properties of these plants, the physical principles could be determined. In the next step of the development, these principles were abstracted and implemented in the artifi cial product. The hollow profi le was designed to be used also for architectural necessities in a braiding-pultrusion process that is also suitable for continuous industrial production of such products. The structure combines extremely light weight with excellent energy absorption. The innovative biomimetic hollow profi le is highly resilient, considering its weight. Any failure in the composite material due to individual elements separating from the composite (delami-nation) should be further minimized by gradual transitions in stiffness between fi bres and matrix. Here the embedding in a foamed matrix rep-resents one of the numerous possibilities for creating the desired continu-ous transition of stiffness between the stiff fi bres and the more fl exible matrix [11–14, 28, 29].

10.5.2 Wooden tubes

Another example of the use of composites in research into biomimetically inspired structures in architecture are wooden tubes, under development by Prof. Peer Haller at the Technical University Dresden.

Trees are a success model of evolution. Trunks, branches and crotches are best adapted to their environment and their form, function and stability are optimized. In these studies, attempts were made to transfer the mechanical characteristics of trees to architectural applications.

For the production of wooden tubes, Prof. Haller pressed massive panels of wood under heat. The result is a shrinking of the cells. In the next step, the material is steamed and bent in a split cavity to a circular hollow profi le, at which the outer cells expand again. The profi le is fi xed in its form by glueing the ends together. The ends of the tubes can be shaped to be easily stuck into each other.

Maximization of the load-bearing behaviour of these tubes can be achieved by external reinforcement, consisting of composites (see Fig. 10.5). In the experiments a woven fabric of fi breglass, as well as of carbon fi bre, was used, which was laminated with epoxy resin. Static load tests have proved that the new material has signifi cant better characteristics than normal wood, especially if the weight is taken into consideration. Within the areas of connections failures could be observed, which can be avoided by partial fortifi cation of the reinforcement [30, 31].

10.5.3 Self-repairing biomimetic membranes for pneumatic structures

This subject is further studied in an interdisciplinary research project. It targets the development of self-repairing technical materials based on the

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rapid self-repair processes in plants. The research institutions involved are the Plant Biomechanics Group of the University of Freiburg, Germany, the Freiburger Materialforschungszentrum (FMF) and the Center for Synergetic Structures of the Eidgenössische Materialprüfanstalt (EMPA) in Dübendorf, Switzerland. Several species of vines and herbaceous plants capable of quick and effi cient sealing and repairing fi ssures in tissues, caused by inter-nal growth processes or injuries, are used as concept generators for self-repairing biomimetic coatings. The current research results indicate that mainly physico-chemical processes are involved in the early phases of this type of self-repair in vines and herbs.

Biological processes (cell wall biosynthesis, cell growth, cell division) gain in importance during the course of further fi ssure repair. An initial technical implementation is the development of biologically inspired self-repairing membranes for Tensairity® structures. In this innovative technology, load-bearing compression struts and tension cables are kept apart and stabilized by a pneumatic membrane structure under slight internal overpressure (typically 50–300 millibars), thereby creating ultra-light support structures.

The bionic self-repairing coatings prevent or minimize air loss when the membrane is punctured. Compared to uncoated membranes, the rate of pressure loss after puncturing with nails with a diameter of up to 5 mm could be reduced by two to three orders of magnitude by coatings based

10.5 Section of a trunk of fi bre-reinforced wood.

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on biomimetically optimized foams, polymerized under overpressure, thereby achieving an excellent self-repairing effect. In further steps, the self-repairing effect has to be further improved and the durability of self-repairing foams will be tested under various ambient conditions. Moreover, functions should be included in the foams that enable not only sealing of injuries but also the restoration of mechanical properties of the uninjured membrane in the area of the sealed injuries [15, 16, 32].

10.6 Future trends

In spite of the efforts of numerous research institutes dealing with the optimization of lightweight constructions and using a pure engineering approach, recent developments have shown that biologically inspired methods concerning optimization of structures and materials have consid-erable additional potential to improve technical structures [42, 43].

10.6.1 Research on new implementations of biologically functional principles in architectural textiles

During recent years ‘pool research’ has helped to spot a multiplicity of promising beginnings. Almost every possible demand a building should meet has a functioning example in nature. Most of them work on a micro-scopic scale, making textiles the ideal means of implementation, for textiles offer the opportunity of fabricating miniaturized structures.

An example could be the butterfl y’s wing, which provides a powerful lightweight construction. Of particular interest are the colours, which are different from the pigmentations of our technical products. The colours of butterfl y wings do not result from pigments. Responsible for the colourful effects are the structural confi gurations of the surface of the wing that refract the daylight, thus changing the wavelength of the refl ected light. The implementation of this principle in technical products would lead to colours that would never fade or lose their intensity through decreasing pigmenta-tion. This will be a big advance in the development of long-lasting colours [33, p. 139].

The sandfi sh (Scincus scincus) can be cited as a further example whose characteristics could one day be implemented in textile facades. The skin of this reptile, living in the deserts of North Africa, is insensitive to abrasion, which results from the surface structure. It is equipped with tiny minerals, e.g. silicon or calcium crystals, embedded in the keratin. The minerals are arranged wavelike at very small distances apart. Contact with the ground always happens to be by these minerals [33, p. 166]. By implementing this functional principle in architecture, the life expectancy of exterior elements such as facade systems could be considerably increased.

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10.6.2 Hierarchical structures as a strategy of optimization

During their SFB 230 research, Frei Otto’s team were interested in the optimization strategies of the shells of marine plankton, in which analyses of formation of the skeleton were essential. Conjectures on their functions or applications in technical use have been denied. Current scientifi c approaches point to defi ned mechanical purposes and optimization of the mechanical stress capacity regarding the shell structures of diatoms (see Figs 10.6 and 10.7) [34, 35].

PlanktonTech, a virtual institute of the German Helmholtz Foundation under the leadership of the Alfred Wegener Institute for Polar Research, is assembling numerous well-known international partners, such as Harvard University’s Department of Organismic and Evolutionary Biology, Rutgers University’s Institute of Marine and Coastal Science, the University of Freiburg’s Botanical Garden, the University of Kiel’s Zoological Institute, the Technical University of Berlin, ITV Denkendorf’s Department of Bionics and Technical Textiles, and the Lightweight Constructions Institute of Jena. The experts are focusing on basic research and on principles of optimization of lightweight structures of plankton as part of marine life as well as on transfers in textile or fi brous structures of architectural systems. The basic areas of research are shells of diatoms and radiolariae with their outstanding crash resistance and minimal material use. With the aid of modern microscopic methods, shells have been analysed, transferred in 3D

10.6 Diatom of the genus Actinoptychus (source: L. Friedrichs, Alfred Wegener Institute for Polar Research, Bremerhaven).

50.0μm

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data and calculated with the help of different engineering software and optimization tools (see Fig. 10.8) [43].

The team of biologists and the experts in material sciences of natural and artifi cial fi bres and lightweight architecture are trying to transfer knowledge on specifi cally biogenic structures and evolutionary principles into new lightweight technologies as a strategically highly relevant research topic,

100.0μm

10.7 Diatom of the genus Arachnoidiscus (source: L. Friedrichs, Alfred Wegener Institute for Polar Research, Bremerhaven).

10.8 3D analysis of a diatom of the genus Arachnoidiscus (source: Lightweight Constructions Institute, Jena).

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especially as diminishing energy and material resources contrast with an increasing demand for mobility, concerning both people and goods. Technical lightweight structures are typical products of time-extensive developments by engineers who are improving existing technical structures stepwise on the basis of their engineering expertise. Finite element analysis is automated by the bionic optimization procedures of Computer-Aided Optimization (CAO) and Soft Kill Option (SKO), developed by Claus Mattheck at the Karlsruhe Institute of Technology (KIT) [36, 37].

Typically, biogenic materials including biominerals are in fact nano- or micro-composites (see the further 3D analyses in Figs 10.9 and 10.10). Since isotropic materials such as metals are increasingly being replaced by composite materials, the understanding of the effi cient implementation of

10.9 3D analysis of the diatom Coscinodiscus wailesii (source: C. Hamm/J. Geisen, Alfred Wegener Institute for Polar Research, Bremerhaven).

10.10 3D analysis of a diatom shell (source: C. Hamm/C. Kara, Alfred Wegener Institute for Polar Research, Bremerhaven).

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inhomogeneous composites within complex structures is essential for the ultimate optimization of technical lightweight constructions. The manufac-ture and processing of fi bre-based materials – from polymer synthesis, spinning of special fi bres and special fabric formation as well as surface modifi cation and nano-technology up to the manufacture of composites by coating, lamination or resin injection – are of further interest, while imple-mentation possibilities in elements for buildings and architecture are being researched. Production technologies from laboratory-scale dimensions up to industrial production are the focus of realization.

The aim of PlanktonTech is to fi nd the potential for transferring basically biological knowledge to structures for load-bearing or skin-systems for buildings.

Diatoms build hierarchical structures, as can be recognized in Fig. 10.11. The functions of stability are combined with permeability of a certain matter. A fi rst step of transferring the structure of the silicate construction in diatoms to technical fi brous elements is being carried out by ITV Denkendorf in order to examine its usability. First results were shown at the Euro-Composites Fair in 2009 in Stuttgart.

An example of transferring a design application to the roof structure of a new railway station in Luxembourg can be seen in Fig. 10.12. The hierar-chical load-carrying system of the roof shows a hexagonal system of beams, each 15.0 m × 21.0 m. The primary supporting structure is designed to be made of steel tubes. The secondary structure should be supported by a hexagonal system as well, made of triangles formed by a net structure, of size 1.5 × 2.25 m, supported by elements of fi breglass composite in combina-tion with glass. In all these attempts to transfer structure from a microscale to a macroscale, the scaling-up rules strictly have to be taken into consideration.

10.11 Hierarchical structure using a carbon fi bre reinforcement, testing element by ITV Denkendorf.

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10.6.3 Summary – potentials and limitations of biomimetics

For a differentiated view of biomimetics and its methodology, it is necessary to understand the process from its biological basis to the innovative techni-cal implementation. This is the only possible way to present the potential of biomimetics realistically without raising excessively high or false expectations.

Architects, designers and civil engineers often use biomimetics as a design tool and design method rather than as a scientifi c discipline. Research in biomimetics offers a broad knowledge and a pool of ideas towards new developments, which is one of the great tasks in promoting sustainability in architecture and the development of lightweight constructions [40].

Potentials can be found in numerous recent scientifi c publications, notable examples concerning ropes in nature [38], examinations on the simplifi ca-tion of biomechanically inspired structural optimizations [39] and the dis-sertation on bio-inspired skins for buildings [33].


http://www.bionische-innovationen.de/http://www.biokon-international.com/

10.12 Transferring hierarchical structures into a design of a roof structure (source: roof for a railway station in Luxembourg. Julia and Göran Pohl, architects, with Steinmetz et de Meyer, architects, and Knippers Helbig Advanced Engineering, rendering by rendertaxi).

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10.8 References

[1] Brinkman, G. et al. (ed.), 1990. Leicht und weit: zur Konstruktion weitge-spannter Flächentragwerke; Ergebnisse aus dem Sonderforschungsbereich 64 ‘Weitgespannte Flächentragwerke’. Universität Stuttgart/DFG, DT. Forschungsgemeinschaft,VCH, Weinheim.

[2] Teichmann, K. & Wilke, J. (eds), 1996. Prozess und Form natürlicher Konstruktionen: Der Sonderforschungsbereich 230. Berlin: Ernst & Sohn.

[3] Bionics Symposium, 1960. Living Prototypes: the Key to New Technology, 13–15 September, Wadd Technical Report, pp. 60–600.

[4] Nachtigall, W., 2002. Bionik. Heidelberg: Springer. [5] Nachtigall, W., 1997. Vorbild Natur: Bionik-Design für funktionelles Gestalten.

Heidelberg: Springer. [6] Nachtigall, W., 2003. Bau-Bionik: Natur – Analogien – Technik. Heidelberg:

Springer. [7] Nachtigall, W., 2002. Bionik: Grundlagen und Beispiele für Ingenieure und

Naturwissenschaftler. Heidelberg: Springer. [8] Barthlott, W. & Neinhuis, C., 1997. Purity of the sacred lotus or escape from

contamination in biological surfaces, Planta, vol. 202, pp. 1–7. [9] Barthlott, W. & Neinhuis, C., 1998. Lotus-Effekt und Autolack: Die

Selbstreinigung mikrostrukturierter Oberfl ächen, Biologie in unserer Zeit, vol. 28, pp. 314–312.

[10] Cerman, Z., Barthlott, W. & Nieder, J., 2005. Erfi ndungen der Natur: Bionik – Was wir von Pfl anzen und Tieren lernen können. Reinbek, Germany: Rowohlt Verlag.

[11] Milwich, M., Speck, T., Speck, O., Stegmaier, T. & Planck, H., 2006. Biomimetics and technical textiles: solving engineering problems with the help of nature’s wisdom, American Journal of Botany, vol. 93(10), pp. 1295–1305.

[12] Speck, O., Milwich, M., Harder, D. & Speck, T., 2005. Vom biologischen Vorbild zum marktreifen bionischen Produkt: der ‘technische Pfl anzenhalm’. Museo, vol. 22, pp. 96–103.

[13] Speck, T., Harder, D., Milwich, M., Speck, O. & Stegmaier, T., 2006. Bionik: Die Natur als Innovationsquelle. In: P. Knecht (ed.), Technische Textilien, Frankfurt: Deutscher Fachverlag, pp. 83–101.

[14] Speck, T., 1994. Bending stability of plant stems: ontogenetical, ecological, and phylogenetical aspects. Biomimetics, vol. 2(2), pp. 109–128.

[15] Speck, T., Luchsinger, R., Busch, S., Rüggeberg, M. & Speck, O., 2006. Self-healing processes in nature and engineering: self-repairing biomimetic mem-branes for pneumatic structures. In: C.A. Brebbia (ed.), Design and Nature III. Southampton: WIT Press, pp. 105–114.

[16] Speck, O., Luchsinger, R., Busch, S., Rüggeberg, M. & Speck, T., 2006. Self-repairing membranes for pneumatic structures: transferring nature’s solutions into technical applications. In: L. Salmen (ed.), 5th International Plant Biomechanics Conference, Vol. I, Stockholm: STFI Packforsk AB, pp. 115–120.

[17] Speck, T., Harder, D. & Speck, O., 2007. Gradient materials and self-repair: learning technology from biology. VDI-Report, B 4284, pp. 1–13.

[18] Otto, F., 1965. Spanweiten: Ideen und Versuche zum Leichtbau. Berlin: Ullstein Verlag.

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[19] Otto, F. & Rasch, B., 1995. Gestalt fi nden. Stuttgart: Axel Menges.[20] Nerdinger, W. (ed.), 2005. Frei Otto. Das Gesamtwerk: Leicht bauen – natürlich

gestalten. Basel: Birkhäuser.[21] Otto, F., 1982. Natürliche Konstruktionen: Formen und Konstruktionen in Natur

und Technik und Prozesse ihrer Entstehung. Stuttgart: Deutsche Verlags-Anstalt.

[22] Otto, F., 1992. Natürliche Konstruktionen. In: Universität Stuttgart & Universität Tübingen Veröffentlichungen des Internationalen Symposium des SFB 230, Natürliche Konstruktionen – Leichtbau in Architektur und Natur.

[23] Krausse, J. & Lichtenstein, C., 2001. Richard Buckminster Fuller: Your Private Sky – Design als Kunst einer Wissenschaft. Baden: Verlag Lars Müller.

[24] Edmondson, A.C., 1987. A Fuller Explanation: The Synergetic Geometry of R. Buckminster Fuller. Basel: Birkhäuser.

[25] Graefe, R. (ed.), 1990. Vladimir Grigorevic Suchov: Die Kunst der sparsamen Konstruktion. Stuttgart: Deutsche Verlags-Anstalt.

[26] Greco, C., 2008. Pier Luigi Nervi: Von den ersten Patenten bis zur Ausstellungshalle in Turin 1917 – 1948. Luzern: Quart Verlag.

[27] Büttner, O. & Hampe, E., 1977. Bauwerk – Tragwerk – Tragstruktur, Vol. 1+2. Berlin: VEB Verlag für Bauwesen; Teufen: Arthur Niggli.

[28] Milwich, M., Planck, H., Speck, T. & Speck, O., 2007. The technical plant stem: a biomimetically inspired narrow fabric. Melliand – Narrow Fabric and Braiding Industry, vol. 44(2), pp. 34–38.

[29] Rüggeberg, M., Burgert, I. & Speck, T., 2006. Fibre–matrix interfaces in plants as model systems for technical composites. In: L. Salmen (ed.), 5th International Plant Biomechanics Conference, Vol. I, Stockholm: STFI Packforsk AB, pp. 77–82.

[30] Hartig, J., Lepenies, I., Haller, P. & Zastrau, B.W., 2009. Baukonstruktionen aus der Natur: neue Techniken im Umgang mit natürlichen Wuchsformen. In: 9th Holzbauforum Leipzig, pp. 1–10.

[31] Haller, P., 2009. Von Fasern und Fäden: Konzepte für textile Bewehrungen in der Holzkonstruktion. In: Schweizerische Arbeitsgemeinschaft für Holzforschung SAH (ed.), Holzforschung Schweiz, vol. 1, pp. 10–17.

[32] Busch, S., Speck, T., Liszkay, A., Speck, O. & Luchsinger, R., 2006. Self-repair processes in plants as concept generators for innovative biomimetic technical materials with self-repairing functions. In: L. Salmen (ed.), 5th International Plant Biomechanics Conference, Vol. I, Stockholm: STFI Packforsk AB, pp. 83–88.

[33] Braun, D.H., 2008. Bionisch inspirierte Gebäudehüllen. PhD thesis, Stuttgart: Universität Stuttgart.

[34] Hamm-Dubischar, C., 2005. Kieselalgen als Muster für Technische Konstruktionen. BIOspektrum, 1/05 (11), pp. 41–43.

[35] Hamm, C.E., Merkel, R., Springer, O., Jurkojc, P., Maier, C., Prechtel, K. & Smetacek, V., 2003. Architecture and material properties of diatom shells provide effi cient mechanical protection. Nature, vol. 421, pp. 841–843.

[36] Mattheck, C., 1997. Design in der Natur: der Baum als Lehrmeister, 3rd edn, Freiburg: Rombach Verlag.

[37] Mattheck, C., 2006. Verborgene Gestaltgesetze der Natur: Optimalformen ohne Computer. Karlsruhe: Forschungszentrum Karlsruhe.

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[38] Kappel, R., 2007. Zugseile in der Natur. In: Forschungszentrum Karlsruhe in der Helmholtz-Gesellschaft (ed.), Wissenschaftliche Berichte FZKA 7313.

[39] Sauer, A., 2008. Untersuchungen zur Vereinfachung biomechanisch inspirierter Strukturoptimierungen. In: Forschungszentrum Karlsruhe in der Helmholtz- Gesellschaft (ed.), Wissenschaftliche Berichte FZKA 7406.

[40] Pohl, G., 2006. Konstruktive Architektur: Leicht und Weit. In: B. Baier (ed.), Reichweiten – Leichte Konstruktionen. 5. Interdiszipläres Symposium Essen für konstruktive Gestaltung. Verlag der Universität Duisburg-Essen, pp. 69–93.

[41] Pohl, G., 2006. In: K.G. Blüchel, F. Malik, SWR & Das Erste, Faszination Bionik: Die Intelligenz der Schöpfung. Verlag Bionik Media GmbH.

[42] Pohl, G., 2007. Industriespionage bei Mutter Natur. In: Politische Ökologie: Nachhaltiges Design – Laboratorium für industrielle Neuanfänge, 105, Oekom Verlag.

[43] Pohl, G., 2009. Konstruktionsprinzip Effi zienz – effi ciency as a construction principle. In: VDI-Symposium on Innovative Building Materials, VDI-Verlag.

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11Smart textile and polymer fi bres for

structural health monitoring

A. GÜEMES, Universidad Politecnica de Madrid, Spain and T. B. MESSERVEY, D’Appolonia S.p.A., Italy

Abstract: Structural health monitoring (SHM) is an emerging technology, aiming to afford to the structure a capability for load monitoring and for damage detection. This is done by attaching permanently to the structure a sensor network, accompanied by a data processing system. Among existing sensors, those based on fi bre optics are described in detail. Easily integrated into textiles, these sensor-embedded systems have specifi c potential for the construction industry.

Key words: fi bre optic sensors (FOS), strain monitoring, damage detection, textiles.

11.1 Introduction: concept of structural health

monitoring (SHM)

Structural health monitoring (SHM) is the result of the integration with the structure of a network of sensors, whose response is collected and processed almost continuously. An effi cient signal processing technique is needed to process the raw sensor measurements and draw from them an estimate of the damage size and location, being able to distinguish the damage from other perturbations caused by environmental disturbances. The system should automatically generate warning alarms when there is a structural risk, or when maintenance is required.

SHM includes two lines of action, load monitoring and damage detection, with different procedures but complementary in their application. Load monitoring is usually done by measuring the strains at some critical points at the structure, to detect any overload; it is also used to calculate the fatigue accumulated by the structure and for prognosis of the remaining life of the structure. Damage detection aims to detect any unexpected crack appearing somewhere in the structure.

SHM systems have been in service since 1990, and perhaps even earlier. One of the most successful examples of implementation of SHM concepts started with helicopters servicing offshore oil platforms. The integration of some sensors (accelerometers) in the mechanical drive train, along with

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Smart textile and polymer fi bres for structural health monitoring 331


a sophisticated analysis of the harmonic content, allowed for an early detection of any malfunction, reducing the number of incidents and acci-dents. Specialized commercial systems are currently available for this purpose, and these systems are now required by the regulations of most countries.

Conventional structures, such as a bridge or a civil aircraft, are still commonly passive structures. These structures are designed to withstand the maximum expected loads, even in the presence of small cracks that may occur in service, due to corrosion, impacts with external objects or any other reason. The maximum crack size before catastrophic failure can be predicted, and the detectable crack size (of course, much smaller than the critical size), are defi ned according to the available non-destructive methods; also the crack growth by dynamic loads can be predicted. Therefore, the time between inspections can be defi ned to avoid any incipi-ent but undetected crack to become critical. This is the so called ‘main-tenance on schedule’, and it has proven to be a very safe method – presently the percentage of aircraft accidents due to structural failure is very low. But the cost of these inspections is high, because they require sophisticated NDI and many labour hours. The cost of maintenance is about a quarter of the total life-cycle costs of an aircraft, similar to the fuel, crew, or acquisition costs.

The immediate goal of SHM for civil applications is to reduce these operating costs without compromising safety. One main difference with respect to the NDE is that the sensors are permanently attached to the structure, so there is no need for disassembly and inspections can be done almost continuously without cost. These systems must remain operational throughout the life of the structure. Still under development, when fully available and reliable, SHM systems will reduce the time and maintenance costs by eliminating unnecessary checks and replacements (Frangopol and Messervey, 2009). Textbooks on the application of fi bre optic sensors to civil infrastructure are just beginning to emerge. One such excellent reference is provided by Glisic and Inaudi (2007).

11.1.1 Load monitoring

Load monitoring is very important for military aircraft. The life of an air-craft structure is limited by the material fatigue due to dynamic loads, and therefore is related to the severity of the manoeuvres performed by the pilot. Fatigue management means the rotation of aircraft to obtain a uniform ageing of the fl eet, and it has important economic consequences. Sensor technology for measuring the local strains, with capability for long-term duration, is already available and has been demonstrated in aeronautical structures and also at high-responsibility bridges. Most of this chapter will

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address the technology for carrying this out, so the details will be discussed later.

11.1.2 Damage detection

The applicability of the techniques for the detection of damage depends on the type of structure, the type of loads, and the maximum allowed crack size. The simplest case is the automatic detection of damage in rotating machinery, now a commercial technology called ‘condition monitoring’, based on the analysis of the changes that the damage produces in the dynamic response of the machine, or in its spectral response. But these techniques cannot be extrapolated to other types of static structures such as bridges, aircraft, power plants or many high-responsibility structures. The following paragraph discusses the current state of the art, with their needs, options and constraints.

Four levels of damage identifi cation are defi ned, as follows:

• Level 1: Determination that damage is present in the structure• Level 2: Determination of the geometric location of the damage• Level 3: Quantifying the severity of damage• Level 4: Predicting the remaining useful life of the structure.

Currently the best developed damage detection techniques are those methods based on vibrations, with signifi cant demonstrations in the fi eld of civil engineering. Vibration-based identifi cation techniques use the changes promoted by damage at the modal frequencies and/or mode shapes of the structure obtained by dynamic tests. Different approaches have been identi-fi ed in the literature; a review was given by Sohn et al. (2003).

Unfortunately, the crack size required to obtain a clear indication of damage by vibration methods is too large compared to the maximum size allowed for aircraft structures, so these methods were not applicable for these kind of shell structures.

For thin shell structures, the most promising methods are those based in the analysis of the propagation of elastic waves. The wave propagation methods have often used piezoelectric wafer active sensors (PWAS) as transmitters to generate waves and simultaneously as receivers to measure the echo signals due to the defects. A time-frequency analysis allows an estimation of crack size on the basis of the relationship between new and baseline response. The sensitivity of Lamb waves to defects depends largely on the frequency, and for complex structures the dispersive Lamb waves interact with reinforcements with partial refl ections and refractions. These systems have not reached the level of maturity required for industrial appli-cations. A full discussion with alternatives is presented in the book by Giurgiutiu (2008).

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11.2 Smart fi bres for structural health

monitoring (SHM)

Measures (1989) spoke about ‘structures with nerves of glass’, and this article must be considered at a starting point for ‘smart structures’. Optical fi bres have the main quality of transmitting the light (information), but sensors can be engraved on them at specifi c points, modulating the optical signal in response to an external action, like temperature or strain, and becoming a sensor for it. As optical fi bres are easily embedded into the materials, the analogy to nerves is fully justifi ed.

11.2.1 Nature and principles of optical fi bres

Optical fi bres, or fi bre optics as they are commonly referred to, are tiny strands of glass with a diameter about 0.2 mm, on the same order of mag-nitude as a human hair. They are surprisingly more fl exible and robust than one would think for glass. Optical fi bres (OF) are cylindrical dielectric waveguides for the transmission of light, made from high purity, low loss optical material, usually silica, but plastic and other materials are also com-mercially available. The refractive index (around 1.46 for silica) at the central axis or ‘core’ is slightly higher than that of the surrounding material or ‘cladding’, due to the presence of dopants. Internal optical rays travelling nearly parallel to the axis reach this interface with an angle exceeding the angle for total refl ection defi ned by Snell’s law, so they continue to be con-fi ned at the core. Only when the fi bre is bent with a strong local radius does the light escape. The OF is externally protected from scratches with a mechanical plastic coating (the ‘buffer’), and often several optical fi bres are bundled together, and assembled with high-strength fi bres such as Kevlar, to make a robust product known as optical cable that can withstand indus-trial handling.

A minimal knowledge of the physics of light is needed to understand the optical fi bre sensors. Light is just a small part of the spectrum of electromagnetic radiation. The nature of this radiation can be viewed as photons or waves that travel at the speed of light, c, which is around 300,000 km/s. Different theories of increasing complexity have been pro-posed to explain the nature of light (Saleh, 2007). The simplest model, known as ray optics, states that light goes through the minimum time path (Fermat’s principle). The speed of light is c/n, where n is the refrac-tive index. It explains the refl ection and refraction phenomena. Huygens proposed the theory of ‘scalar waves’, which also explains the phenom-enon of diffraction. Maxwell considered light as electromagnetic waves (vectorial waves), giving an explanation for polarization. The more complex models, based on the Schrodinger equations, are known as quantum

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optics. They are needed to explain the exchange of energy between matter and radiation. Fortunately, they are not needed to work with optical sensors.

The external diameter of the optical fi bres used to be 125 microns without buffer, and 250 microns with the standard acrylate protection. Optical fi bres are now classifi ed into two main groups: single-mode (core diameter about 10 microns) and multi-mode (core diameter 30 to 100 microns). Single-mode OF offer some advantages for optical communications, such as a smaller optical attenuation, because of the smaller difference between the refractive index of core and cladding, which requires a lower concentration of dopants. Multi-mode fi bres distort the group signal due to the dispersion of individual modes travelling at different speeds. As an advantage, the larger core allows easier alignment with the optical sources and connectors. They are preferred when used only as light guides, as in many medical applications. When used for sensing purposes, they may only be used for intensity-based methods.

Optical power losses are very small, about 0.03 dB/km. This means that over 100 kilometres the optical power is halved; this is an important requirement for telecommunications. Optical power loss is minimized near the wavelengths of 1300 nm and 1550 nm, where the minimum Rayleigh scattering or minimal infrared absorption is found. For sensing purposes, the losses in the fi bre optics are irrelevant, but still 1550 nm is the pre-ferred window, since the optoelectronic components are more readily available.

11.2.2 Types of fi bre optic sensors

This discussion is mainly limited to measurements of temperatures and strains, but fi bre optic sensors are used in many other applications, as chemical sensors, electrical fi elds, etc. A global review can be found in Lopez-Higuera (2002).

Common benefi ts of all types of fi bre optic sensors stem from their small size and weight, and their non-electrical nature, which makes them immune to EM interference and electrical noise, while also allowing them to work in explosive environments. In general terms, fi bre optic sensors (FOS) have a high sensitivity and a wide operating temperature range. Multiplexing capability, or the possibility to ‘write’ several sensors in the same optical fi bre, is another highly desired feature.

A sensor is a device capable of converting a physical or chemical quantity into readable information. In addition to a topological classifi cation (local or distributed, intrinsic or extrinsic), a more basic classifi cation can be made according to the optical parameter affected by the external factor: intensity, phase, wavelength, and polarization.

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Intensity sensors

These devices are the simplest sensors among FOS, and consequently the fi rst to be implemented, and they are still in use as sensors for proximity, damage detection by fi bre break, and monitoring the curing of composite materials. The sensing system consists of a stable light source, an optical fi bre, preferably of the multi-mode type for higher power transmission, and a photo detector (Fig. 11.1). Microbending sensors were popular intrinsic sensors for pressure monitoring, based on intensity measurements (Fig. 11.2). It is known that light is kept inside the optical fi bre because its angle of incidence is smaller than the angle of critical refl ection at the core–cladding interface, which is always true except at sharp bends. If the OF is placed between two rough surfaces, increasing pressure promotes greater bending, thus increasing the optical losses. Early studies were done with this concept, now nearly abandoned because of diffi culties of calibration; optical power fl uctuations in the light source, connectors, temperature, etc., cause the accuracy of the system to be rather low. However, this phenom-ena has to be remembered, particularly when working with fabrics and

11.1 Sketch of fi bre optic system.

Light source

Photodetector

Isolator Connector

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controller

Splice Multiplexer

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Micro-bending losses

Output

Fibre optic

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Input

Perturbation

11.2 Microbending sensor.

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textile composites; microbending losses promoted by the texture in textile composites can fade out the optical signal. Before making any attempt to include the OF into the fabric (as, for example, for RTM), the fi bre must previously have been protected against microbending.

Phase modulation as optical fi bre sensors, or interferometers

Interferometry is the most accurate laboratory technique for precise mea-surement of distance. It should be recognized that direct measurement of the phase of an electromagnetic wave cannot be done for the optical wave-lengths, as is done with oscilloscopes for low-frequency electrical signals, and only the light intensity, which is the average power of the electromag-netic fi eld, can be measured with photodetectors.

Interferometers are the way to extract information about the phase from intensity measurements (Fig. 11.3, showing a sketch of a Mach-Zender interferometer). A monochromatic (single-frequency) light wave is split into two beams (either with a partial mirror in conventional optics or with a coupler in the case of optical fi bres), then these waves travel through dif-ferent paths before being recombined; a difference in path length of half a wavelength (380 nanometres when the red light of a He-Ne laser was used) will cause a delay of one wave to another and, consequently, their electro-magnetic fi elds will sum in opposition, and the intensity at output will be zero. The interferometer signal will move from the input power level to zero, as outlined in Fig. 11.4, when the length of either of the two arms increases or decreases in half the wavelength. If the experiment is carried out with care, changes in the length of the order of 10 nanometres can be detected. This extreme sensitivity to any disturbance in the optical path of either of the two arms makes it diffi cult to do measurements outside the laboratory environment; a change in temperature can cause several maximum and minimum drifts.

Other common architectures for interferometric optical fi bre systems are known as Mach-Zender, Michelson and Fabry-Perot, the names coming

Reference fibre

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z1

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Sensing

fibre

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detector

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U2

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11.3 Mach-Zender interferometer.

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from classical optical interferometry. In the Michelson and Fabry-Perot systems, light is refl ected at the end of optical fi bres, travelling back and recombining again. Fabry-Perot is special in the sense that light travels most of the time by a single fi bre; the interference is created between the waves refl ected in a partial internal mirror and the waves that pass through the mirror and are refl ected later. A detailed review of each of these systems is found in the literature. For smart structures, a single optical fi bre is pre-ferred because only one ingress point into the structure is needed. Extrinsic Fabry-Perot heads, known as ‘microcavities’, are commercially available; a precision wafer is bonded to the end of the fi bre, leaving a small gap, working as miniature pressure sensors.

Sensors based on wavelength, or Bragg gratings

This is a kind of local, intrinsic, absolute, multiplexable, interrupt-immune fi bre optic strain sensor, on which attention has been focused since its dis-covery in the early 1990s. The basic idea is to permanently engrave, at the core of the fi bre and for a short distance (about 1 cm), a periodic modula-tion of the refractive index. This behaves as a series of weakly uniformly spaced mirrors, causing a diffraction of incident light, refl ecting the wave-length which is exactly proportional to this spacing and to the refractive index. The Bragg grating acts as a very narrow optical fi lter, as shown in Fig. 11.5. For a broadband light pulse travelling through the fi bre, when arriving at the FBG most of the light goes through, except a single fre-quency which is refl ected back. If the grating is subjected to a uniform axial strain, or a temperature change, the peak of the refl ected wavelength moves due to changes in the spacing and refractive index. Any optical spectrum analyser (OSA) will be able to detect these changes and turn them into readable information. Commercially available sources of white light have

0 5 10 15 20 25

Phase (rad)

Power

output,

I

Imax

Imin

11.4 Power output from an interferometer sensor.

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a spectral width of about 40 to 60 nanometres; the maximum drifting by temperature or strain is about 5 nm, so several Bragg gratings centred at different wavelengths can be written in the same optical fi bre and inter-rogated at the same time. Multiplexation is then easily implemented. The fact that information is encoded in the wavelength makes the sensor very stable to ageing, which allows measurements of strains during long periods without recalibration.

11.2.3 Response of fi bre Bragg grating (FBG) to strain and temperature

Fibre Bragg gratings have a measuring range capability for axial strain up to 10,000 microstrains (1%) and for temperatures from cryogenic condi-tions to 600°C. The relative shift in the Bragg wavelength, ΔλB/λB, due to an applied strain ε and a change in temperature ΔT is given by:

ΔλB/λB = CS ε + (αΛ + αn) ΔT

Here, CS is the coeffi cient of strain, which is related to the strain optic coef-fi cient Pe. The coeffi cient of temperature is made up of the thermal expan-sion coeffi cient of the optical fi bre, αΛ, and the thermo-optic coeffi cient, αn. These parameters are slightly dependent on the FBG manufacturer, but typical values are 0.79 for CS, and 0.55E − 6 and 8.6E − 6 for αΛ and αn respectively.

Coupler 2×1

LED

Light source

Optical spectrum analyser

λ1 λ2 λ3

11.5 FBG basic principle for strain and temperature sensing.

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Experimental results show that wavelength drifting is very linear with strain at any temperature. Wavelength drifting with temperature deviates from linearity at extreme temperatures; in fact, under cryogenic conditions the linearity is lost, as seen in Fig. 11.6. At liquid helium temperature (4.2 K) both coeffi cients are almost zero and the wavelength with the temperature variation is negligible in these conditions.

11.2.4 FBG interrogation systems, characteristics and performance

The global sketch of the interrogation system to detect wavelength drifting was represented in Fig. 11.4. The radiation coming from a light source, which can be either a broadband light emitting diode (LED) or a tunable laser, then goes through the coupler, and then is launched into the sensing fi bre. Some wavelengths are refl ected back at the FBGs, and the coupler drives this radiation to some device able to distinguish the wavelength, like a tunable fi lter, and then to a photo-detector.

The characteristics that defi ne the performance of the interrogator are:

• Operating wavelength and range. Usually centred at 1550 nm, the range defi nes the number of FBGs that may be engraved at the same optical fi bre. There are also commercial systems at 850 nm.

• Scan frequency. Ability to track dynamic strains. Standard systems work up to 1 kHz, which is enough for most mechanical vibration phenomena; special systems may attain 500 kHz, needed to track impacts or elastic

Temperature (K)

Wavele

ngth

(nm

)

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11.6 Wavelength drifting in cryogenic conditions.

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waves in solids. Quasi-static systems are used when information about the full spectrum, and not only the peak wavelengths, is required.

• Accuracy. Typical accuracy is about 1 pm, equivalent to 0.7 microstrains, or 0.1°C (when working at a central wavelength of 1550 nm).

• Number of channels. Number of optical fi bres that may be connected to the equipment without a multiplexer.

11.3 Smart composites

Although the fi bre optic, and therefore the sensors, can be bonded externally to any material on any structure, the concept of smart structure carries inherently the concept of integration. Advantages associated with embedding fi bre optic sensors are:

• The optical fi bre and sensors, intrinsically brittle, will be protected by the structure.

• The existence of an intimate sensor/host union, ensuring that the strains experienced by the sensors are the same as the strain existing in the structure.

• The absence of external wiring, important not only from the aesthetic point of view, but also allowing the use of fi bre optic sensors for applica-tions that require clean surfaces, as in aeronautical structures.

• The possibility for internal monitoring of the structure, in places which cannot be reached by conventional sensors, or where sensors would be too intrusive because of their size and the high number of wires that are usually necessary to route them.

A full integration of sensors into the host material is limited by the manufacturing processes, being necessary to avoid potentially aggressive operations, such as high pressure, shear stresses and very small chamfers. For example, the maximum temperature for silica fi bre is about 800°C, limiting the possibility for embedding it into molten metals and metal matrix composites. Concrete structures and advanced composite materials with a polymeric matrix are more adequate for integration purposes. Figure 11.7 shows a polymer composite ‘smart patch’ with embedded FBG sensors affi xed to an RC beam for laboratory testing. Although this specifi c patch is intended for monitoring only, the inclusion of stiffer composite materials can be realized to obtain the functionality of reinforcement, repair, or strengthening.

A critical factor is the ingress/egress of fi bre optics to/from the structural material. Connector systems developed by the optical fi bre communications industry are available, but they are very bulky for being embedded into composite structures without causing signifi cant deterioration of the struc-tural strength, or endangering the structural integrity. A commonly adopted

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solution is to protect the OF inside Tefl on tubing, which is also embedded 2–3 cm inside the laminate. Nevertheless, the solution is not robust enough, and embeddable miniature connectors are still being investigated. Another promising technique under investigation is the development of stand-off interrogation using free-space optical porting techniques as reported in m Teitelbaum et al. (2008). In this work, the embedded ends of fi bre optic cables are cut at a 45° angle, polished, and glazed to achieve a mirror effect. A guiding indentation is used to align a stand-off light source which hits the mirror, travels the length of the fi bre optic cable, and can be read on the other end or sent back using a separate mirror at the far end of the cable. In the future, such techniques could eliminate the need for bulky connector systems and non-robust interfaces.

11.3.1 Microbending and other issues for embedded sensors

Three phenomena may complicate the response of embedded FBGs, par-ticularly when the optical fi bre is embedded inside a composite made from fabrics prepregs. These issues are:

• Microbending• Strain gradients along the grating• Transverse stresses on the grating.

The fabrics are made by crossing thick tows of glass or graphite fi bres; these tows are undulating, as can be seen in any cross-section. Any attempt to include an optical fi bre inside the tow will cause a continuous bending of the OF, with large optical losses; the optical signal will be lost in less than 50 cm. Even when the OF is located at the surface of the fabric, if squeezed

11.7 Sensor-embedded composite ‘smart patch’ on a RC beam (courtesy of APC Composite, Sweden, and Safi bra, Czech Republic).

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between two fabrics the surface roughness will promote microbending and optical losses. A common approach to solve this issue is either to use a thick protective coating of the OF, or to locate the optical fi bre inside a prepreg tape (tapes are made commercially with bundles of parallel structural fi bres), so microbending is avoided.

The main mission of the coating is the mechanical and environmental protection of the OF. Commonly used materials for coating optical fi bre are polymers, either acrylate or polyimide. Standard optical fi bre is protected with an acrylate coating (about 50 microns in thickness, so the total diam-eter of the OF will be 250 microns), with a low elastic modulus and strength, which oxidizes at the temperatures used for curing composite materials (around 180°C). This coating is easy to remove, either mechanically or with solvents. Polyimide has a higher stiffness, and does not degrade at these temperatures, which is why it is preferred for embedding in composite materials; this PI layer is thin, the total diameter of the OF used being 150 microns.

11.3.2 Response of the FBG to uniaxial tension, non-uniform fi eld

Figure 11.8 shows the spectrum of a standard FBG, as a very narrow (0.1 nm) symmetric Gaussian peak. This spectrum can be acquired by an OSA (optical spectrum analyser), representing the refl ected power inten-sity as a function of the wavelength. The peak simply moves forward or backward when the FBG is stressed uniformly. If the FBG is subjected to two different strain levels along its length, two peaks of reduced height should be expected. In general terms, a strain gradient along its length will

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1320 1322 1324 1326 1328 1330 1332 1334

Wavelength (nm)

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11.8 Peak drifting under uniaxial strain.

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distort the refl ected peak, as seen in Fig. 11.9. The direct problem, to calcu-late the shape of the refl ected peak by an arbitrary strain fi eld, can be easily solved by transfer matrix formalism (TMF). This is a numerical method to solve the equations for coupled mode aperiodic grating structures. The inverse problem is mathematically very complex, does not have a unique solution, and has very little practical interest; instead of making a long FBG and analysing its distorted spectrum, it is easier and more accurate to engrave several shorter FBGs, closely spaced.

The strain gradients may greatly complicate the response of FBGs bonded in composite structures made from fabric prepregs, as shown in Fig. 11.9. FBGs bonded on the surface of a woven laminate will experience a strong spectral distortion under loads, due to local strain changes at the tows coming from the warp or weft directions. The way to solve this problem is either to make a quite small FBG, about 1 mm in length, which implies a wider peak and lower resolution, or to cover the FBG with a stiff coating that averages the strain fi eld. The same problem arises for an FBG bonded to concrete with coarse sand and stones. This is always an issue that may be solved, as far as users are conscious of it, but spectrum analysers are needed for it. Standard FBG interrogation systems, which only look for the peak drifting, will give wrong information about the strain fi eld.

11.3.3 Response of the FBG to transverse stresses

A stress fi eld applied transversely to the grating modifi es the structure of the previously isotropic optical fi bre, generating two perpendicular direc-tions with different indices of refraction. For a single Bragg grating spacing

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1297.5 1298 1298.5 1299 1299.5 1300 1300.5 1301 1301.5

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11.9 Peak distortion by strain gradients, as happens in textile composites.

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there will be two wavelengths that verify the Bragg condition, and the optical spectrum of the grating is split in two peaks (Fig. 11.10). These transverse stresses always appear in general laminates cured at high tem-peratures, and are known as residual stresses. Consequently, embedded FBGs show two peaks, instead of a single one. The distance between the two peaks is proportional to the transverse stress at the fi bre core, but this fact is not useful, because the local transverse stresses at the core are dif-fi cult to predict and correlate with the average transverse stresses, by the infl uence of the coating; both peaks move simultaneously when longitudi-nally strained. The best procedure is to avoid or minimize these transverse stresses by using a thick coating on the FBG.

11.4 Future trends

11.4.1 Highly multiplexed systems

While there are other multiplexing/demultiplexing schemes, the two most common are time division multiplexing (TDM) and wavelength division multiplexing (WDM).

Time division multiplexing uses the fact that light takes a fi nite time to travel the distance from the source to the FBG and back. This time increases as the distance between the FBG and the source increases. Each FBG is positioned at a different (known) distance from the sensing unit. The optical source sends a quick burst of light and the returning signals are recorded. The burst of light must be short enough so that it is not still on when the signals are returning. The returned signals are identifi ed by the time that they arrive at the sensing unit; naturally the FBGs that

1.0E-10

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1322.0 1322.5 1323.0 1323.5 1324.0

λ (nm)

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11.10 Peak splitting by transverse stresses.

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are farther away will return later than those that are closer. As one can imagine, this requires an extremely short pulse of light. The FBGs must be placed at least 1 m apart for TDM to be practical. Due to the depen-dence on time, TDM is generally limited to static measurements. This method has one distinct advantage over WDM in that all the FBGs may operate in the same wavelength band. This allows for more FBGs to be multiplexed, though more FBGs result in slower readings if all sensors are read at once.

Wavelength division multiplexing relies on the fact that the Bragg wave-length band that each FBG operates on is different. This method has the advantage over TDM in that it operates in real time and the frequency of reading is only dependent on the equipment used. A disadvantage over TDM is that every FBG in the same OF must have a different wavelength, adequately spaced to ensure that there is no wavelength overlap. The light source can be broadband, although the trend towards fast sweeping lasers is becoming more common. A fast sweeping laser can supply more power, resulting in a longer range, and can supply a larger wavelength source (from 50 to 100 nm wide).

11.4.2 Distributed sensing systems

This is really a unique property attainable with fi bre optics – the possibility of sensing all along the hundreds of metres of fi bre, giving the temperature and strain at each point. Distributed strain sensing is the most recent tech-nology, and commercial systems have been available only in recent years. They are still limited to static measurements, but their accuracy in reading the position and strain is getting comparable to that obtained with a highly multiplexed system.

The start point of fi bre optic distributed sensing may be identifi ed at the beginning of the 1980s, with the optical time-domain refl ectometer (OTDR) technology, a technique widely used for telecommunication optical cable testing. The concept is to send a narrow pulse of light through the optical fi bre, and keep hearing the ‘echo’ of the backscattered radia-tion. Any local defect will cause a surplus on the backscattered radiation; the location of the defect may be calculated by the ‘time of fl ight’. Resolution is in the order of metres, but the operating range was several kilometres, so the technique has been found very useful in locating fi bre breaks.

Because the velocity of light propagation in the optical fi bre is well known, the distance can be determined from the time of fl ight of the returning backscattered light. The backscattered light consists of different spectral components due to different interaction mechanisms between the propagating light pulse and the optical fi bre. These backscattered

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spectral components include Rayleigh, Brillouin, and Raman peaks or bands. The Rayleigh backscattering component is the strongest one, due to density and composition fl uctuations, and has nearly the same wave-length as the primary laser pulse. The Rayleigh component controls the main slope of the intensity decay curve and may be used to identify the breaks and heterogeneities along the fi bre. OBR systems use this back-scattered radiation to get information about the strain and temperature at each point, with surprisingly good resolution, but still they are very expensive.

A small percentage of photons interchange energy with the atoms and new photons with smaller (Stokes components) or higher energy are pro-duced. This is known as Raman scattering; the spectral shift is related to the frequency of the atomic oscillations. The intensity of the anti-Stokes component of the Raman radiation increases with temperature, while the Stokes component remains stable; the ratio of power of these two peaks, together with the time of arrival, affords information about the local tem-perature and position, respectively. Some commercial systems are currently available to get temperature maps over long distances, with important hydrologic and environmental applications, including the detection of leak-ages in buried pipes.

Brillouin scattering occurs as a result of an interaction between the propagating optical signal and thermally acoustic waves present in the silica fi bre giving rise to frequency-shifted components, similar to a Doppler effect. The acoustic velocity is directly related to the medium density and depends on both temperature and strain. As a result, the so-called Brillouin frequency shift carries information about the local temperature and strain of the fi bre. Furthermore, Brillouin-based sensing techniques rely on the measurement of a frequency as opposed to Raman-based techniques that are intensity based.

11.5 Smart textiles

Textiles offer an effi cient and effective way to integrate fi bre optic systems with a host structure. For specifi c geotechnical and masonry applications, such textiles are already being utilized in the construction industry. Making such textiles sensor-embedded is a logical progression of the state of the art and will provide engineers with an additional tool to collect monitoring information. Such tools are also acutely needed in the retrofi t of monu-ments and historical structures in areas of cultural heritage (Casciati and Faravelli, 2009). The development of such textiles for these purposes is being conducted in the FP7 EC partially funded research project ‘Polyfunctional Technical Textiles Against Natural Hazards (POLYTECT)’, www.polytect.net, from which this section is developed.

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11.5.1 Manufacture

In general, fi bre optic sensors can be either sewn onto or warp-knitted directly into textile structures. For applications where the sensor is sewn onto the textile, a 3D rope-like structure is typically made with the sensor at the core and outer fi bres that protect and transfer stresses to the sensor. Warp-knitted applications are generally thought of as 2D because they are intended for area coverage. For these textiles, sensor protection is offered by a polymer coating, a robust sensor casing, or its integration into compos-ite or mortar construction. The incorporation of fi bre optic sensors (as fi la-ment feed material) requires slight modifi cations to the machinery to guide and protect the sensor as well as to not cause damage to the equipment itself.

11.5.2 Types of products and their applications

Figure 11.11 shows several types of sensor-embedded textiles for geotechni-cal and masonry applications. Matching the appropriate product to a spe-cifi c application is determined primarily by the type of measurement desired. For geotechnical applications, static distributed measurements are most attractive. Using OTDR, measurement ranges in the hundreds of metres are possible at a cost of a few euros per metre with an acquisition time of a few minutes. A complete report on this system is provided by Liehr et al. (2009). Using Brillouin scattering, measurement ranges up to 20 km are possible at a cost of tens of euros per metre with a signal acquisi-tion time between 20 and 30 minutes. These parameters are rough approxi-mations and are evolving with the state of the art. Geotechnical applications include embankments, slope stability areas of concern, dykes, levees, foun-dations, road construction, and landfi lls. Typically, the textile structures for these applications are fairly simple in terms of material homogeneity and fi bre orientation.

For masonry applications, static or dynamic measurements may be desired. Plastic optical fi bre integrated textiles interrogated using OTDR are quasi-static (e.g. seconds for signal acquisition and minutes for a stable response) but are robust in that they can undergo up to 40% strain before failure. Such systems are effective at detecting cracks. Dynamic measure-ments instead require the use of glass optical fi bre and FBG sensors. High frequency measurements are necessary to capture a structure response to events such as earthquakes and many SHM methods are based on dynamic measurements. For civil structures, a minimum interrogation frequency of 20 Hz is desired. Most commercial interrogation units exceed this frequency by orders of magnitude, the only concern being cost. The development of new systems for civil applications where many units would be necessary

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(a)

(b)

(c)

11.11 (a) A sensor-embedded geotextile fi lter mat, (b) a sensor-embedded geogrid, and (c) light through a fi bre optic embedded multiaxial textile for masonry applications (courtesy of Extreme Materials, Italy, the Saxony Textile Research Institute, Germany, Alpe Aldria Textile, Italy, Smartec, Switzerland, and Selcom Multiaxial Technology, Italy).

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(for permanent installation) is working towards solutions with the appropri-ate number of channels and frequency at an attractive cost. The textile structures for masonry applications are more complex in terms of material composition (e.g. glass, carbon, and Kevlar) as well as fi bre orientations (e.g. multiaxial fabrics).

11.5.3 Characterization and standardization

The material performance characterization and standardization of smart textiles pose several unique challenges. In cases where textiles are already in use with established guidelines, it is only a matter of demonstrating that the new sensor embedded textiles satisfy existing requirements. This sce-nario is generally the case for geotechnical applications. For masonry appli-cations where a new material system is being established, such guidelines must be created. For masonry construction, system performance is a func-tion of the textile structure employed (fi bre material type(s) and fi bre directions), the mortar selected to integrate the structure and the textile, the dimensions and material composition of the walls of the host structure, and the vertical preload (from upper storeys) present in the wall. The appli-cation to masonry structures also requires careful planning for cabling and integration. Despite these challenges, the multifunctional nature of these textiles (reinforcement and monitoring) makes them very attractive for the repair, retrofi t, and seismic upgrade of unreinforced masonry structures located in earthquake-prone areas.


Information from equipment manufacturers can be obtained from their websites. Most of them include basic information on the technology, and some selected papers on applications. Wikipedia also includes some brief and good summaries.

References cited in this chapter have been selected as the most signifi -cant on this topic. The group of Los Alamos, built around Dr Chuck Farrar, is recognized as one of the main contributors to SHM. They have a website with updated and very relevant information. Victor Giurgiutiu was also a pioneer in the fi eld of SHM, and his book is a particularly clear and well written source from which to learn about conducting SHM with piezoelectrics.

Professor Measures at UTIAS (University of Toronto, Institute for Aerospace Studies) started developing fi bre optic sensors very early, and integrating them into structures. Canada is still a leading country in this technology, particularly when applied to bridge monitoring. His book is also highly recommended. Finally, the handbook compiled by Prof.

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Lopez-Higuera on fi bre optic sensors has merged the inputs from most of the people active in the fi eld.

11.7 References

Casciati S., Faravelli L. (2009), Vulnerability assessment for medieval civic towers. Structure and Infrastructure Engineering, vol. 5, no. 1, doi: http://dx.doi.org/10.1080/15732470802664290

Frangopol D.M., Messervey T.B. (2009), Life-cycle cost and performance prediction: Role of structural health monitoring. Chapter 16 in Frontier Technologies for Infrastructure Engineering, S.-S. Chen and A.H.-S. Ang, eds, Structures and Infrastructures Book Series, Vol. 4, Boca Raton, London, New York, Leiden: CRC Press/Balkema, pp. 361–381

Giurgiutiu V. (2008), Structural Health Monitoring with Piezoelectric Wafer Active Sensors. Amsterdam, Boston: Academic Press

Glisic B., Inaudi D. (2007), Fibre Optic Methods for Structural Health Monitoring. Chichester, UK: John Wiley & Sons

Liehr S., Lenke P., Wendt M., Krebber K., Seeger M., Thiele E., Metschies H., Gebreselassie B., Münich J.C. (2009), Polymer optical fi ber sensors for distributed strain measurement and application in structural health monitoring, IEEE Sensors Journal, vol. 9, no. 11, pp. 1330–1338

Lopez-Higuera J.M. (2002), Handbook of Optical Fibre Sensing Technology. Chichester, UK: John Wiley & Sons

Measures R.M. (1989), Smart Structures with Nerves of Glass. Progress in Aerospace Sciences (ISSN 0376-0421), vol. 26, no. 4, pp. 289–351

Saleh B., Teich M. (2007), Fundamentals of Photonics. New York: Wiley InterScienceSohn H., Farrar C., Hemez F., Shunk D., Stinemates D.W., Nadler B.R. (2003), A

Review of Structural Health Monitoring Literature: 1996–2001. Los Alamos National Laboratory Report, LA-13976-MS

Teitelbaum M.E., Yarlagadda S., O’Brien D., Wetzel E., Goossen K.W. (2008), Normal incidence free space optical data porting to embedded communication links. IEEE Transactions on Components and Packaging Technologies, vol. 31, no. 1, pp. 32–38��


351

12Textiles for insulation systems, control of solar

gains and thermal losses and solar systems

J. M. CREMERS, Hochschule für Technik (HFT) Stuttgart, Germany and Hightex GmbH, Rimsting,

Germany

Abstract: This chapter discusses specifi c energy-related aspects of membrane structures such as highly effi cient translucent thermal insulation, options to control solar gains and options to reduce thermal losses by the application of newly developed functional coatings on fabrics and foils. Furthermore, it introduces new ways of integrating and applying highly fl exible amorphous thin-fi lm photovoltaics on PTFE/glass fabrics and ETFE foils. All topics discussed are exemplifi ed by executed buildings most of which are worldwide fi rsts of their kind with regard to the aspect described.

Key words: translucent aerogel insulation, functional selective low-emissivity coatings on PTFE/glass fabrics and ETFE foil, highly fl exible amorphous thin-fi lm photovoltaics on PTFE/glass fabrics and ETFE foils (PV fl exibles), projects: Georgia Tech’s Pavilion for Solar Decathlon 2007 (USA), Suvarnabhumi New Bangkok International Airport (Thailand), Dolce Vita Tejo shopping mall, Lisbon (Portugal), PV-ETFE-Pneu, Rimsting (Germany), PV-PTFE/Glass canopy, Rimsting (Germany).

12.1 Introduction

Besides glass, a variety of other translucent materials are highly attractive to architects: plastics, perforated metal plates and meshing, but maybe most of all membrane materials which can also withstand structural loads. Earlier applications of textile materials have served the purpose to keep off sun, wind, rain and snow while offering the advantage of enormous span widths and a great variety of shapes. The development of high-performance mem-brane and foil materials on the basis of fl uoropolymers, e.g. translucent membrane materials like PTFE-(polytetrafl uoroethylene) coated glass fi bres (PTFE/glass) or transparent foils made of a copolymer of ethylene and tetrafl uoroethylene (ETFE) were milestones in the search for appro-priate materials for the building envelope. The great variety of the projects completed by Hightex and others in type and scale shows the enormous potential of these high-tech building materials which in their primordial form of appearance are among the oldest of mankind – their predecessors,

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animal skins, were used to construct the fi rst kind of building envelopes, namely tents.

All technologies described in this chapter can be applied on prestressed membrane structures (e.g. single-layer roofs or facades) but also on pneumatic cushions made from tight materials like coated fabrics or foils. Compared to free-spanning single-layer applications, these infl at-able structures are relatively new as an established subject of architecture (and not only as a piece of ‘engineering structure’) – they have entered the architectural world only since the early 1960s (Otto, 1967; Herzog, 1977).

The energy-related aspects and physics of building envelopes that offer more than weather protection properties are rather complex. Figure 12.1 depicts the most relevant properties and isses exemplifi ed for a three-layer pneumatic cushion structure.

12.2 Heat protection for membranes: fl exible

translucent thermal insulation

Textiles used in construction are typically employed as weather protection due to their ability to span large distances and to take on any number of shapes. As a result of increased research and development of suitable active and passive solar technologies, the range of tensile-structure applications will increasingly extend beyond weather protection. These developments deal with passive measures such as improving control of solar gain and thermal insulation, as well as optimising acoustic and daylight characteris-tics. At approximately one fortieth of the weight of comparable structures employing glass, infl ated and mechanically tensioned membrane structures are unarguably lightweight. The amount of material required and the sil-houette of the supporting structure are minimised. But due to the optimised thicknesses – some under 0.2 mm thick – and despite the low thermal con-ductivity of synthetic materials, membrane structures lack favourable thermal insulation properties. Rectifying this defi cit necessitates either working with multi-layer assemblies and air spaces or, if higher values are specifi ed, utilising opaque insulation materials, such as mineral wool or a transparent or translucent thermal insulation. The latter are typically unde-sirable for a foil structure as they sacrifi ce one of the most important fea-tures, light transmission. As one of the other key features is the low weight of the membrane materials, which requires adequate light insulation, the author has been examining the options of using highly effi cent vacuum-insulation systems like vacuum insulation panels (VIP) in membrane structures (cf. Cremers, 2006). These insulation systems are still opaque but there are future options to produce translucent or even transparent variants.

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12.2.1 Silica aerogels in membrane structures – properties and principles of utilisation

One of the most promising options of fl exible insulation materials to be used for translucent foil structures involves granular silica aerogel as insula-tion material – see Fig. 12.2 (Cremers, 2008). Not only does aerogel have excellent thermal-insulation properties (see r-values and U-values in Fig. 12.3), but it is translucent as well.

12.2 Granular Silica Aerogel (Nanogel®) by Cabot Corp.

0

Aerogel

Mineral wool

Loose-fillcellulose

Fibreglassblanket

Rockwool

Perlite

2 4 6 8 10

R-value

U-value

0 0.5 1 21.5 2.5

12.3 Insulation values of existing building insulation products (values are per 1 inch or 25 mm of material). R-value: North America (hr·ft2F/Btu); U-value: Europe (W/m2K).

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Textiles for insulation systems 355


Silica aerogels are organic silicon bonds with a granule size of 0.5–4.0 mm, with pore diameters of 10–100 nm and a pore volume fraction of more than 80%. The light transmission of an aerogel layer is approximately 80% per cm installed, whereby the insulating properties, in relation to the thickness of the layer, are twice as good as those of polystyrene foam. In addition, this material is incombustible, sustainable, recyclable, heat resistant to 600°C, UV resistant and hydrophobic, and exhibits long-term stability, making it particularly well suited to use in construction. The original manu-facturing process was elaborate because it involved ‘supercritical drying’. In the last decade the process has been simplifi ed, enabling a wider distribu-tion of this group of materials. Silica-aerogels are available as fi ne particles, granulate and monolithic blocks. Aerogel’s light-scattering properties provide not only for a uniform underside, but also for comfortable, glare-free indoor light conditions.

12.2.2 Aerogel fi lling in pneumatic structures

For utilisation in pneumatic ETFE cushions – where exploiting natural light plays an important role – translucent aerogel is a suitable selection. A thick-ness of only 3 cm has a thermal transmission coeffi cient (U-value) of 0.57 W/m2K, and the light transmission factor is 45% (compare Fig. 12.3). The aerogel stratum can be installed in the top or bottom layer of the ETFE cushion. To this end, the respective layer is ‘doubled-up’: instead of a single layer, two layers of ETFE foil are specifi ed, between which the aerogel is introduced. The precise amount of aerogel required is determined by con-sulting the cut plan for the ETFE layers. The material introduced in the ETFE cushion is evenly distributed; a constant layer thickness results. This will be stabilised by the pressure in the cushion. If the cushion has a third (middle) layer, it would also be possible to introduce insulation here. ETFE foil is relatively open to moisture diffusion and, as a result, allows small amounts of water vapour to penetrate the insulating level. But thanks to aerogel’s hydrophobic properties, the water is not absorbed by the granules and can subsequently escape from the panel.

12.2.3 Aerogel fl eece/wrap

Due to the absence of a stabilising pressurisation in mechanically tensioned structures, another type of aerogel insulation is employed. This version is a fl eece made of two-component fi bres which is sprinkled with aerogel particles. This produces a fl exible and pressure-resistant mat which has highly favourable insulating properties. This fl eece can be used both in combination with transparent ETFE foils and with translucent membrane materials such as PTFE-coated, glass-fi bre fabric – see Fig. 12.4. The

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translucent fl eece is ideally installed directly on the lower membrane layer and only negligibly reduces light transmission. In contrast to granules with which a uniform appearance is achieved, here the seams of the individual batts can detract from the appearance. Particularly for foil structures of transparent ETFE, this effect may be undesirable. For this type of application, where appropriate, two or more layers of fl eece with staggered seams are recommended. This is advisable to avoid compromis-ing the strength of the insulation layer through linear thermal bridges at the butt seams.

12.2.4 Employing aerogel cushions – a case study

Georgia Institute of Technology’s entry to the competition Solar Decathlon 2007, developed and realised by SolarNext AG in cooperation with Hightex GmbH, implemented a concept for a highly insulated, semi-transparent roof and showcased aerogel. In 2007, the US Department of Energy spon-sored a competition for energy-optimised construction. The designs were to be developed by interdisciplinary teams at universities. The goal was to design and realise an optimised, energy-effi cient, solar-powered and archi-tecturally appealing residential unit. Among the evaluation criteria were architecture, structure, technology, lighting and the energy balance. Emphasis was placed on intelligent and innovative utilisation of new mate-rials as well as on sensible usage of established building materials. The individual roof elements, developed by SolarNext/Hightex expressly for the competition, were prefabricated to as great a degree as possible in the factory, because the aim was that the students assemble it on their own.

12.4 Fleece/wrap: fi brous formation aerogel.

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The structure was divided into two levels, separated by function. The lower level consists of highly insulated panels which also serve as the underside of the ceiling, while the upper level functions solely as weather protection. The lower level is comprised of nine ceiling panels measuring 4 × 1.5 m. These ceiling panels are made of a thermally separated framework with optimised cross-section which is tensioned with an ETFE foil and then fi lled with aerogel. A principal section drawing is shown in Fig. 12.5. The result is an illuminated ceiling with a uniform appearance over the panel’s entire visible surface, with a light transmission factor of about 20% and a U-value of approximately 0.3 W/m2K. The upper level of the roof is an ETFE-tensioned arch: because it is independent of the insulating level and spans only 1.5 m, it enables a correspondingly simple realisation and mini-mised cross-sections. A view from top outside is provided in Fig. 12.6. Figure 12.7 illustrates the interior view to the light ceiling. It is generally advisable to provide shading devices for translucent wall or roof elements which are insulated with aerogel because otherwise there will be increased energy input. The translucent ceiling for the Georgia Institute of Technology’s pavilion did this by shielding a large portion of the radiation with photovoltaic elements mounted on the roof. In addition, adjustable

12.5 Solar Decathlon 2007 – roof section through the aerogel/ETFE cushion.

12.6 Solar Decathlon 2007 – exterior view of the aerogel/ETFE roof.

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sun protection was installed. The result is a lightweight, highly insulated roof which, due to its translucence, optimally exploits the available daylight.

12.3 Selective and low-E functional coatings for

membrane materials (PTFE/ETFE)

12.3.1 Physical principle of transparent selective coatings

Heat transport can be differentiated into thermal convection, thermal con-duction (through gases and solid materials) and thermal radiation. All three ways have to be addressed when optimising a building envelope with regard to thermal protection against cold (winter) or heat (summer). The thermal protection properties of the building envelope are most important for the overall energy balance of a building. Therefore all parts of the building envelope have to be carefully designed to meet these criteria. Additionally, the energy fl ow through the building envelope is affected by different factors such as the temperature and radiation differences between inside and outside. Here, the dynamic exterior solar radiation is as important as the thermal radiation of all material surfaces inside the building (cf. Fig. 12.1). All kinds of measures for thermal protection, e.g. thermal insulation, have to address these complex scenarios.

The technology described in this part of the chapter addresses the radia-tive heat exchange between the building envelope to the outside and to the inside. Every material with a temperature above absolute zero (0 kelvin) emits energy by radiation towards a surface with a lower temperature. The

12.7 Solar Decathlon 2007 – interior view of the aerogel/ETFE roof.

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sun, which is an extremely hot mass, radiates with a spectrum specifi c to its high temperature which is the so-called ‘solar spectrum’. This can be divided into the ultraviolet (UV, wavelength 0.3 to 0.38 µm), visible (0.38 to 0.78 µm) and near infrared (near IR, 0.78 µm to 2.5 µm) parts. The human eye can only see radiation in the visible part, which is commonly called ‘light’. All these three parts transport energy by radiation (ratio approxi-mately: UV 5%, visible 45%, near IR 50%). When the solar radiation hits another material it may be partly transmitted, absorbed and/or refl ected depending on the material’s surface. When the solar radiation is absorbed the material’s temperature increases and therefore also the energy emitted by the material itself by radiation increases. For materials with moderate temperatures as in building envelopes this radiation happens in the far infrared (far IR) range of the spectrum at wavelengths of approximately 3 to 50 µm, which is also called ‘heat radiation’.

There are three different cases to investigate when using fabric materials: opaque, translucent and transparent building envelopes. Opaque envelopes prevent solar radiation in the visible part of the solar spectrum from enter-ing the building. This normally affects also the near IR part of the solar spectrum. Depending on the refl ectivity of the outer surface, part of the energy is refl ected. With PTFE/glass this is a relatively high percentage of approximately 70% and this value stays up when the surface is washed by rain regularly due to the lasting ‘self-cleaning’ effect of the PTFE surface. The other part of the energy, which is not transmitted, is absorbed and therefore leads to an increase in the material’s temperature. Translucent and transparent materials are directly transmitting a certain ratio of the solar radiation. Translucent materials have a diffusive light transmission whereas transparent materials interfere only minimally with the visible radiation (‘direct light transmission’). Again the other part of the energy is refl ected and absorbed in a ratio depending on specifi c material properties.

The transmission of solar radiation of a material is commonly differenti-ated into transmission for the visible part of the spectrum (ratio tvis) and transmission for the complete solar spectrum including the visible, the UV and the near IR parts (ratio tsol). Most light-transmitting materials have values with tvis ≈ tsol. However, in some cases it is highly benefi cial to have a building envelope with tvis > tsol to reduce the solar gains but to keep up the interior light level (less heat, more light). The ratio tvis/tsol is called the ‘selectivity’. On glass, this technology is available for decades now (‘sun protection glass’) which is achieved by so-called transparent selective coatings on the glass surface. Having been not neutral but coloured in the beginning, these coatings are now very neutral in colour. That means that the cutting line of the fi lter on the solar spectrum is very straight and steep.

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12.3.2 Physical principle of low-E surfaces

In the last paragraph it was explained that every material with a tem-perature above absolute zero (0 kelvin) emits energy (QS) by radiation towards a surface with a lower temperature. QS is given by the following equation:

Qs = σ ε1 ε2 (T14 − T2

4) 12.1

where

σ = Stefan–Boltzmann constant, σ = 5.67 × 10−8

ε1,2 = emittance of surfaces 1 and 2 (%)T1,2 = temperature of surfaces 1 and 2 (K).

Obviously, the surface temperatures are very infl uential for the radiative energy fl ow. But also the emittance of the surfaces is important. As the emittance is a surface quality property, it can be modifi ed by special surface treatments like coatings which are commonly known as low-E surfaces (low-E = ‘low emissivity’). By reducing the emittance of a building envelope material from >90% (standard fabric material) to e.g. <30%, the radiative heat transfer from the envelope is decreased by two-thirds (not regarding potential direct transmission). This effect can be used positively in winter to limit thermal losses if the layers facing outside are treated. But it can also be benefi cial in hot climates: if the low-E surfaces are applied facing inside they reduce the radiative heat transfer from the outside via the hot envelope material. Low-E surfaces can be applied to transparent, translu-cent and opaque materials. According to the physical laws a low emittance surface means always a high refl ectance in the same part of the spectrum (far IR in this case). This can be used additionally to increase comfort levels in the building when applied adequately.

As for selective layers, low-E surfaces have also been commonly known for decades now and are standard, for example, in the glazing industry. However, both technologies are very new in the world of membranes. Transparent selective coatings and low-E surfaces on glass are commonly applied to layers which are enclosed inside insulation glazing units. These units are fi lled with dry air or even argon or krypton and therefore their interior presents an ideal protective environment to prevent the functional layers from corrosion.

With membranes it is not possible to build a similar structure with a gastight space between two layers which would protect the functional layers equivalently. Therefore, a solution had to be found with non-corrosive functional layers that are able to withstand the interior environmental conditions of the building (or may even be exposed to the external weather conditions).

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12.3.3 Low-E coating on PTFE/glass fabrics

The fi rst application of low-E coated membrane material on a large scale has been the Suvarnabhumi International Airport Bangkok by architect Murphy/Jahn, Chicago. The new material development and the membrane structure were executed by Hightex based on an energy concept of Transsolar GmbH, Munich (Heeg, 2006; Holst, 2006). According to this concept the amount of energy used for the air conditioning of the huge interior space of the airport’s concourses (span width 42 m, total length 3 km) has been reduced by limiting the air conditioned zone to the fl oor area with a height of approximately 2.5 m which is the only part of the space used by people. This has been achieved by fl oor cooling and displace-ment ventilation close to the frequented circulation areas on the fl oor. Additionally, no U-value requirements for the building envelope have been set. The result is a constant temperature stratifi cation in the concourses, which is depicted in Fig. 12.8 as a result of a dynamic CFD simulation. The image shows that there are very high temperatures under the top of the roof which would lead to severe heat radiation from the roof back to the interior (like a huge radiator). To reduce this effect, a low-E surface has been successfully developed for the interior PTFE/glass layer. As thereby this coated inner liner also mirrors the cold fl oor temperatures back to the people, the interior comfort is improved even further.

The complex three-layer membrane of Bangkok Airport’s membrane roof is illustrated in Fig. 12.9. Here and as explained before, the high and lasting solar refl ection of 70% of the outer waterproof PTFE/glass layer is also an important feature. To improve the acoustic properties of the roof, an additional middle layer has been included which consists of a cable net covered with transparent polycarbonate (PC) sheets. This, in conjunction with the translucent inner membrane liner, acts as a baffl e. Figure 12.10 provides an interior view of the concourses with the innovative membrane envelope.

12.8 Temperature stratifi cation due to a limitation of air conditioning to the fl oor area and no U-value requirements for the building envelope.

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Solar radiation ontriple-layer membrane roof100%

Solar radiation onfritted glass100%

Reflection of solarradiation60%

Absorption36.5%

Absorption28%

Reflection of thesolar radiation70%

Transmission2%

Low-e-coating

Reduced long-wave radiationTransmission3.5%

Conditioned space

TLuft = 24°C

Toperative = 27°C

Supply air18°C, 4 ac/h

Intake13°C Floor cooling

Return19°C

Floor surface 21°C

12.9 Energy concept of Bangkok Airport’s concourses by Transsolar.

12.10 Interior of Bangkok Airport’s concourses showing the membrane building envelope.

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12.3.4 Low-E coating on ETFE foils

Obviously, the next step was to investigate and transfer the low-E technol-ogy to transparent ETFE foil with the aim of achieving a transparent selec-tive low-E material. The development of this ETFE material was started by SolarNext/Hightex in 2006. Results can be seen in Figs 12.11 and 12.12.

The new type of product has been applied for the Dolce Vita Tejo shop-ping mall near Lisbon, Portugal. The mall, which was opened to the public in May 2009, features the fi rst transparent selective low-E coatings on ETFE foil worldwide (Fig. 12.13). The coatings improve the thermal per-formance of the innovative geometrical cushion solution which shapes a north-light situation: the south-facing half of the top cushion layer is made with an opaque ETFE foil whereas the north-facing part is transparent. On

12.11 Transparent selective low-E coating on ETFE foil.

12.12 Opaque low-E coating on white ETFE foil.

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the lower layer this is turned around. Thereby, all direct solar radiation is prevented from entering through the roof.

12.4 Fully membrane-integrated photovoltaics:

PV fl exibles (PTFE/ETFE)

12.4.1 Application of photovoltaics in foil and membrane structures

For many reasons the integration of photovoltaics in buildings (building integrated photovoltaic – BIPV) offers much future potential. Benefi ts most commonly reported are, amongst others:

• The photovoltaic does not require an additional sub-structure as it is an integrated part of the building envelope.

• From an aesthetic point of view, an integrated solution offers far more potential than any add-on application.

• The photovoltaic not only provides electricity – in an appropriate appli-cation in transparent or translucent parts it might also provide necessary shading which reduces the solar heat gains in the building and thereby helps to minimise cooling-loads and energy demand in summer. This synergy effect is of most importance because it principally helps to reduce the so-called balance of system (BOS) cost for the photovoltaic application.

In a report the International Energy Agency (IEA) gives an estimation of the building-integrated photovoltaic potential of 23 billion square metres.

12.13 Dolce Vita Tejo shopping mall, desgined by Promontorio Architects.

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This would be equivalent to approximately 1000 GWp at a low average effi ciency of 5%. Suitable existing roofs and facades with good sunshine exposure in 14 selected IEA countries were examined in this study (IEA Report, 2004).

Up to now solutions for the integration of photovoltaics in free-spanning foil and membrane structures have not been available, although these struc-tures are predestined for the use of large-scale photovoltaic applications (shopping malls, stadium roofs, airports, etc.). There have been studies and experiments with the use of photovoltaics in transparent PVC membranes (see Fig. 12.14) but this group of materials did not prove to be suitable as it is not stable on a long-term base. And as clients require a return on investment within an appropriate time, the basis material in which the photovoltaic is embedded has to provide a suffi cient lifetime. Therefore, we believe that it is important to embed photovoltaics not into PVC but into long-lasting polymers, for example fl uoropolymers like ETFE or PTFE.

12.4.2 Scope of ETFE-photovoltaic and PTFE-photovoltaic application

While PTFE-coated membrane material has already been used in the build-ing industry for a longer period of time, a signifi cant annual increase in the installed area of pneumatic structures using ETFE can be seen during recent years. Most of the structures are roof applications, though some are

12.14 First photovoltaic tensile structure at the ‘Under the Sun’ exhibition at the Cooper-Hewitt National Design Museum, New York, 1998, designed by FTL Design Engineering Studio.

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facades. Up to now it has been impossible to equip these two constructions with integrated photovoltaics. The developments described here (fi rst pub-lished in Cremers, 2007; see also Cremers, 2009) will allow market segments of the building industry to be addressed which are not accessible to rigid and heavy solar modules in principle.

12.4.3 Photovoltaic technology and principles of application

The photovoltaic technology used has been developed at the University of Neuenburg (Université de Neuchâtel) in Switzerland (Shah et al., 2004) and is now produced and supplied by a spin-off company, VHF-Technologies SA, Avenue des Sports 18, CH-1400 Yverdon-les-Bains, Switzerland (Bailat et al., 2005). Basically it is a special process of manufacturing amorphous silicon thin-fi lm photovoltaic cells on thin polymer fi lm. The photovoltaic cells are coated in a multi-layer process on the polymer substrate in a con-tinuous production technique (roll-to-roll process). Being a variant of amorphous silicon thin-fi lm technology, the process requires signifi cantly less silicon and energy compared to the production of solar cells from mono- or polycrystalline silicon. The technology even has the potential of reaching lower system costs than thin-fi lm Si on glass. Also the energy payback time is relatively short (about 1.2 years for conventional modules compared to 2 years for mono-Si-modules). Here, the energy payback time is given for a roof-top system located in Southern Europe for conventional thin-fi lm modules (not ETFE laminates) as a result of the SENSE project (Alsema et al., 2006). The cost reduction potential of this technology, according to a study by Q-Cells, is the highest amongst all others: for 2010 total system costs can be up to 70% lower than the current cost of most Si systems (multi-Si, mono-Si, string ribbon Si, values for 2006) (Hartley et al., 2006). The resulting photovoltaic fi lm material is very thin (approximately 51 µm) and very light in weight. Therefore, it is predestined for use in mobile applications. But as it is fully fl exible at the same time (see Fig. 12.15), it is also an appropriate option for application on membrane constructions.

The photovoltaic rolls produced can be cut to lengths according to the specifi c project’s need (Fig. 12.16(a)). The strips are then arranged and assembled in laminates (see Figs. 12.16(b) and 12.17): the photovoltaic fi lm layer is embedded in two ETFE fi lms of equal or different thickness. The lamination protects the photovoltaic fi lm from mechanical impact and stress, humidity, weathering, etc. ETFE has been commonly used in the building industry for translucent and even transparent envelope construc-tions for decades now and has proved to be of long-term value as it is very stable against weathering infl uence, including UV irradiation. It is not

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12.15 Fully fl exible a-Si PV on polymer substrate.

(a)

(b)

(c) (d)

12.16 (a)–(d) Manufacturing steps of ETFE-embedded PV modules.

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measurably degrading and keeps its unique surface qualities (anti-adhesion, clear and high transparency) over time (Koch, 2004).

The size of the laminates is actually limited by the size of the lamination machinery (approximately 3.5 m × 2 m). Therefore, for many projects the single laminates have to be combined into larger sheets which are used to build roofs or facades with single-layer structures or multi-layer cushions (pneumatic structures). The laminates are then cut with regard to the fi nal 3D-shape followed by the joining of the edges in a special welding process (Figs 12.16(c) and (d)).

The photovoltaic can be integrated in pneumatic constructions such as foil cushions (as can be seen in Fig. 12.18). The application in the middle layer will protect the photovoltaic but limit the power output due to refrac-tion effects (of the top layer foil) and also due to the heating of the absorp-tive middle layer which will not be reduced by convection effects of the outside air. Therefore, the integration on the outer top layer of the cushion will be more effi cient.

For application in combination with translucent PTFE-coated membrane material, fl uoropolymers are used that can be tied positively to the PTFE coating of the membrane. Figure 12.19 shows how the modules are attached to the coated translucent fabric material. Of course, the modules reduce the light transmission to virtually zero where applied, but from under-neath (an important viewing direction) the effect is decreased by the contrast reducing the light diffusion of the translucent white fabric mate-rial, as can be seen in Fig. 12.20. With this technology a small four-point sail has been built in Rimsting outside Hightex’s offi ce building in Germany (Fig. 12.21).

12.17 PV fl exibles: ETFE embedded a-Si PV.

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12.18 Principle of PV fl exibles integrated in the top layer of an ETFE cushion, providing shading and electrical power.

12.19 PV fl exibles applied to PTFE/glass fabric membrane.

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12.20 PV fl exibles applied to PTFE/glass fabric membrane - transmission view against the light.

12.21 Small four-point sail with a PTFE/glass membrane featuring applied PV fl exibles.

The computer rendering in Fig. 12.22 illustrates how a stadium roof fea-turing PV fl exibles could look: the Mercedes Benz Arena in Stuttgart, Germany (status quo in Fig. 12.23).

Figures 12.24 and 12.25 show the Hightex Offi ce in Rimsting, Germany: PV fl exibles – application to pneumatic roof construction (ETFE), 2007:

• Two-layer ETFE cushion, 5 m × 5 m• Area of top layer: 25.7 m2

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12.22 Mercedes Benz Arena, Stuttgart, Germany, with PV fl exibles (computer rendering).

12.23 Mercedes Benz Arena, Stuttgart, Germany, with PV fl exibles.

• Coverage of PV-area (active PV module area): 9.3 m2 (37.4%)• Installed power approximately 440 Wp.

Figure 12.24 shows details of the exterior view, and Fig. 12.25 the view from inside.

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12.4.4 Photovoltaic output forecast

The output forecast for photovoltaic integrated in foil and membrane con-structions is signifi cantly more complex than for standard photovoltaic arrays, for the following reasons:

• Shapes will vary for each project, resulting in different layouts for the integrated photovoltaic. There is hardly anything like a standard sce-nario (which would allow for a standard ‘product’-like development).

• Exposure of the photovoltaic to the sun will vary greatly within each project as the photovoltaic follows the foil or membrane form-fi nding

12.24 PV Flexibles integrated in an ETFE cushion of 5 × 5 m, Rimsting, Germany.

12.25 PV Flexibles integrated in an ETFE cushion of 5 × 5 m, interior view.

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process which is driven by the substructure and the structural loads. And in principle the surfaces will always be curved in two directions (anticlastic) because otherwise they would not be stable.

• The complex three-dimensional shapes will also complicate the calcula-tion of potential shading effects.

12.5 Conclusion

The variety of new technologies developed in the fi eld of foil and mem-brane construction and materials is defi nitely expanding and enriching architectural design options to realise advanced technical solutions and new shapes. Selected options to improve the performance of membrane building envelopes are listed in Fig. 12.26.

However, a solid background of know-how and experience is needed to derive full advantage from the innovative and intriguing possibilities on offer. As an architect or designer you can only feel comfortable with tech-nologies of which you have at least a basic understanding. This actually poses a great challenge to the educational system for architecture but also

Prestressed

Improvement of thermal insulation byadditional insulation material or integrationof an insulation system

Improving thermal energy storage properties, e.g.by implementing phase change materials (PCM)

Integration of light emitting layers on thematerial surface

Integration of switchable/auto-switchingfunctional layers to controll the g-Value/SHG

Application of an additional functional layeror coating on the material surface withselective and/or low-e-properties

Application of additional layers or coatings onthe material surface to minimise dirt adhesion

Design of switchable layers(controlling light and energy transmission)

Design of movable structures(controlling light, ventilation, shading)

Integration of layers improving the acousticproperties of the structure (improvingsound absorption or reduction of soundtransmission)

Integration of photovoltaics

Building envelope... structural system...

Future issues:

Advanced membrane building envelopes Selected options to improveperformance

Pneumatic

Pneumatic

... With climaticrequirements

... Without climaticrequirements

Prestressed

12.26 Options for improving the performance of membrane building envelopes.

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to the membrane industry, which is a relatively small sector. At the end, every new product and technology has to be introduced to the market and made known to architects and designers, which needs resources for marketing activities and promotion. Also, it requires a great deal of pre-acquisitional activities of direct consulting to planners in early design stages to enable the development of functional and technically sound but also economic solutions. Therefore, it will be a long (but still very promising) road to follow until the technologies described here will be commonly used in the building sector and become something that could be called a ‘standard’.

12.6 References

Alsema E et al. (2006), Environmental impacts of PV electricity generation – a critical comparison of energy supply options, In 3rd PV Industry Forum, Dresden, Germany, pp. 3201 et seq.

Bailat J et al. (2005), Recent development of solar cells on low-cost plastic sub-strates, In Proceedings of the 20th EU Photovoltaic Solar Energy Conference, Barcelona, Spain, pp. 1529–1532

Cremers J (2006), Einsatzmöglichkeiten von Vakuum-Dämmsystemen im Bereich der Gebäudehülle – technologische, bauphysikalische und architektonische Aspekte, Munich and New York, Martin Meidenbauer

Cremers J (2007), Flexible photovoltaics integrated in transparent membrane and pneumatic foil constructions, In Proceedings of the CISBAT 2007 Conference, EPFL, Lausanne, Switzerland

Cremers J (2008), Translucent high performance silica-aerogel insultation for mem-brane structures, Detail, English Edition, issue 4-2008, pp. 410–412

Cremers J (2009), Integration of photovoltaics in membrane structures, Detail Green, issue 1-2009, pp. 61–63

Hartley O, Malmström J, Milner A (2006), Driving the PV industry towards com-petitiveness (Q-Cells presentation), 3rd PV Industry Forum, Dresden, Germany, pp. 3217–3220

Heeg M (2006), Suvarnabhumi International Airport Bangkok – engineering, manu-facturing and installing the membrane roof, Detail, issue 7/8 – 2006, pp. 824 - 825

Herzog Th (1977), Pneumatic Structures – A Handbook for the Architect and Engineer, London, Crosby Lockwood Staples

Holst S (2006), Suvarnabhumi International Airport Bangkok – innovative climate concept, Detail, issue 7/8 – 2006, pp. 820–823

IEA Report (2004), PVPS T7-4, International Energy AgencyKoch K-M (ed.) (2004), Membrane Structures, Munich, Berlin, London and New

York, PrestelOtto F (1967), Tensile Structures, Cambridge, MA, MIT PressShah A et al. (2004), Thin-fi lm silicon solar cell technology, Progress in Photovoltaics:

Research and Applications, vol. 12, pp. 113–142SolarNext AG/Hightex Group (2007), Datasheet for product ‘PV Flexibles’, www.

hightexworld.com (2007/2008)

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375

13Sustainable buildings: biomimicry and

textile applications

E. HERTZSCH, University of Melbourne, Australia

Abstract: With sustainability becoming an integral part of our lives, this chapter looks at the application of textile materials in buildings with regard to reducing their operational energy. Results of a survey (Chapter 14) on the uptake of textile materials in Australia indicate challenges for their implementation and the need for further clarifi cation on material characteristics and application possibilities. This chapter provides strategies on how to increase the energy effi ciency as well as examples for new forms of applications. The integration of textiles in buildings will be compared with examples from nature to inspire and provoke ideas for further development in this fi eld.

Key words: fabric facade, textile materials, biomimicry, energy effi ciency, sustainability.

13.1 Introduction

The biggest area of improvements with regard to the mitigation of climate change is buildings, as shown in Fig. 13.1 (IPCC, 2007). The built environ-ment is responsible for approximately one-third of energy-related CO2 and three-fi fths of halocarbon emissions. Figures around 25–40% are men-tioned when it comes to the contribution of buildings to the energy con-sumption in many countries (OECD, 2003).

The world of today not only consumes vast amounts of energy but also needs natural resources for creating and maintaining the built environment. The reduction of resources used for the manufacturing, transportation, marketing and other resource-demanding needs for a building element is of utmost importance and one of the major challenges we face in order to survive on this planet.

With regard to energy effi ciency, one of the crucial elements to look at is the building envelope. Despite its architectural appearance, the facade has the ability to transmit light and heat as well as fresh air. This impacts directly on the building’s heating and cooling load due to ingress of solar radiation, air temperature and, indirectly, the need for electricity for arti-fi cial light depending on the light penetration through the facade. The envelope can also allow for natural air to fl ow through the building during

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13.1 Areas of improvement with regard to the mitigation of climate change; from Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Figure 4.2. IPCC, Geneva, Switzerland (IPCC, 2007).

Energysupply

Transport Buildings

total sectoral potential at <US$100/tCO2-eq in GtCO2 -eq/yr:

US$ 100/tCO2-eq

Non-OECD/EIT

EIT

OECD

World total

Industry Agriculture Forestry Waste

2.4–4.7

<20

<50

<100 <2

0<5

0

<100 <2

0<5

0

<100 <2

0<5

0

<100 <2

0<5

0

<100 <2

0<5

0

<100 <2

0<5

0

<100

GtCO2-eq/yr7

6

5

4

3

2

1

0

1.6–2.5 5.3–6.7 2.5–5.5 2.3–6.4 1.3–4.2 0.4–1.0

the day (e.g. cross-ventilation) or night (e.g. night purge) according to the openings and the building management system. In general, savings of 50–75% are possible when the building envelope and the building systems are improved. Focusing on the incorporation of a suitable envelope alone can result in operational energy savings of 35–50% (Harvey, 2009).

The transparent elements of a facade can be responsible for a high heat and light fl ux. Studies in both cold and warm climates have shown annual increases of 90 kWh/m2 and 200 kWh/m2 up to 150 kWh/m2 and 350 kWh/m2 when the window area was raised from 40% to 100% (Ghisi and Tinker, 2001). Textile materials can be highly transparent and their application should therefore be considered thoroughly with respect to their impact on operational energy consumption.

In this chapter, applications of textile materials to buildings are compared with examples from nature to inspire, provoke new ideas, and develop further fi elds of implementation. We live in a world of fascinating nature that can and already has inspired mankind with many technical solutions. When we look at the living world, we might fi nd models that can be mimicked to create and/or maintain a resource-friendly built environment (Pedersen, 2008). Creatures have evolved and refi ned their bodies to suit the specifi c climate zones they live in. Plants have increased the effi ciency of how they deal with their natural environment from one generation to the next in order to adapt.

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Sustainable buildings: biomimicry and textile applications 377


‘Plants are highly effi cient solar collectors harvesting solar energy. They use solar energy to transform carbon dioxide from the air into chemical energy while enriching the atmosphere with oxygen. As biomass, they are an energy source in their own right and form the starting point for the food chain that sustains most living creatures on earth’ (Behling and Behling, 1996). Principles, strategies, tools and methods animals and plants are using can possibly be transferred to the built environment, thereby aiming to increase our effi ciency of material use and energy consumption.

The examples of applications in this chapter focus on operational energy savings to present insights into the vast implementation possibilities of textile materials, such as glass-fi bre mesh, polytetrafl uoroethylene (PTFE) and ethylene-tetrafl uoro-ethylene (ETFE). This chapter provides:

1. An overview of challenges for the implementation of textile materials in Australia

2. Strategies for facades to reduce the operational energy demand of buildings thereby addressing the challenges mentioned above

3. Applicable knowledge on the contributions textile materials can provide to reduce operational energy, comparing these with examples from nature.

13.2 Implementation of textile materials in Australia

The University of Melbourne undertook a survey of Australian architects with regard to their perception of the future applications of textile materials in energy-effi cient buildings. The survey was accomplished by Kimberly Lau, supervised by Associate Professor Eckhart Hertzsch, as part of a subject called ‘Research Project’ in the Property and Construction Course at the Faculty of Architecture, Building and Planning, and focused on the comparison of PTFE and ETFE with glass.

The survey targeted substantial architectural fi rms that have interna-tional as well as national projects. The majority of the architects have 10–20 years of experience in the design and construction industry and a high level of experience in energy-effi cient building and facade design (Lau, 2009). The full details of the survey, its objectives and results are provided in Chapter 14. The following paragraphs will discuss possible solutions and information to overcome the obstacles mentioned in this survey. Although this interview was conducted in Australia, it is believed that the information is an exemplar of issues that are worth addressing in other countries as well.

13.2.1 Major obstacles

Several issues exist that seem to hinder textiles becoming a mainstream facade material, as glass is. These are as follows (Lau, 2009):

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1. Daylight and shading: Confl icting ideas exist. The daylight transmission of ETFE is perceived by 75% as ‘acceptable’ to ‘excellent’, but the shading capability is regarded as ‘poor’ by 25%. In contrast to that, 67% of the architects rated the shading capabilities of PTFE as ‘accept-able’ to ‘excellent’, which might stem from the most common applica-tion of PTFE as a shading of car-ports and the like.

2. Ventilation: None of the architects thought that the ability to provide natural ventilation with ETFE cushions was ‘excellent’; 33% did not see a possibility of how the material could incorporate this function. On the other hand PTFE was regarded as ‘acceptable’, with 58% think-ing that ventilation could be done.

3. Life-cycle costing: Architects did not know how the life-cycle costing of ETFE and PTFE would compare to glazing, 58% and 60% respec-tively, thereby showing very little knowledge on the maintenance and self-cleaning advantages of both ETFE and PTFE.

4. U-value: 42% rated ETFE better in its ability to slow down the heat transmission in comparison to glass, whilst the same number of archi-tects perceived the U-value of PTFE to be lower than that of glass.

5. Embodied energy: While 30% of the interviewees did not know this for ETFE and PTFE, 50%/42% thought that ETFE/PTFE has a lower embodied energy than glass, but 33% considered PTFE to be higher in its embodied energy compared with glass.

6. Recyclability: 33% thought that ETFE has a lower potential for reuse than glass; for PTFE 50% perceived it to be the same. In fact all products are recyclable.

7. Cost: One-third of the group thought that ETFE would be more expen-sive than glass as a whole facade system, while 25% thought it could be cheaper and 25% were unsure how to compare. PTFE was perceived as cheaper by 50%; 16% thought it to be more costly.

8. Other obstacles: Both ETFE and PTFE were perceived to have prob-lems with regard to their structural integrity and resistance to vandalism, distorted vision through the material and a ‘why change?’ attitude of the client, as well as reasons embedded in issues of Australian cultural conservatism.

Not an obstacle, but a very important factor is probably that 95% of the architects liked the aesthetics and architectural appearance of existing facade applications, thus being inclined to continue to use them. This is obviously a very important factor as this in itself can lead to many applications.

The above clearly shows areas where knowledge improvements are required:

• Daylighting and shading• Thermal performance

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• The integration of a possibility to naturally ventilate• Life-cycle costing and cost comparisons in general• Embodied energy• Recyclability.

The following sections will increase the reader’s knowledge in the above fi elds. Firstly, general information will be provided on criteria and strategies needed to achieve a facade that reduces the operational energy demand of a building. Secondly, examples will be shown for these general strategies, focusing on daylighing and shading, thermal performance and natural ventilation. To further inspire and create ideas for concepts and possible applications, examples from nature are presented for each of the topics mentioned above.

13.3 Strategies for facades to reduce the operational

energy demand

In general, a building is located in a particular environment and has certain types of uses. The outdoor macro- and micro-climate provide the building with light and air temperatures of certain magnitudes. The use of the prop-erty, with a specifi c number of occupants and their machinery (PCs, print-ers, artifi cial light, etc.) creates more or less heat in the building, and also requires visual, thermal and acoustic comfort parameters to be fulfi lled for the building’s occupants.

In most climate zones the outdoor conditions vary on an hourly basis during the day; even in climate zones where the average temperature does not change a lot, e.g. in Singapore, the amount of daylight varies signifi cantly.

Depending on the impact of the outdoor environment on the indoor ‘heat production’ due to its occupants and their tasks, the following principal situations would occur if no temperature-regulating system were active in the building:

• Heat ingress or egress where the temperature outside the building is either warmer or cooler than inside, thus creating a heat fl ux that is directed towards the outside or inside

• Direct solar radiation and/or diffuse daylight where, relative to the ‘cloudiness’ of the sky and the time of the day, the radiation varies constantly throughout the day.

Due to the facade design and performance:

• The internal luminance values created by the sky conditions are within, above or below the occupants’ comfort zone.

• The indoor air temperature needs to be cooled or heated according to the magnitude and distribution of the internal heat sources, such as people, machines, use of artifi cial light, etc.

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Depending on the latitude and longitude of the building’s position and its use, the above situations can occur in many different combinations. For example, the cooling load can occur when the outside temperature is higher than inside (heat entry) as well as vice versa; the same applies to the heating load. In addition, the sky conditions can create luminance values that occur independently of either heat entry/loss or cooling/heating load. This can mean that certain functions or components in the building envelope should work separately; e.g. glare protection could be provided independently from daylight distribution, or a shading system to prevent glare can be used either inside or outside the building according to the changing energy modes.

Although human beings sometimes feel a stimulating effect when sudden light changes occur, normal working conditions generally need light levels to be constant, or at least in a restricted range. For visual comfort the effect of glare needs to be minimized. Another important factor is the reduction of changing light levels to prevent constant adaptation to luminance intensi-ties of different magnitudes (Bartenbach, 2001).

The thermal requirements are equally a constraint. Most people, it seems, feel comfortable with an air temperature ranging between 20 and 24°C. Occupants also feel a ‘mean radiant temperature’ – an average of the surface temperatures of all surrounding elements. This makes the facade’s internal surface temperature a very important factor as it infl uences the occupants’ comfort according to their position relative to the building envelope.

These are only a few of the comfort requirements that need to be con-sidered when designing a building. In general, human beings seem to feel most ‘comfortable’ when the visual and thermal conditions are within a small range (Nicol and Humphreys, 2002; Bartenbach, 2001).

To save energy means fulfi lling these indoor environmental requirements with the utmost minimum use of fossil fuel-consuming energy – or, to put it differently, to use the natural resources provided by the outdoor environ-ment as much as possible. In order to achieve ‘constant conditions’ inside the building, the outdoor impacts that are continuously changing need to be fi ltered, e.g. the light transmission should be maximum when there is only little daylight available or minimized when solar radiation is at its peak. Looking at the principal scenarios mentioned above, this means:

• Transmission of solar radiation with diffuse sky conditions and during heat demand

• Reduction of solar transmission in case of direct sunlight and during cooling load

• Decrease the loss of heat in case of heat demand• Increase the loss of heat in case of cooling load

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• Increase the heat entry during heat demand• Decrease the heat entry during cooling load.

The above indicates that a facade needs to be very ‘responsive’ to outside conditions in order to maximize the use of light, heat and fresh air that might be needed inside to naturally fulfi l comfort requirements and reduce the energy consumption of a building. In terms of physical properties this means looking for materials or elements in a building envelope that are able to:

• Change the solar factor• Vary the light transmission• Alter the U-value• Open and close for natural ventilation.

We will now explore how textile materials can change the solar factor, light transmission, U-value and be opened and closed for natural ventilation. This gives a feeling on what textiles can contribute to a facade being ‘responsive’ to its outside environment and inside needs, and indicates the possibilities of saving operational energy, costs and resources in general.

13.4 Contributions of textile materials to reduce the

operational energy demand, and comparisons

with examples from nature

This section reveals opportunities that textile applications provide, espe-cially with regard to the aforementioned need for variable solar factors and daylight penetration, natural ventilation and heat transmittance to enhance possibilities for energy savings and compares these with examples from nature.

13.4.1 Avenues to alter the light transmission

Fixed and movable shading systems and daylight devices exist. Whilst the fi rst category is cheaper in general, the latter sort is more reactive, thus having more possibilities for saving energy and serving comfort require-ments better.

An example of a well-designed shading system in nature can be found in the world of plants: the cactus. Cacti commonly grow in arid and hot envi-ronments and are native to areas of southern Canada and South America, having also been introduced into Australia and Sri Lanka. Cacti can handle a range of temperatures from below freezing up to around 50°C (Mares, 1999). Figure 13.2 shows a cactus having large fl eshy ribbed stems where water is stored and the photosynthesis process takes place. The vertical ribs surrounding the cactus provide a self-shading mechanism. In order to cope

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with the high temperatures it is exposed to, the angle and depth of the ribs are ‘designed’ to shade the surface over the rest of the plant throughout the day. ‘The spines protect the succulent tissues of the cactus from poten-tial herbivores and help prevent the cactus from overheating by reducing incident solar radiation and providing a boundary layer around the plant that reduces convective heat transfer (transfer of heat from the heated environment to the plant)’ (Mares, 1999). In addition, a light-coloured waxy layer covers the skin and refl ects some light, protecting the stem from water loss. Throughout the course of evolution, the cactus body has increasingly thickened and reduced its surface area, thereby shielding its body from its scorching environment (Schwartz et al., 1999). Cacti adapted over time and responded to their harsh climate.

Similar to the above example from nature is a textile shading system proposed by the New Zealand architects Jasmax for the Sylvia Park Offi ces project in Auckland. Figures 13.3 and 13.4 show the building and shading system that is made of honeycomb semi-transparent tension membrane fabric sunshade, suspended 1000 mm out from the curtain wall glazing on the west facade of four offi ce buildings. Details of the system can be seen in Fig. 13.5 (Jasmax, 2010). Like the fl eshy ribs of the cactus mentioned

13.2 Shading effect of the fl eshy ribs of a cactus.

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13.3 Proposed honeycomb semi-transparent tension membrane fabric sunshade at the Sylvia Park Offi ces, Auckland, New Zealand (Jasmax, 2010).

13.4 Proposed architectural design for Sylvia Park Offi ces, Auckland, New Zealand (Jasmax, 2010).

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above, the depth of the system shades the facade behind, thus reducing solar penetration and cooling loads during summer. The fi ligree system design as well as the perforation of the mesh protects from low-level western sun, allows penetration of diffuse light during overcast skies and still main-tains views to the outside.

Another shading system is the roof construction of the outdoor plaza at the Hawthorn campus of the Swinburne University in Melbourne, Australia. The architects DesignInc in Melbourne used infl atable ETFE cushions that cover the plaza between two buildings. Figure 13.6 shows the pillows, approximately 3.5 × 20 m, supported from a lightweight steel structure free-spanning between two existing buildings that offers weather protection for a multipurpose space (DesignInc, 2010). A vertical ‘wall’ underneath the ETFE cushions was designed to shield the occupant at ground level from fi erce hot northerly winds. Glass is used up to 3 m, followed by an ETFE cushion and a 70% open stainless steel mesh to the underside of the arching roof for ventilation purpose. To enhance ventilation, glass louvres can be opened at the bottom of the glass wall (see Fig. 13.7). Sun protection is offered by 20% coverage of small printed dots to the upper surface of the cushions. This seems suffi cient due to a high-rise building at one side of the roof structure casting a shadow over the system. In a situation of higher

13.5 Proposed detail of the textile shading system for Sylvia Park Offi ces, Auckland, New Zealand (Jasmax, 2010).

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solar exposure a more fl exible shading system could have been derived from a three-layer cushion. By printing overlapping graphics on multiple layers, the solar transmission can be altered by either increasing the pres-sure in the upper or lower chamber; see Fig. 13.8 (Vector Foiltec, 2010; LeCuyer, 2008).

The applications above show possibilities for shading and light penetra-tion through different textile materials. The option to print a second layer within the cushion is a unique system that allows reaction to various light intensities of the sky, thus being a ‘responsive’ device in itself. To achieve this responsiveness in a vertical facade is possible in general, especially in areas where a slight distortion of the view to the outside can be tolerated. This could be either in multi-storey atria or, on a smaller scale, in building

13.6 ETFE roof construction, Swinburne University, Melbourne, Australia.

13.7 Air-intake element, Swinburne University, Melbourne, Australia.

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facade sections that would normally be opaque, such as spandrel areas. Other areas of application could be those that are directed to the sky, e.g. parts directly below the ceiling or above a light shelf.

13.4.2 Examples of variable thermal performance improvements

In general, thermal improvements mean the minimization of the heat fl ux that is normally represented by the U-value. A constant and low heat transmission results in the heat built up inside being ‘trapped’ due to inter-nal heat loads. This makes it important to consider possibilities of ventilat-ing the building, especially in a situation where the outside temperatures are suitable. Because of changing outside conditions, natural ventilation is not always possible, or the building simply does not provide window open-ings, which underpins the need for a variable U-value to balance the indoor temperature naturally.

The principle behind many materials that insulate, thereby decreasing the U-value, is the creation of air cavities in order to minimize the heat movements. One example from nature working with this principle is the penguin. This animal offers a model for dynamic insulation providing excel-lent insulation in air as well as water. Figure 13.9 indicates feathers of penguins being ‘fi lamentous and forming a hall layer around the body in order to control their own heat and cooling loads’ (AskNature, 2009). They are not arranged in tracts, as in other birds, but are packed over their surface instead. The feathers are short and stiff and comprise an outer ‘pen-naceous’, or vane, region and a downy inner ‘after-feather’ (Dawson et al., 1999). Muscles on the shaft of the feather can pull them down into a water barrier when under water or stick them up when back on land and sur-rounded by air. The inner fur therefore traps the heat built up inside the

13.8 Overlaying graphics on a three-layer ETFE cushion (Vector Foiltec, 2010).

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body of the animal and the outer feather structure reduces the heat loss even further (see Fig. 13.9(c)). The ‘system’ can thereby either trap air or release it – a highly responsive element that can alter its ability to transmit heat according to its need (Dawson et al., 1999). This principle can be applied to a building that also creates heat inside, due to the internal loads and – depending on the climate zone it is situated in – encounters heat loss that might need to be reduced passively.

A built example that uses a similar principle in its envelope is the Baader Wertpapierhandelsbank in Unterschleißheim, Germany. The PTFE glass-fi bre mesh fi xed on aluminium frames builds a second envelope creating an air cavity between the outer and inner facades, as shown in Fig. 13.10 (Colt, 2010). Similar to the penguin, this can reduce the heat transmission in winter if the air temperature in the cavity is higher than outside. In summer, obviously, the system needs to be opened to prevent overheating of the air cavity. This risk is already diminished due to the perforation of the material and further eliminated by the possibility of opening the fabric wings to enhance ventilation (see Fig. 13.11). In addition, the wings also control the light penetration of the building during daytime.

Another interesting example in this regard is the Gerontology Technology Centre in Bad Tölz, Germany. The spiral shape of the building has a double-skin facade in front of the open walkways made of ETFE fi lm curving in two directions and spanning over four storeys, as presented in Fig. 13.12. The single-layer membrane forms a buffer between the building

(a)

(b)

(c)

13.9 Simplifi ed penguin feather: (a) straight and (b) ‘insulating’ position, with (c) air pockets indicated as circles, after AskNature (2009) and Dawson et al. (1999).

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13.10 Baader Wertpapierhandelsbank, Unterschleißheim, Germany (Colt, 2010).

13.11 Opening of the textile lamellars, Baader Wertpapierhandelsbank, Unterschleißheim, Germany (Colt 2010).

itself and the exterior. This zone is heated up by solar radiation and dimin-ishes the heat losses in winter when ambient air temperatures would be lower. In summer, additional internal screens protect from excessive solar gains and the sensor-controlled vents open during the night to cool down the activated concrete slabs of the walkways (Jeska, 2008).

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13.4.3 Textile and biomimicry contributions to infl uence natural ventilation

To further inspire ideas for energy-effi cient solutions, another example from nature is provided – the burrows of black-tailed prairie dogs. Figure 13.13 indicates the ventilation of an underground system that black-tailed prairie dogs appreciate living in (Nachtigall, 1997; Hoogland, 1995). As they respire, carbon dioxide and other gases associated with living underground build up. To improve their living conditions they construct their burrows in a way that utilizes the climatic conditions. As air passes over the ground, the rising and sinking of the air over the mounds they make results in lower air pressure in the burrow, causing the pulling of air into the burrow and forcing out stale air. In order to enhance the air to naturally ventilate down into the burrows, the entrances are shaped in a volcano-like manner. The

13.12 Gerontology Centre, Bad Tölz, Germany (Jan Cremers, Munich, Germany).

13.13 Ventilation principle in a burrow of black-tailed prairie dog, after Nachtigall (1997) and Hoogland (1995).

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constant exchange of air provides the prairie dog with comfortable living conditions underground (Hoogland, 1995).

Old buildings already took advantage of this principle, as can be seen in Fig. 13.14, showing a cistern cooling system (Nachtigall, 1998). The dimen-sions and form of the upper part plays an important role in the ability to ventilate and therefore cool the buildings. This can be compared with an example of current architecture. Sauerbruch Hutton Architects designed the GSW building in Berlin, Germany, with a ‘wind roof’ on top of a 22-storey curved high-rise building (see Fig. 13.15). At the height of 81 m, the building is crowned with the ‘wing’; a curved steel construction covered by a textile membrane. The form creates a negative aerodynamic pressure supporting the natural current in the double-skin facade on the basis of the so-called ‘Venturi effect’. It is a vital component for the energy concept of the building. In combination with the air inlet elements at the bottom of the facade, the wing extracts the air from the multi-storey double-skin facade. It needs to be carefully designed in order to work for the most predominant wind directions as well as with very low velocities to prevent overheating in the cavity of the facade (GSW, 2000).

Similar to the burrows, a solar chimney is a tube that needs air velocity to function properly. The solar radiation heats up the air in the cavity, inducing the rise of the air, which is further enhanced by an appropriately designed upper air outlet. Obviously, this is supposed to be at the highest position of the building to extract exhaust air in a natural way and without additional use of fans.

Due to the high light transmittance of PFTE and ETFE a solar chimney can be covered with these textile materials, as shown in Figs 13.16 and 13.17.

(a) (b)

13.14 Simplifi ed ventilation principle of (a) a cistern, and (b) the double-skin facade of the GSW building, after Nachtigall (1998) and GSW (2000).

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13.15 Textile ‘wing’ on the roof-top of the GSW Building, Berlin, Germany.

13.16 Elevation of the proposed design for the RMIT (Royal Melbourne Institute of Technology), Melbourne, Australia (Hoe, 2009).

This is part of a proposal for a refurbishment of a RMIT University (Royal Melbourne Institute of Technology) building in Melbourne, Australia (Hoe, 2009). The use of these solar chimneys reduces the amount of glass in the facade thereby diminishing the cooling load. The depth of this chimney design intends to direct the light into the rear of the rooms.

The temperature of the air built up by solar radiation in the chimneys can be infl uenced by either a pattern applied to the foils (as previously mentioned) or the openings of the system’s outlet at the top of the building. In winter, the system would be closed and the accumulated heat helps to reduce the heat loss. Stored heat can be redirected into the building to keep

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13.17 Functionality of the proposed solar chimney for the RMIT (Royal Melbourne Institute of Technology), Melbourne, Australia (Hoe, 2009).

the heating load down, e.g. during the night. The heat built up in the cavity during the day needs to be controlled, as the internal surface temperature should neither cause thermal discomfort, nor increase cooling loads. In summer, the system would therefore be as open as possible; the heated up thermal mass can then buffer temperature peaks and act as a heat sink, as shown in Fig. 13.18 (Hoe, 2009).

13.5 Deliberations on future applications

The overview of the survey in Australia indicated challenges for textiles becoming a mainstream building material. The issues related to operational energy were dealt with by providing general guidelines to be considered

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for the planning of an energy-effi cient facade. In order to minimize the operational energy demand while still providing comfortable conditions, a responsive facade needs to be able to change the solar, heat and air trans-mission according to the various outdoor environmental conditions.

The last three sub-sections on textile applications showed three examples from nature and compared these with three international buildings and three projects from Australia and New Zealand with regard to their ability to alter the solar, heat and air transmission into the building.

The daylight ingress can be varied by using either mesh or foil structures. The examples showed that a mesh can be applied in a fi xed or movable way, thereby changing the light transmission according to its form and/or position. The grid of the mesh can be adjusted as needed for glare protec-tion. The three-layer ETFE cushions have the possibility of incorporating a movable layer, thereby altering solar ingress. However, it needs to be

(a) (b)

13.18 Proposed solar chimney for the RMIT (Royal Melbourne Institute of Technology), Melbourne, Australia: (a) solar wall; (b) heat sink (Hoe, 2009).

��



taken into consideration that the pumping of air from one cavity to the next is time consuming. This suggests the materials’ use for areas in a building where certain slow luminance changes can be accepted, such as atria, halls, winter gardens, etc.

The principle behind thermal resistance can be called ‘building up air cavities’. Cushions are cavities in themselves and the more layers, the more cavities, the better the U-value. Materials such as mesh can also be used, although its holes infl uence the heat transmission. Two movable layers behind each other could open or close, thus infl uencing the heat transmis-sion according to the internal needs of the building.

Natural ventilation is airfl ow that can be induced either by solar radiation or through openings in combination with the built form. Examples showed that outlet or inlet elements can be made of foils and solar chimneys can be covered with larger-scale cushions. The variable transmission through a second printed foil within a three-layer component can even regulate the temperature inside by changing the solar transmission.

Textiles can support the ambition of a responsive building envelope to save operational energy, as the discussion above has indicated. Still, areas exist that need further investigation to spread suffi cient information to designers and construction planners, to provide them with the necessary security in planning to use textiles. These areas are embodied energy and cost comparisons to other transparent or translucent elements. Life-cycle costing of these materials is another fi eld that needs further investigation. Although constant pumping and refi lling of air into the cushions does not seem to consume signifi cant energy, precise life-cycle comparisons can provide planners with additional decision-making support. This research is currently ongoing and being undertaken by the author at The University of Melbourne.

From a design concept point of view the variety of textile structures offers great opportunities for designers. As each textile material has its own strengths and challenges, it might be helpful to deliberately think of not using one specifi c material for an entire vertical facade, but rather think of other textile materials as well and place them on the building according to their strengths. A closed PTFE fi lm for a multi-storey double-skin facade, for example, might increase the cavity temperature depending on the overall height if not ventilated in certain areas, whereas a textile mesh could naturally ventilate the cavity and prevent overheating without the need for air intake and air outlet elements. This obviously is highly related to the conditions the building provides and the aesthetic appearance the architect has in mind.

Application ideas have been provided for vertical facades, such as ETFE for solar chimneys, facade areas and others. Framed and smaller-sized elements could accelerate the degree of creativity and design freedom

��



of the architect, as they might become independent and ready-to-use components.

Even more applications of textile materials can be seen to support the sustainable upgrading of existing buildings. For example, the area of ‘re-skinning’ buildings can have an enormous infl uence on the overall greenhouse gas emissions of a country. Lower-grade buildings make up approximately 80% of the Australian offi ce building stock and are there-fore currently a focus on the sustainability agenda (Langdon, 2009).

No matter whether textile materials are applied to new or existing projects, the application needs to be an integral part of the energy concept of a building in order to be sustainable. Biomimicry is a fi eld where holistic approaches can be perceived and can form a platform from which to learn and create new ideas, hopefully securing our life on this planet.

13.6 References

AskNature (2009), www.asknature.org/penguins (accessed 21.4.2009)Bartenbach, C (2001), Von der Helligkeit zur Wahrnehmung, published by

Bartenbach Lichtlabor GmbH, Aldrans-Innsbruck, AustriaBehling S, Behling S (1996), Sol Power – The Evolution of Solar Architecture,

Munich and New York, Prestel, p. 31Colt (2010), ‘Baader Wertpapierhandelsbank, Unterschleißheim’, case history,

www.coltgroup.com (accessed 20.2.2010)Dawson C, Vincent J, Jeronimidis G, Rice G, Forshaw P (1999), ‘Heat transfer

through penguin feathers’, Journal of Theoretical Biology, Vol. 199, No. 3, pp. 291–295

DesignInc (2010), Information from the architects DesignInc, Melbourne, AustraliaGhisi E, Tinker J (2001), ‘Optimising energy consumption in offi ces as a function

of window area and room size’, Seventh International IBPSA Conference, Building Simulation, pp. 1307–1314

GSW (2000), ‘In the skies of Berlin: The GSW offi ce block’, information fl yer of the GSW, 4/2000, GSW, Berlin, Germany

Harvey, D (2009), ‘Reducing energy use in the building sector: measures, costs and examples’, Energy Effi ciency, Vol. 2, pp. 139–163

Hoe, F (2009), ‘Soft hard facade’, unpublished report, subject ‘Facade Design and Performance’, Faculty of Architecture, Building and Planning, The University of Melbourne, Australia

Hoogland, J (1995), The Black-Tailed Prairie Dog – Social Life of a Burrowing Mammal, University of Chicago Press

IPCC (2007), ‘Climate Change 2007: Synthesis Report’, IPCC Fourth Assessment Report (AR4), IPCC, Geneva, Switzerland

Jasmax (2010), Information from the architects Jasmax, Wellington, New ZealandJeska S (2008), Transparent Plastics – Design and Technology, Basel, BirkhäuserLangdon, D (2009) ‘Retrogreening offi ces in Australia’, Research Report, http://

www.davislangdon.com/upload/StaticFiles/AUSNZ%20Publications/Technical%20Reports/Retrogreening-offi ces-in-Australia.pdf (accessed 6.6.2009)

��



Lau, K (2009), ‘The application of textile facades to energy effi cient buildings in Australia’, research project supervised by Associate Professor Eckhart Hertzsch, Faculty of Architecture, Building and Planning, The University of Melbourne, Australia

LeCuyer A (2008), ETFE – Technologie und Entwurf, Basel, BirkhäuserMares, M (1999), Encyclopedia of Deserts, University of Oklahoma Press, Norman,

OK, USANachtigall, W (1997), Vorbild Natur – Bionik-Design für funktionelles Gestalten,

Berlin, SpringerNachtigall, W (1998), Bionik – Grundlagen und Beispiele für Ingenieure und

Naturwissenschaftler, Berlin, SpringerNicol, J, Humphreys, M (2002), ‘Adaptive thermal comfort and sustainable thermal

standards for buildings’, Energy and Buildings, Vol. 34, pp. 563–572OECD (2003), Environmentally Sustainable Buildings – Challenges and Policies,

OECD Publications Service, Paris, France, pp. 20–24Pedersen, Z (2008), ‘Biomimetic approaches to architectural design for increased

sustainability’, Sustainable Building Conference, Auckland, New ZealandSchwartz, A, Patriquin, D, Mills, C, Mills, A (1999), ‘Biology of cacti’, http://cactus.

biology.dal.ca/biology.html (accessed 20.4.2009)Vector Foiltec (2010), company brochure, Victoria, Australia

13.7 Appendix

Sylvia Park Offi ces (Fig. 13.3; Fig. 13.4; Fig. 13.5)

Location: Auckland, New ZealandArchitects: JasmaxSituation: Design stageMembrane structure: Tension membrane fabric sunshade

Swinburne University (Fig. 13.6; Fig. 13.7)

Location: Melbourne, AustraliaArchitects: DesignInkSituation: CompletionMembrane structure: ETFE layer cushions for roof construction and verti-

cal facade

Baader Wertpapierhandelsbank (Fig. 13.10; Fig. 13.11)

Location: Unterschleißheim, GermanyArchitects: Baader & Schmid ArchitectsSituation: CompletionMembrane structure: PTFE glass-fi bre mesh

��



Gerontology Technology Centre (Fig. 13.12)

Location: Bad Tölz, GermanyArchitect: SiegertSituation: CompletionMembrane structure: One-layer ETFE fi lm

GSW Building (Fig. 13.15)

Location: Berlin, GermanyArchitects: Sauerbruch Hutton ArchitectsSituation: CompletionMembrane structure: Textile membrane on curved roof construction

RMIT (Royal Melbourne Institute of Technology) (Fig. 13.16; Fig. 13.17; Fig. 13.18)

Location: Melbourne, AustraliaArchitect: Student, The University of MelbourneSituation: Proposed designMembrane structure: ETFE cushions for solar chimney facade

��


398

14Challenges in using textile materials in

architecture: the case of Australia

E. HERTZSCH and K. LAU, University of Melbourne, Australia

Abstract: This chapter is about understanding the contribution that textile materials as a facade cladding can provide to an energy-effi cient building, and why Australian buildings have yet to embrace their use. A review of literature identifi es critical energy-effi cient facade attributes, and an analysis of the performance of textiles provides a summary comparison to traditional glazed facades. Major architectural fi rms in Australia were surveyed as to their knowledge of textiles as facade materials, their opinions on obstacles on the wider use of this material, and how architects could be encouraged to apply them.

Key words: fabric facade, textile materials, energy effi ciency, fabric and glass cost comparisons.

14.1 Introduction

The contribution of the built environment to global greenhouse gas emis-sions has become a major cause of climate change. Current research has estimated that building energy consumption has become one-third of the total energy consumption in the world. The building sector accounts for 25–40% of fi nal energy consumption in OECD countries (OECD, 2003).

The energy to operate a building represents the largest component of life-cycle energy use. Recent studies have shown that in a typical building with a service life of 50 years, operational energy accounts for 85–95% of total energy use (Thormark, 2006). It is thus a crucial component of an energy-effi cient building that it reduces the demand on energy-intensive building services. Strategies for reducing the operational energy used in a building’s lifetime should fi rst and foremost be considered in the design process (Cole and Kernan, 1996).

The negative impact the building and construction industry has on the environment needs to be addressed in all future buildings, and in the exist-ing building stock. Focusing on construction of high-performance buildings, through implementation of effective building systems and design, will not only result in energy-cost savings, but with improved daylighting and down-

��

Challenges in using textile materials in architecture 399


sized building systems for ventilation, heating and cooling, also enhance worker productivity (Harvey, 2009).

Choice of material is a major determinant of the energy required in construction and operation of buildings and consequential environmental impact. Low embodied energy, minimal environmental impact, longevity, compatibility with other building materials, and maintenance requirements over the lifetime of the building are important issues when choosing a build-ing material (Dimoudi and Tompa, 2008).

Fabrics or textiles are becoming an increasingly popular choice of build-ing material as they offer highly expressive architectural and engineering solutions. According to Simmonds (2006), they bridge the gap between the transitory and the permanent, between performance and sculpture, in what is an attractive mix of the aesthetic and the functional. Textiles in building have been widely used in atria and as an alternative roofi ng material around the world.

Textiles used as fabric facades are commonly a coated mesh. This allows a view out and reduces energy consumption while providing solar protection (Armijos, 2008). The most common types are PVC-coated polyester manufactured into a coated or extruded product, PTFE (poly-tetrafl uoroethylene or Tefl on) coated fi breglass mesh, and ETFE (ethylene-tetrafl uoro ethylene) foils.

14.2 Aim, objectives and methodology of the study

The study had three main objectives:

1. To investigate the contribution of textile facades to energy effi ciency and its practical application to buildings in Australia

2. To identify reasons why textile facades are not yet being utilized as a mainstream construction system for sustainable buildings in Australia

3. To identify ways to encourage designers to apply textiles, such as ETFE infl ated foil cushions and PTFE-coated fi breglass fabric, to improve the energy effi ciency of buildings in Australia.

In addressing objectives 2 and 3, in particular, a number of questions needed answering:

• How much do Australian industry professionals know about the use of textiles in building?

• What sort of buildings are they suitable for?• Why has the Australian construction industry yet to adopt textile

facades in creating energy-effi cient buildings?• How can industry professionals be encouraged to apply textiles to

improve the energy-effi cient performance of a facade in Australia?

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In order to evaluate the knowledge of architects, the current literature was reviewed. It revealed that for the energy-effi cient facade attributes textiles, such as ETFE and PTFE, do offer considerable benefi ts to energy-effi cient building design. A comparison table indicating the attributes of ETFE, PTFE and glass is shown in Table 14.1.

This overview is not intended to be complete or fully comprehensive. It is designed to frame a basis for the architects’ interviews and compare their answers to some of the information found in the literature.

The interview was undertaken to determine whether the information obtained from literature was well recognized and refl ected in the Australian design industry and, if not, to identify a general consensus about the suit-ability of textile facades in Australia, and why they are rarely applied to energy-effi cient buildings.

Major architectural fi rms based in Australia were chosen as the sample for the study. A suitable sample was selected from the Australian Institute of Architects’ website with at least 30 staff. Twelve individual architects of various ages and both genders were interviewed. Approximately 25% of the fi rms had practices in other Australian states. Although the number is relatively small, these fi rms represent the major architects in Australia and it is believed that they well refl ect the country’s ‘state of the art’ architec-tural practices.

14.3 Results of the interview

The interview questionnaire consisted of three sections. Parts A and C were open discussion questions, while Part B had structured questions that required the architect to provide an opinion based on a scaled range of options.

14.3.1 Part A – The experience of architects

Part A aimed to understand the individual’s level of experience and background knowledge on facades, energy effi ciency and textiles. These general questions also provided a guideline as to whether or not a specifi c respondent had considered the use of a textile material in a previous project.

As shown in Table 14.2, the individuals had diverse levels of experience. The majority of the architects (42%) had between 10 and 20 years of experi-ence. A clear majority (67%) saw themselves as having a high level of experience in energy-effi cient building and facade design, but more than half (58%) considered their level of knowledge on textiles as low; in con-trast, only 8% considered their knowledge on textiles as high.

��


Tab

le 1

4.1

Co

mp

aris

on

mat

rix

of

the

ener

gy-

effi

cien

cy a

ttri

bu

tes

of

ET

FE,

PT

FE a

nd

do

ub

le-g

laze

d u

nit

s; r

efer

ence

s: 1

= A

rch

iten

La

nd

rell

(200

9),

2 =

Hig

hte

x (2

009)

, 3

= Fa

bri

c A

rch

itec

ture

(20

08),

4 =

GJa

mes

Gla

ss (

2009

), 5

= S

hie

lds

(200

2),

6 =

Ro

bin

son

-Gay

le

et a

l (2

001)

, 7

= R

awlin

son

s (2

009)

, 8

= M

acle

od

(20

10),

9 =

Sto

kes

(199

8),

10 =

LeC

uye

r (2

008)

, 11

= T

ann

o (

1997

), 1

2 =

Wri

gh

t (2

009)

Att

rib

ute

sE

TFE

in

fl at

ed c

ush

ion

s (t

rip

le l

ayer

ed)

PT

FE c

oat

ed fi

bre

gla

ss

fab

ric

PT

FE f

abri

cD

ou

ble

gla

zed

un

it

Co

mm

ents

Su

sta

inab

ilit

y i

ssu

es

Lig

ht

tran

smit

tan

ceA

pp

roxi

mat

ely

90%

m

axim

um

(83

–88%

of

UV

sp

ectr

um

; sc

atte

red

lig

ht

12%

)2,8

7–29

%,

dep

end

ing

on

fa

bri

c th

ickn

ess.

T

ypic

ally

65–

75%

is

refl

ecte

d a

nd

up

to

8%

ab

sorb

ed3

20%

(va

riab

le)8

78%

(81

% s

ing

le

gla

zin

g)4,

8E

TFE

has

cu

sto

mis

able

lig

ht

tran

smis

sio

n

pro

per

ties

. D

iffe

ren

t le

vels

can

be

ach

ieve

d b

y p

atte

rns

on

th

e su

rfac

e o

f o

ne

or

mo

re l

ayer

s o

f th

e sy

stem

. T

he

den

sity

an

d p

atte

rn o

f th

e ‘p

rin

t’ d

efi n

es

the

leve

l o

f lig

ht

tran

smis

sio

n.

Pat

tern

s ca

n a

lso

be

add

ed t

o g

lass

th

us

pro

vid

ing

su

n a

nd

gla

re p

rote

ctio

n8

Su

n a

nd

gla

re

pro

tect

ion

Litt

le p

rote

ctio

n:

Frit

p

atte

rns

can

be

add

ed

to p

rovi

de

gla

re

pro

tect

ion

. M

ova

ble

la

yers

can

be

inte

gra

ted

to

co

ntr

ol

ligh

t tr

ansm

issi

on

an

d s

ola

r g

ain

Go

od

sh

adin

g a

nd

re

sist

ance

to

UV

sp

ectr

um

Go

od

sh

adin

g

qu

alit

ies

(SH

GC

0.

18)

No

pro

tect

ion

. C

an b

e im

pro

ved

by

add

ing

p

atte

rns,

su

n s

had

es,

etc

U-v

alu

e1.

9 W

/m2 K

(5.

1 W

/m2 K

fo

r a

sin

gle

lay

er

syst

em)2,

8

4–5

W/m

2 K (

add

itio

nal

la

yers

can

dec

reas

e th

e U

-val

ue)

1

4.6

W/m

2 K2.

7–3.

1 W

/m2 K

(5.

5 W

/m2 K

fo

r si

ng

le g

lass

) h

ori

zon

tal

app

licat

ion

4,8

Gla

ss u

sed

fo

r ve

rtic

al a

pp

licat

ion

s ca

n

hav

e ve

ry l

ow

U-v

alu

es;

esp

ecia

lly t

rip

le

gla

zed

un

its

or

do

ub

le g

laze

d u

nit

s w

ith

g

as fi

llin

gs

Em

bo

die

d e

ner

gy

27 M

J/m

2 6

All

arch

itec

tura

l fa

bri

cs

hav

e b

een

fo

un

d t

o

hav

e a

low

er

emb

od

ied

en

erg

y co

mp

ared

to

tr

adit

ion

al m

ater

ials

(s

uch

as

gla

ss)11

,12

All

arch

itec

tura

l fa

bri

cs h

ave

bee

n f

ou

nd

to

h

ave

a lo

wer

em

bo

die

d e

ner

gy

com

par

ed t

o

trad

itio

nal

m

ater

ials

(su

ch

as g

lass

)11,1

2

300

MJ/

m2

5C

om

par

iso

ns

of

emb

od

ied

en

erg

y fo

r fo

il st

ruct

ure

s an

d g

lass

alt

ern

ativ

es s

ho

uld

al

way

s ta

ke t

he

emb

od

ied

en

erg

y o

f th

e su

pp

ort

ing

str

uct

ure

in

to c

on

sid

erat

ion

; a

‘sys

tem

as

a w

ho

le a

pp

roac

h’

is

view

ed a

s th

e m

ost

ap

pro

pri

ate

on

e

Ava

ilab

le o

pti

on

sA

dd

itio

n o

f fr

it p

atte

rns,

co

atin

gs

and

lig

hti

ng

ef

fect

s

Sta

nd

ard

wh

ite;

co

lou

red

fab

rics

av

aila

ble

Co

lou

red

fab

rics

ar

e av

aila

ble

Co

atin

gs,

co

lou

r ti

nts

an

d

oth

er o

pti

on

s, e

.g.

infi

lls

��


Att

rib

ute

sE

TFE

in

fl at

ed c

ush

ion

s (t

rip

le l

ayer

ed)

PT

FE c

oat

ed fi

bre

gla

ss

fab

ric

PT

FE f

abri

cD

ou

ble

gla

zed

un

it

Co

mm

ents

Rec

ycla

bili

ty8

Yes

Yes

Yes

Yes

ET

FE i

s n

ot

a p

etro

chem

ical

der

ivat

ive

and

is

per

mit

ted

un

der

th

e M

on

trea

l T

reat

y.

No

so

lven

ts a

re u

sed

in

th

e m

anu

fact

ure

o

f th

e ra

w m

ater

ials

. It

is

fully

rec

ycla

ble

Str

uctu

ral

issu

es

Un

it s

ize

Typ

ical

cu

shio

n s

ize

is 3

×

6 m

; u

p t

o 2

5 ×

3.5

m (

sin

gle

lay

er

syst

ems

can

be

man

ufa

ctu

red

in

to

alm

ost

an

y si

ze)1,

10,1

1

Up

to

160

0 m

2 fo

r a

sin

gle

pan

el1

Var

iab

le;

up

to

4 m

fl

at s

pan

8T

ypic

al g

lass

pan

el s

ize

is

in a

ran

ge

of

1 ×

4 m

9D

ue

to s

mal

ler

pan

el s

izes

an

d t

he

wei

gh

t o

f g

lass

, th

e su

pp

ort

str

uct

ure

in

gen

eral

n

eed

s to

be

mo

re s

ub

stan

tial

Cu

sto

m p

anel

si

ze8

Yes

Yes

Yes

Yes

; h

igh

co

stFa

bri

c sy

stem

s h

ave

a va

riab

le s

pan

as

span

is

a fu

nct

ion

of

the

shap

e o

f th

e sy

stem

Wei

gh

t1

kg/m

2 8

1 kg

/m2

1,8

1 kg

/m2

1,8

30 k

g/m

2 (6

mm

gla

ss

wei

gh

s 15

kg

/m2 )8,

9E

ven

a s

ing

le g

lass

pan

e u

sed

fo

r a

roo

f co

nst

ruct

ion

can

be

32 k

g/m

2 if

it i

s sa

fety

gla

ss8

Pri

mar

y st

ruct

ure

(s

teel

)25

–35

kg/m

2 8

30–4

0 kg

/m2

830

–40

kg/m

2 8

45–6

5 kg

/m2

8T

he

sup

po

rtin

g s

tru

ctu

re f

or

ET

FE s

ho

uld

al

way

s b

e ta

ken

in

to c

on

sid

erat

ion

w

hen

co

mp

ared

wit

h a

gla

ss a

lter

nat

ive

Sp

eed

an

d e

ase

of

inst

alla

tio

n8

Go

od

Go

od

Go

od

Mo

der

ate–

po

or

Fab

rics

an

d E

TFE

sys

tem

s ar

e u

sual

ly v

ery

qu

ick

to i

nst

all

as t

hey

are

lig

htw

eig

ht,

la

rgel

y p

refa

bri

cate

d o

ff s

ite

and

are

‘s

oft

’ te

chn

olo

gie

s. G

laze

d s

olu

tio

ns,

w

hile

als

o p

refa

bri

cate

d o

ff s

ite

req

uir

e ex

ten

sive

pre

par

atio

n o

f in

terf

aces

to

en

sure

lo

ng

ter

m p

erfo

rman

ce.

Gla

zed

so

luti

on

s al

so r

equ

ire

spec

ial

inst

alla

tio

n

tech

niq

ues

to

acc

om

mo

dat

e th

e in

crea

sed

sel

f w

eig

ht

of

the

syst

em

Tab

le 1

4.1

Co

nti

nu

ed

��


Att

rib

ute

sE

TFE

in

fl at

ed c

ush

ion

s (t

rip

le l

ayer

ed)

PT

FE c

oat

ed fi

bre

gla

ss

fab

ric

PT

FE f

abri

cD

ou

ble

gla

zed

un

it

Co

mm

ents

Pro

tecti

on

issu

es

Fire

per

form

ance

Low

fl a

mm

abili

ty a

nd

se

lf e

xtin

gu

ish

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. Fi

re a

nd

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will

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use

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e fo

il to

mel

t an

d c

reat

e a

ven

t1

No

n c

om

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le;

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on

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igh

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per

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res.

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c ca

n w

ith

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d

tem

per

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res

up

to

10

00°C

, se

ams

up

to

27

0°C

1,8

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om

bu

stib

le;

po

ssib

ility

of

fl am

ing

dro

ps8

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n c

om

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will

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ack

at 1

10°C

5A

ll cl

add

ing

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eria

ls w

ill h

ave

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es w

ith

fi

re.

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n a

vera

ge

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ss s

yste

ms

are

no

t d

esig

ned

to

wit

hst

and

ext

rem

ely

hig

h

tem

per

atu

res8

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ise

tran

smis

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nH

igh

. R

ain

no

ise

can

be

sup

ress

ed w

ith

an

ad

dit

ion

al l

ayer

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h.

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n n

ois

e ca

n

be

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ress

ed w

ith

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ad

dit

ion

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ayer

1,8

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h r

ain

an

d

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ic n

ois

e tr

ansm

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8

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. In

gen

eral

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r p

erfo

rmin

g t

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te

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n s

up

pre

ssio

n s

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s av

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ost

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r E

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tem

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ista

nce

to

d

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e/re

pai

r o

pti

on

s

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ista

nt

to i

mp

act

dam

age

fro

m b

lun

t b

ut

no

t sh

arp

ob

ject

s;

ind

ivid

ual

cu

shio

ns

can

be

rem

ove

d a

nd

re

pla

ced

wit

h m

inim

al

dis

rup

tio

n;

min

or

rep

airs

can

be

mad

e w

ith

ou

t re

mo

val

fro

m

the

stru

ctu

re

Res

ista

nt

to i

mp

act

dam

age

fro

m b

lun

t b

ut

no

t sh

arp

o

bje

cts;

sm

all

cuts

ca

n b

e re

pai

red

wit

h

glu

e-o

n p

atch

es.

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e te

ars

req

uir

e sp

ecia

list

rep

air

wit

h

ho

t ai

r w

eld

ers.

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div

idu

al p

anel

s ca

n b

e re

mo

ved

an

d

rep

lace

d i

n a

sy

stem

. R

esis

ten

t to

m

ost

gra

ffi t

i p

ain

ts1

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ista

nt

to i

mp

act

dam

age

fro

m

blu

nt

bu

t n

ot

shar

p o

bje

cts.

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atch

rep

air

po

ssib

le1,

8

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ttle

; b

ette

r re

sist

ance

to

sh

arp

ob

ject

s b

ut

no

t im

pac

t d

amag

e,

un

less

tre

ated

to

im

pro

ve s

tren

gth

So

me

man

ufa

ctu

rers

rec

om

men

d p

laci

ng

th

e E

TFE

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tem

ou

tsid

e p

ub

lic r

each

. G

lass

is

also

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scep

tib

le t

o d

amag

e an

d

on

ce d

amag

ed b

eco

mes

qu

ite

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ger

ou

s if

it

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ot

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fety

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ss8

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losi

on

ch

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stic

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il is

a fl

exi

ble

mat

eria

l w

hic

h c

an

take

hig

h s

ho

rt t

erm

lo

adin

g.

Th

is

mak

es i

t a

go

od

pro

du

ct f

or

use

wh

ere

ther

e is

a r

isk

of

exp

losi

on

sS

ecu

rity

8Lo

w–m

od

erat

eLo

wLo

wM

od

erat

e–g

oo

dW

hile

ET

FE c

an b

e ea

sily

dam

aged

if

ther

e is

in

ten

t, t

he

syst

em c

an b

e fi

tted

wit

h a

p

ress

ure

mo

nio

rin

g s

yste

m s

uch

th

at,

in

the

even

t o

f a

dra

mat

ic l

oss

of

pre

ssu

re

an a

larm

will

so

un

d.

Ho

wev

er,

it i

s re

com

men

ded

to

pla

ce E

TFE

sys

tem

s o

ut

of

pu

blic

rea

ch.

Gla

zed

sys

tem

s ca

n

also

be

easi

ly d

amag

ed,

if t

her

e is

in

ten

t

��


Att

rib

ute

sE

TFE

in

fl at

ed c

ush

ion

s (t

rip

le l

ayer

ed)

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FE c

oat

ed fi

bre

gla

ss

fab

ric

PT

FE f

abri

cD

ou

ble

gla

zed

un

it

Co

mm

ents

Lo

ng

evit

y i

ssu

es

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nte

nan

ce8

An

nu

alA

nn

ual

An

nu

alA

nn

ual

A c

om

pre

hen

sive

mai

nte

nan

ce p

rog

ram

me

is r

equ

ired

fo

r th

e E

TFE

sys

tem

to

en

sure

lo

ng

evit

yC

lean

ing

Sel

f cl

ean

ing

; re

com

men

ded

cl

ean

ing

sch

edu

le:

2–3

year

s (e

xter

nal

ly),

5–

10 y

ears

(in

tern

ally

)

Sel

f cl

ean

ing

bu

t d

egra

des

ove

r ti

me

as s

urf

ace

text

ure

h

old

s d

irt;

cle

anin

g

reco

mm

end

ed e

very

2–

5 ye

ars1,

8

Req

uir

es r

egu

lar

man

ual

cle

anin

g;

ho

wev

er d

irt

get

s in

gra

ined

in

to m

emb

ran

e su

rfac

e af

ter

10

year

s8

No

t se

lf c

lean

ing

. C

lean

ing

rec

om

men

ded

ap

pro

xim

atel

y ev

ery

3 m

on

ths4

Gla

ss c

an h

ave

a co

atin

g t

hat

has

a s

elf

clea

nin

g e

ffec

t

Du

rab

ility

/es

tim

ated

lif

esp

an

Ap

pro

xim

atel

y 35

–40

year

s; n

o

deg

rad

atio

n,

loss

of

stre

ng

th1,

8

20–3

0 ye

ars;

th

e U

V

resi

stan

ce i

s h

igh

1,7,

815

yea

rs8

15–3

0 ye

ars7,

8

Mo

neta

ry i

ssu

es

Co

stA

$600

–800

/m2 (

des

ign

, su

pp

ly a

nd

in

stal

l co

sts

for

clad

din

g

syst

em).

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st s

avin

gs

in c

om

par

iso

n t

o

gla

ss c

an o

ccu

r in

re

du

ctio

n o

f st

ruct

ure

, m

ain

ten

ance

, in

stal

lati

on

co

sts,

lif

e cy

cle

cost

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8

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00–6

00/m

2 (d

esig

n,

sup

ply

an

d i

nst

all

cost

s fo

r cl

add

ing

sy

stem

). C

ost

sa

vin

gs

in

com

par

iso

n t

o g

lass

ca

n o

ccu

r in

re

du

ctio

n o

f st

ruct

ure

, m

ain

ten

ance

, in

stal

lati

on

co

sts,

lif

e cy

cle

cost

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8

A$2

50–4

50/m

2 (d

esig

n,

sup

ply

an

d i

nst

all

cost

s fo

r cl

add

ing

sy

stem

)8

A$8

00–1

000/

m2 (

des

ign

, su

pp

ly a

nd

in

stal

l co

sts

for

clad

din

g s

yste

m);

A

$600

–800

/m2 f

or

sin

gle

gla

ss8

Co

sts

for

all

syst

ems

sho

uld

on

ly b

e co

mp

ared

tak

ing

th

e su

pp

ort

ing

st

ruct

ure

in

to a

cco

un

t. D

ue

to t

he

hig

her

w

eig

ht

and

th

e sm

all

un

it s

izes

of

gla

ss

mo

re s

up

po

rt s

tru

ctu

re i

s u

sual

ly

nee

ded

in

co

mp

aris

on

to

ET

FE f

oil

cush

ion

s. O

bvi

ou

sly

this

nee

ds

to b

e co

mp

ared

on

a p

roje

ct b

y p

roje

ct b

asis

Ru

nn

ing

co

stA

pp

roxi

mat

ely

A$3

00–1

000

m2

8N

/AN

/AN

/AIn

gen

eral

dep

end

ing

on

mai

nte

nan

ce

stra

teg

y; s

ee ‘

lon

gev

ity

issu

es’

War

ran

tyA

pp

roxi

mat

ely

25 y

ears

7A

pp

roxi

mat

ely

12

year

s1A

pp

roxi

mat

ely

12

year

s1A

pp

roxi

mat

ely

10 y

ears

4C

an d

iffe

r ac

cord

ing

to

man

ufa

ctu

rer

Tab

le 1

4.1

Co

nti

nu

ed

��



Table 14.2 Architects’ level of experience with regard to energy effi ciency and textiles (ETFE and PTFE)

Question no. Frequency of response

Description/Most common response

Question 1- Number of years as a practising architect

Category 1: 0–10 years 25%Category 2: 10–20 years 42%Category 3: 20–30 years 8%Category 4: >30 years 25%

Question 2: Level of experience on energy effi cient building and facade

design

Category 1: low 0%Category 2: medium 33%Category 3: high 67%

Question 3: Level of knowledge on textiles (ETFE infl ated foil cushions and

PTFE coated fi breglass)

Category 1: low 58%Category 2: medium 33%Category 3: high 8%

Question 4: Consideration of textiles for use on a project

Category 1: Have considered 25% Yes, in the UK; ETFE but not considered suitable structurally

Category 2: Not considered 75% Never suggested, unfamiliar, client restraints

Question 5: When did the architect fi rst hear about textiles as a building

material?

Category 1: Between 1–5 years ago

33% Southern Cross Railway Station (ETFE), Melbourne, Australia; Train stations in Europe

Category 2: Between 5–10 years ago

50% While studying

Category 3: >10 years ago 17% While studying

Question 6: When did the architect fi rst hear about textiles as a permanent

facade system?

Category 1: 1–5 years ago 58% National Aquatic Centre (ETFE), Beijing, China and Rocket Tower (ETFE), Leicester, UK

Category 2: 5–10 years ago 25%Category 3: >10 years ago 17%

��



Of the interviewees, 75% had never considered the use of textiles for a project. Half of these architects explained that the reason for this was that neither the client, nor other parties involved in the design phase, had sug-gested it as a material that could be used.

A majority of the architects (67%) fi rst heard about textiles as a building material 5 to 10+ years ago while they studied at university. A little over half of the interviewees had only heard about textiles being used in perma-nent facade systems between 1 and 5 years ago.

14.3.2 Part B – The architects’ opinions on energy effi ciency-related issues

In this section, architects were asked to rate their opinion of energy-effi cient and textile material properties on a degree or Likert scale. Part B aimed to assess if the information obtained from the literature regarding the relationship between energy-effi cient facades and textiles was well refl ected in the knowledge of Australian architects. These were closed questions with response options in the form of a Rating or Likert scale. This method assigns a score to a response, by asking the respondent to express their degree of agreement or disagreement, attitudes and level of knowledge on a scale from 1 to 5 that was provided. Part B had three dis-tinct subsections:

1. Opinions on the importance of particular energy-effi cient facade mate-rial properties

2. Information on ETFE and PTFE3. Comparison of ETFE and PTFE facade material properties with

double-glazed facades.

Opinions on the importance of particular energy-effi cient facade material properties

The fi rst sub-section explored the degree of importance the designer placed on a particular performance requirement of an energy-effi cient facade material. The items they were asked to rate are:

• Thermal performance and insulation• Sun and glare protection• Daylight• Provision of ventilation• Durability• Low material embodied energy• Recyclability.

��



If ‘of great importance’ was selected, the highest score was allocated, whereas if ‘do not know’ was indicated, the lowest score was allocated. All of these factors are considered important to the performance of a facade in an energy-effi cient building. According to Harvey, the provision of a high-performance facade is the single most important factor in the design of a low-energy building. It increases natural daylighting, reduces heating and cooling loads that mechanical systems would usually account for, and also allows for alternative and low-energy systems to meet the resulting reduced energy loads (Harvey, 2009). Therefore, respondents scored the higher scores in this sub-section if they regarded these factors as crucial for energy-effi cient performance.

Figure 14.1 shows the percentage of opinions from the architects interviewed when being asked to rate how critical seven facade material properties were with regard to an energy-effi cient building design. The ones that were most important for architects were thermal performance, sun and glare protection, daylight and durability. Thermal performance was regarded by everyone as of great importance for an energy-effi cient build-ing. More than 80% of respondents thought that daylight transmission in a facade material was ‘of great importance’ to the energy effi ciency of a building. This result was expected, as maximizing the natural light into a building will not only improve occupant well-being and productivity, but also reduce use of artifi cial lighting and therefore lower the energy con-sumption of a building. A lower percentage (50% and less) seemed to feel that the provision of ventilation and the low embodied energy of the mate-rial are of lesser importance.

Opinions on ETFE and PTFE foils

The second sub-section included questions aiming to understand both the level of knowledge of the particular respondent, and the attitude of the

Legend: 1.1 – Thermal performance and

insulation 1.2 – Sun and glare protection 1.3 – Daylight 1.4 – Provision of ventilation 1.5 – Durability 1.6 – Low material embodied energy1.7 – Recyclability

Energy-efficient façade properties

1.1 1.2 1.3 1.4 1.5 1.6 1.7

Of great importance

Of some importance

Of no importance

Do not know

100%90%80%70%60%50%40%30%20%10%0%

Perc

enta

ge o

f re

spondents

’opin

ions

14.1 Opinions on the importance of energy-effi cient facade material properties.

��



respondent towards using ETFE and PTFE as a facade material. The items that respondents were asked to rate for both ETFE infl ated foil cushions and PTFE-coated fi breglass fabric were:

• Aesthetic appeal• Insulation and thermal performance• Design versatility• Daylight transmittance• Shading• Ability to incorporate natural ventilation.

Results in Fig. 14.2 show a clear positive attitude towards the appearance of ETFE infl ated foil cushions, with more than 90% of architects saying that the material had ‘acceptable’ to ‘excellent’ aesthetic appeal and design versatility. Over half of the architects interviewed (58%) thought that ETFE-infl ated foil cushions had ‘acceptable’ insulation and thermal perfor-mance. However, only 16% regarded ETFE foil cushions as having ‘excel-lent’ thermal performance. This contrasts with the literature, in which ETFE typical triple-layered infl ated foil cushions have a low U-value of approxi-mately 1.9 W/m2K (refer to comparison matrix in Table 14.1).

The daylight transmittance of ETFE cushions was rated as ‘acceptable’ to ‘excellent’ by 75% of the interviewees. The manufacturer information confi rms that ETFE infl ated foil cushions can transmit up to 90% of the visible light spectrum (Vector Foiltec, 2009; Macleod, 2010).

A majority of architects (58%) said that ETFE infl ated foil cushions had ‘acceptable’ shading qualities. A quarter of them thought these prop-erties to be ‘poor’ with the reason that it is a translucent material and that they therefore did not regard it as being able to provide a building with a signifi cant amount of shading. This suggests that these architects were unfamiliar with the possibility of printing patterns on the foils to actively

Excellent

Acceptable

Poor

Do not know

Legend: 2.1 – Aesthetic appeal 2.2 – Insulation and thermal performance 2.3 – Design versatility 2.4 – Daylight 2.5 – Shading 2.6 – Ability to allow ventilation

ETFE façade materials properties

2.1 2.2 2.3 2.4 2.5 2.6

100%90%80%70%60%50%40%30%20%10%0%

Perc

enta

ge o

f re

spondents

’opin

ions

14.2 Opinions on typical ETFE infl ated foil cushions.

��



control solar gain and provide glare protection (see also Chapter 13, Section 13.4).

None of the architects thought that the ability to provide suffi cient ven-tilation in ETFE foil cushions was ‘excellent’, with a third admitting that they did not know how the material could easily incorporate a means of ventilation through openings.

Figure 14.3 indicates how architects rate the PTFE performance in regards to six facade material categories. Architects appear to be positive towards the aesthetic appeal and design versatility of PTFE (similar to ETFE) with all interviewees indicating an ‘acceptable’ to ‘excellent’ attitude.

Half of the interviewees said that PTFE had ‘poor’ insulation and thermal performance. Almost all of these architects said that this was due to the single skin and this performance would improve with the addition of another skin. This was an expected response as the comparison matrix (Table 14.1) shows a U-value of 4–5 W/m2K for PTFE.

The ideas on daylight transmittance of PTFE seem to be confl icting, with an almost equal distribution across the four possible responses. Only 8% were unsure of the shading properties of PTFE, with 67% rating the shading level of PTFE as ‘acceptable’ to ‘excellent’. Most architects seem to recog-nize PTFE as a material for temporary tents and shading structures.

Over half (58%) of the architects interviewed thought that the ability to incorporate ventilation was ‘acceptable’.

ETFE and PTFE facade material properties vs. double-glazed facades

The third and fi nal sub-section examined material properties. These ques-tions were asked to understand how architects thought ETFE and PTFE textile facades compare with a normal double-glazed unit with regard to these issues:

Legend:3.1 – Aesthetic appeal 3.2 – Insulation and thermal performance3.3 – Design versatility 3.4 – Daylight 3.5 – Shading 3.6 – Ability to allow ventilation

PTFE façade materials properties

3.1 3.2 3.3 3.4 3.5 3.6

Do not know

Poor

Excellent

Acceptable

100%90%80%70%60%50%40%30%20%10%0%

Perc

enta

ge o

f re

spondents

’opin

ions

14.3 Opinions on PTFE-coated fi breglass fabric (typical single-skin).

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• Life-cycle costs• U-value• Embodied energy• Recyclability• Cost.

The result of this comparison is shown in Fig. 14.4. It indicates that 58% of the architects interviewed did not know how the life-cycle costing of ETFE results would compare to glazing. This response may indicate that the interviewees could be unaware of the origin of ETFE being a Tefl on polymer material. The material in fact requires very little maintenance, as it is self-cleaning when it rains. Unlike a glazed facade that requires regular cleaning every 3 months, cleaning of the external surface of ETFE is recom-mended every 2–3 years.

A higher proportion of architects (42%) said that the U-value of ETFE was lower than double-glazing, compared with 16% who thought that it would be higher. This result means that most of the architects either assumed or understood the thermal performance of ETFE. With regard to the embodied energy, half of the architects interviewed thought ETFE had a lower energy content compared with glass. A third, however, did not know. This is a positive refl ection of manufacturers’ literature. Due to the low density of the material as well as the minimal energy used in its production, ETFE comes out on top in this regard.

The potential for reuse of ETFE was perceived as being lower compared with glass for 33% of the architects interviewed. In fact, all three materials are 100% recyclable.

In regards to costs, one-third of this group thought that ETFE would be more expensive than glass as a whole facade system, whilst 25% thought

Legend: 4.1 – Life-cycle costing 4.2 – U-value 4.3 – Embodied energy 4.4 – Recyclability/reuse potential4.5 – Cost

ETFE vs double glazing

4.1 4.2 4.3 4.4 4.5

More/higher

Same

Less/lower

Do not know

100%90%80%70%60%50%40%30%20%10%0%

Pe

rcenta

ge o

f re

spondents

’opin

ions

14.4 ETFE facade material properties vs. double-glazed facade.

��



that it could be a cheaper system. A quarter also did not know how the cost would be compared. Table 14.1 shows that ETFE is between A$600–800/m2 and a double glazed unit is between A$800–1000/m2 (design, supply and installation cost for a cladding system) (Macleod, 2010). Although the glass price in itself may be cheaper, the cost for the structure needs to be taken into consideration as well, to be able to compare it with an ETFE solution. Due to the light weight of ETFE, cost savings in the structure can occur and the system as a whole can be the more cost effective solution.

The overview of results for this comparison of PTFE with glass can be seen in Fig. 14.5. Architects were asked to rate how they thought PTFE performed in comparison to a typical double-glazed facade in the same fi ve facade material categories as mentioned above. Almost 60% of the architects interviewed admitted that they did not know how the life-cycle costing of PTFE-coated fi breglass fabric performed in comparison to glazing. Due to the Tefl on properties of the coated fabric, PTFE tends to minimize maintenance requirements throughout its lifespan. With a lifespan of approximately 20–30 years, PTFE would be likely to require replacement only once in a typical 50-year lifespan of a commercial building.

The architects were divided in their ideas on the U-value (thermal per-formance) of PTFE fabric. Nearly every second architect (42%) thought the U-value was higher (hence thermal performance was poorer than double glazing) and 42% thought the U-value was lower. According to Architen’s website, a typical single-layered PTFE fabric has a U-value of between 4 and 5 W/m2K and therefore performs poorer than a double-glazed facade system which has a U-value of approximately 3 W/m2K and lower (Architen Landrell, 2009; GJames Glass, 2009). The U-value of

Legend: 5.1 – Life-cycle costing 5.2 – U-value 5.3 – Embodied energy 5.4 – Recyclability/reuse potential5.5 – Cost

PTFE vs double glazing

5.1 5.2 5.3 5.4 5.5

More/higher

Same

Less/lower

Do not know

100%90%80%70%60%50%40%30%20%10%0%

Perc

enta

ge o

f re

spondents

’opin

ions

14.5 PTFE facade material properties vs. double-glazed facade.

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PTFE can improve with the addition of a second layer and perform similar to a double-glazed unit for horizontal application.

Also, every second architect (42%) thought that the embodied energy of PTFE was lower than that of glass compared with 33% who thought it would be higher; the other third did not know. The literature tended to emphasize that the embodied energy of PTFE fabric was lower than that of traditional materials such as glass. This, of course, is explained by the low energy used in the production, transport and installation of the light-weight material. Savings in energy would be achieved by using smaller delivery trucks to get the material to site and the resultant smaller equip-ment required in its installation.

With regard to the recyclability and reuse potential of PTFE in compari-son to glass, every second interviewee perceived it to be much the same. Manufacturers have noted the ease of recyclability of all these materials that can all equally be returned back to their virgin state and recycled into new products.

Half of the architects interviewed thought that the cost of PTFE in comparison to a double-glazed facade would be lower, whilst only 16% believed it would be more expensive. Although the base cost of glazing is lower than that of PTFE, this does not include the structure that would be required to support the glazed system. The reduced quantity of structure required to support lightweight PTFE would result in cost savings. This appears to be refl ected in the responses.

14.3.3 Opinions of architects on the integration of textiles into energy-effi cient buildings

In Part C of the interview, open-ended discussion questions were asked in order to discover the opinions and attitudes of architects with regard to the success of textiles (ETFE and PTFE) in satisfying the performance require-ments of a material to be incorporated into an energy-effi cient building. The two research questions investigated here are:

• What are the potential obstacles to greater textile use in Australia?• What incentives would be required to encourage their future use in

energy-effi cient facades?

Table 14.3 provides an overview of the questions and answers.The majority of the architects interviewed (67%) thought that textiles

were a successful building material for integration into an energy-effi cient building. A third of the architects mentioned that the main reason why textiles were unsuccessful in satisfying the performance requirements was due to the need for highly technical expertise to maintain and install these

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Table 14.3 Architects’ opinions on application possibilities of textile facades in Australia



Question 1a – Textiles as a successful facade material for an energy-effi cient

building

Category 1: Successful facade material for energy-effi cient building

67% ETFE more successful than PTFE in performance; both successful if used in correct application

Category 2: Unsuccessful as a facade material for energy-effi cient buildings

33% Textile systems require a high level of technical expertise

Question 1b – Application of textiles

Category 1: Most suitable application for ETFE

25% Sporting arenas

Category 2: Most suitable application for PTFE

25% Sporting arenas

Category 3: Most unsuitable application for ETFE

17% Domestic; too expensive

Category 4: Most unsuitable application for PTFE

17% Offi ce buildings, because signifi cant amount of thermal insulation required

Question 2 – Attitude towards wider application in Australian buildings

Category 1: Positive about textiles being more commonly used

50% Australia needs to be encouraged to bring more contemporary materials to the landscape

Category 2: Negative about textiles

17% Not aesthetically pleasing to designer due to distortion

Category 3: Both positive and negative

33%

Question 3 – Obstacles to the use of textiles in Australia compared to

overseas

Category 1: Client 42% Unwilling to accept change; wary of new products

Category 2: Australian conservative culture/perception

42% Public acceptance of something different

Category 3: Aesthetics 17% Distortion not visually pleasing; do not like milky appearance

Category 4: Design limitations 42% Not suitable for all projectsCategory 5: Risk and warranty 25% Not manufactured locally;

imported products carry higher risk

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Table 14.3 Continued



Category 6: Material properties

50% Looks dirty; not enough knowledge about maintenance, durability, structural integrity; insecurity towards resistance to vandalism; not robust looking

Category 7: Industry lack of knowledge

50% Designers and builders do not understand c.f. overseas, low understanding of LCC

Category 8: Australian conditions

8% Harsh Australian climate

Category 9: Cost 67% Perception of cost unknown, assume expensive because exclusive and requires specialist contractor, not enough manufacturers to give competitive price

Question 4 – How designers can be encouraged to apply textiles to

improve the performance of façades in Australia

Category 1: Increase education

58% Increase status, credibility and knowledge of textiles; more information needs to be available

Category 2: Proven statistics 25% Proven case studies of building in operation should be made more readily available

Category 3: Improved aesthetic appearance

50% Better detailing and translucency

Category 4: Reduce cost 17% Make better value for moneyCategory 5: Public acceptance 25% Overcome conservatismCategory 6: Combine with

traditional materials8% Solutions to address glass for

vision panels – manufacturer driven

Category 7: Increased no. suppliers

8% Allow better market competition

Question 5 – Future potential opportunities for textiles

Category 1: Use more in existing applications

58% Public/iconic buildings; needs to be a project important enough for acceptance

Category 2: Domestic 17%Category 3: Schools 17% For interactive learningCategory 4: Combination with

traditional materials17% e.g. glass

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non-traditional materials. A number of architects also commented that both ETFE and PTFE envelopes could be successful for integration into an energy-effi cient building, if used appropriately.

Every fourth architect suggested that both ETFE and PTFE were best suited to be applied to a sporting arena, because of the large spans able to be achieved and the dynamic appearance. The most unsuitable application for ETFE infl ated foil cushions appeared to be domestic housing and offi ce buildings for PTFE fabric.

Half of the architects interviewed had a positive attitude when asked how they would feel if textile facades were becoming more popular in Australian architecture. If used in a suitable application, most liked the idea of seeing the built environment using more contemporary building materials and breaking free from traditional components. A minority (17%) of the interviewees were negative about the wider application of textile facades in Australia with regard to the aesthetic appearance of ETFE. Unattractive repairs of an ETFE canopy on a project in Melbourne were raised by several architects and must have led to the assumption that there are not enough examples of the material in operation that are maintained and repaired well to provide Australian designers with confi -dence in the use of the material. Many overseas projects have successfully proven the ability to maintain the aesthetic qualities of ETFE. The per-ception of the cost of textile materials was a major obstacle according to 67% of the architects interviewed. Many of the architects assumed that these materials would be more expensive than traditional facade materials due to the exclusivity of textiles and limited manufacturers for competi-tive pricing.

Other major obstacles to the wider use of textile facades in Australia included a lack of knowledge with regard to life-cycle costing, maintenance requirements, durability, structural integrity, and resistance to vandalism, as well as client and Australian cultural conservatism – a ‘why change?’ attitude. Some also seemed to feel that there were design limitations, because they appeared to be insecure about the correct application and detailing.

Over half (58%) of the architects felt that an increase in education about textiles for use in facades would encourage architects to look to textiles as a solution for a high-performance facade in an energy-effi cient building. This would increase the status and credibility of these materials for envi-ronmentally sustainable architecture. Designers would also be encouraged if textiles could be combined effectively with glass to increase the number of building applications.

Again, over half (58%) of the interviewees said that textile facades in energy-effi cient buildings had the greatest opportunity to be applied to

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buildings similar to those overseas, such as public, and iconic or high-profi le projects.

14.4 Summary of results

The majority of the architects interviewed had between 10 and 20 years of experience in the design and construction industry and a high level of expe-rience in energy-effi cient building and facade design. More than half had a low level of knowledge of textiles, such as ETFE infl ated foil cushions and PTFE-coated fi breglass fabric. Within this group, 75% had never consid-ered using textiles for a project even though over 60% of the architects had heard about textiles in buildings between 5 and 10 years ago. However, 58% had only heard about textiles as permanent facade systems between 1 and 5 years ago, the majority noting that this was through the recognition of high-profi le projects such as the Burj Al Arab Hotel (PTFE) in Dubai, United Arab Emirates, Allianz Arena (ETFE) in Munich, Germany and the National Aquatic Centre (ETFE) in Beijing, China.

All architects regarded thermal performance, sun and glare protection, daylight, provision of ventilation, durability, low material embodied energy and recyclability as critical facade material properties for the performance of an energy-effi cient building.

Whilst both ETFE and PTFE were well received with regard to aesthetic appeal and design versatility, knowledge of ETFE appeared to be more consistent amongst the interviewees, predominately in relation to thermal performance. Life-cycle costing was identifi ed as a consistent gap in the knowledge of the interviewees, with 60% admitting that they did not know how ETFE and PTFE life-cycle costs compared with those of a glazed facade. It is assumed, therefore, that the low maintenance and high durabil-ity of these fl uoropolymer textiles is not well known in the industry. Both materials are polymers of Tefl on and therefore have non-stick and self-cleaning properties with a life-span between approximately 30 and 40 years for PTFE and ETFE respectively. This information is therefore related to minimal replacement and reduced maintenance costs over the lifetime of the material as facade cladding.

The cost of textiles was also identifi ed as a common gap in knowledge, with 25% not knowing how it compared to glazing. It has been recog-nized that due to the light weight of textiles as a facade material, the reduction of structural framework required compared with the structure needed to support glazing could result in signifi cant cost savings. The system as a whole needs to be considered in order to make an accurate comparison. Lack of information with regard to cost and maintenance have been found to be a major downfall in the misinterpreted cost assess-ment of textiles.

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A majority (67%) of the architects interviewed thought that textiles were a successful material for integration into an energy-effi cient building, par-ticularly if used in the right application; 33% thought that it was unsuccess-ful because of the highly technical expertise required to install and maintain a non-traditional facade material.

Half of the interviewees were positive about the prospect of textile facades becoming more popular, again if used in the correct application. These architects felt that it would be a positive result to see more contem-porary materials becoming a part of the Australian built environment. The interviewees who were negative about the wider application of textile facades felt that the reason was the lack of good aesthetic examples in Australia, especially with ETFE. There are not enough examples of the material in operation that are maintained and repaired well to provide Australian designers with confi dence that the material can be aesthetically pleasing compared with the many overseas projects which have successfully proven the maintenance of aesthetic qualities of ETFE.

Obstacles to the wider use of textile facades were identifi ed as cost (67%) due to the exclusivity and limited manufacturers to provide a competitive price; and a lack of knowledge regarding life-cycle costs, maintenance, durability, detailing and correct application of both textiles.

14.5 Conclusions and deliberations on

future developments

The literature review revealed the importance of high-performance facades in energy-effi cient buildings and the contribution that ETFE and PTFE can make. In summary, textiles may provide an excellent alternative to tradi-tional glazed facades by encouraging passive design due to good daylight transmission, thermal insulation and low maintenance benefi ts. It has become clear that textile facades should be considered more frequently in the design of an energy-effi cient building.

This research also showed that there were barriers in Australia to the adoption of textiles as a facade material and that leading architects have some awareness of their energy-effi ciency benefi ts. This encouraging support for implementing textiles as a more contemporary building mate-rial does augur well for the more widespread adoption of textiles, once some of the barriers identifi ed here can be overcome.

To provide architects with increased ability to plan the use of textiles in the future, cost analyses need to compare textile solutions with glass alter-natives, taking into account the supporting structure and framing systems, the constant energy consumption of the pumps for ETFE cushions and the durability of the system as a whole, as well as cleaning issues to consider the self-cleaning effect of some textile materials. As the cost-related issues

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are extremely important for the decision-making process in the industry, this fi eld is currently one of the research areas of the lead author at The Univeristy of Melbourne.

To encourage future use of textile materials in facades, architects have suggested increased education in this area to promote correct detailing and application, and to endorse the materials’ benefi cial properties and their contribution to energy-effi cient design. The incorporation of textiles with traditional materials as a standard system might further expand the suit-ability to a wider range of building facades.

The built environment has an enormous impact on greenhouse gas emis-sions. Effort to reduce these emissions raise the importance of minimizing the operational energy of new buildings, but most importantly the existing building stock too. The existence of these materials and their usefulness in reducing the operational energy consumption of a building provide archi-tects with new tools on the way to a more sustainable architecture pursuing the mitigation of climate change.

14.6 References

Architen Landrell (2009), www.architen.com (accessed 2.9.2009)Armijos, S (2008), Fabric Architecture: Creative Resources for Shade, Signage, and

Shelter, Norton, New YorkCole, R, Kernan, P (1996), ‘Life-cycle energy use in offi ce buildings’, Building and

Environment, Vol. 31, No. 4, pp. 307–317Dimoudi, A, Tompa, C (2008), ‘Energy and environmental indicators related to

construction of offi ce buildings’, Resources, Conservation and Recycling, Vol. 53, No. 1, pp. 86–95

Fabric Architecture (2008), ‘Sustainable Fabric Basics’, Sourcebook Sustainable Design Techniques, Fabric Architecture, 7/8-2008, Vol. 20, No. 4

GJames Glass, www.gjames.com.au (accessed 16.9.2009)Harvey, D (2009), ‘Reducing energy use in the building sector: measures, costs and

examples’, Energy Effi ciency, Vol. 2, pp. 139–163Hightex (2009), www.hightexworld.com (accessed 2.9.2009)LeCuyer, A (2008), ETFE – Technology and Design, Birkhäuser Verlag AG,

Switzerland, pp. 32–148Macleod, A (2010), Vector Foiltec Australia, personal communicationOECD (2003), Environmentally Sustainable Buildings – Challenges and Policies,

OECD Publications Service, Paris, pp. 20–24Rawlinsons (2009), Rawlinsons Australian Construction Handbook, Rawlinsons

Publishing, AustraliaRobinson-Gayle, S, Kolokotroni, M, Cripps, A, Tanno, S (2001), ‘ETFE foil cush-

ions in roofs and atria’, Construction and Building Materials, Elsevier, pp. 323–327

Shields, T (2002), ‘Performance of a single glazing assembly exposed to a fi re in the centre of an enclosure’, Fire and Materials, Vol. 26, pp. 51–75

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Simmonds, T (2006), ‘Woven surface and form’, Architextiles/Architectural Design, 11/12-2006, Vol. 76, No. 6, pp. 82–89

Stokes, N (1998), The Glass and Glazing Handbook, Standards Australia, Australia, pp. 33–56

Tanno, S (1997), ‘Foiled again’, RIBA Journal, Vol. 104, No. 7, pp. 86–87Thormark, C (2006), ‘The effect of material choice on the total energy need and

recycling potential of a building’, Building and Environment, Vol. 41, pp. 1019–1026

Vector Foiltec (2009), ‘Technical information’, www.foiltec.com (accessed 3.5.2009)Wright, B (2009), ‘Modeling night light’, Fabric Architecture, 3/4-2009, Vol. 21, No. 2

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420

15Innovative composite-fi bre components

in architecture

G. POHL, Saarland University of Applied Sciences, Germany and M. PFALZ, FIBER-TECH Products

GmbH, Germany

Abstract: This chapter presents basic information on the most important materials and production technologies used for fi bre-reinforced polymer (FRP) composites for buildings. Starting with an overview of common materials and introducing the background, the specifi c focus is then on ‘how to start with and how to make’. Therefore, three sections show as examples the ‘make of’ projects – ‘Space Offi ce’ by Fritz Gampe, ‘The Walbrook’ by Foster and Partners, and ‘Feathered Wing’, a fl oating roof by Julia and Göran Pohl – each at a certain stage of fi nalisation.

Key words: fi bre reinforced composites in architecture, FRP architecture, composites for buildings, lightweight architecture, lightweight constructions, lightweight institute, Space Offi ce, The Walbrook, Feathered Wing, theatre festival Feuchtwangen, convertible roof, GFK Architektur, transportable architecture, biomimetics architecture, stage design.

15.1 Introduction

Plastic materials are based on polymer chains with organic groups on a synthetic or semi-synthetic base. Numerous additives and methods of fab-rication, treatment and assembly make these materials suitable for a wide range of technical needs. As a result, in the course of the last century, polymer-based materials such as plastics have become essential compo-nents in our lives. The versatility of plastics, for example, can be seen in buildings. PVC pipes and cable insulation materials were among the fi rst uses of plastics for houses. Nowadays, fl oor coatings, facade elements, insulation foams, door and windows frames, laminates and all sorts of architectural profi le components are used together with interior accessories and furniture made of plastic.

One of the most important characteristics of polymer materials is that they are lightweight. The term lightweight construction is often used in connection with so-called ‘lightweight construction materials’ such as fi bre-reinforced polymer composites. These are important because of their high strength at relatively low density. However, conventional construc-

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Innovative composite-fi bre components in architecture 421


tion is not necessarily lightweight construction simply because traditional materials have been exchanged with lightweight materials. Lightweight construction implies construction methods that take full account of mate-rials such as fi bre-reinforced polymer composites. There is no ‘optimal’ lightweight material, but rather a broad selection of materials that can be useful in lightweight construction.

An optimised lightweight construction is always a combination of concept, environment, materials and design. Structurally optimised lightweight con-struction is related to the arrangement of structural mass in a way that the forces acting upon the construction are optimally absorbed and transferred. The structure can be seen as the connection between the individual func-tional elements and the total construction, with the job of absorbing and transferring all the forces affecting the structure so that it remains stable. A structure can be considered under maximum duress when, under the greatest amount of possible force acting upon the total structure, each individual material element is brought to the limit of its load-bearing capac-ity. Optimal stress can also be considered as a situation where the material withstands all the forces applied to it in varying environmental conditions well within the materials’ and components’ limits of tolerance. This is achieved through appropriate design.

Fibre-reinforced polymer (FRP) composites have had a particular impact in architecture because of their low weight, load-bearing capacity and ver-satility. Since the quantity and distribution of the fi bres in the matrix of FRP composites can be tailored for a specifi c end use, FRP composites are ideal materials for structurally optimised lightweight construction. This chapter reviews the most important materials and production technologies used in fi bre-reinforced composites for buildings. The focus is practical, looking at three case studies which explore different projects, each at a different stage of development, as examples of how to use these materials effectively in buildings.

15.2 Historical background

The involvement of plastics in building design began with furniture in the 1950s. Famous names include Eero Aarino, Verner Panton, Ray and Charles Eames and Arne Jacobsen. The list should include fi gures such as Peter Ghyczy who designed the famous ‘Egg’ garden chair which rivalled the fi breglass ‘Bubble’ chair by Eero Aarino, as well as the innovative offi ce furniture designed by Maurice Calka. Verner Panton’s chair, designed in 1960 and produced from 1967, was perhaps the fi rst single-unit injection-moulded chair, made of fi breglass and polyester.

The Space Age of the 1960s and 1970s, beginning with the launch of Sputnik I by the Soviet Union in the 1950s, had a tremendous impact in

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many areas, including art, design and architecture. One of the major events where ‘space-age’ architecture was promoted was the 1970 World Exhibition in Osaka. Inspired by architects like Peter Cook and Ron Herron of Archigram, the exhibition symbolised the vision of self-suffi cient utopian communities both on Earth and in space, built from new materials such as FRP composites. Drawing from the work of organisations such as the National Aeronautics and Space Administration (NASA) in the USA, and the ‘Space House’ and ‘Space Offi ce’ concepts developed by the European Space Administration (ESA), designers such as Frei Otto, Kento Tange, Ted Happold and others experimented, for example, with the idea of self-contained communities consisting of separate, modular, shell-like living units. This concept was used, for example, for buildings in the Antarctic in the 1970s.

At the same time, Günther Behnisch’s polycarbonate roofi ng for build-ings at the Munich Olympics in 1972 helped to set the standard for a new lightweight, elegant construction style that would continue to be refi ned over the following decades. The potential benefi ts of this new architectural style can also be seen in the ‘Tournesol’ series of swimming pools in France, designed in 1972 by Bernhard Schoeller, typically with a span width of 34 m and a 1020 m2 surface area. The ‘Tournesols’ were planned to combine the benefi ts of an enclosed bath with those of an open-air bathing experience (Fig. 15.1). In the winter the hall is closed and used as an enclosed swim-ming pool, whereas in summer the hall is opened. The construction is composed of lightweight individual shells on an arched steel frame which can be moved to open the pool to the outside air. The shells are constructed from glass fi bre with a 40 mm phenol foam core in a sandwich structure. Light passes through polycarbonate skylights to illuminate the hall when the shell is closed.

Between 1972 and 1984 a total of 180 ‘Tournesols’ were built. The main problems with these structures resulted from the lack of suffi cient insula-tion in the shells and the failure of the rubber seals between the individual shell elements. This refl ected early problems in understanding the longer-

15.1 Tournesol in Obernai, France.

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term performance of the new materials used and the resulting failures in manufacture, coating, design, construction and maintenance. The innovative petrol station design by Matti Suuronen near Lempäälä in Finland is a notorious example of this failure to fully understand the materials used and their capabilities (Fig. 15.2). Buildings using modern FRP composite materials have now largely overcome these early problems, partly by learning from these pioneering examples and partly by using the advances in materials and surface protection techniques developed in marine, aerospace and automobile engineering. These industries have also greatly advanced composite properties such as strength, stability and fi re retardancy.

15.3 Materials for composites

A fi bre-reinforced composite material is manufactured through conglom-eration: fi bres of unusually high strength are embedded in a viscous matrix which, when hardened, anchors the fi bres in the matrix, creating the com-posite material. Should two or more types of fi bre be used in the composite, the composite is considered a hybrid composite. The role of the matrix is to fi x the fi bres in position and optimally transfer the forces working on the material to the fi bres. This requires excellent adhesion of the resin to the fi bres. The matrix also determines the surface quality, resistance to ageing, chemical resistance, electrical and other qualities of the composite material. The mechanical qualities of the composite, such as load-bearing, tension and bending capacity, or impact resistance, are primarily determined by the type and amount of fi bre used, and the method of application which infl u-ences the distribution and orientation of the fi bres. All of these can be tailored to produce a composite that meets the particular requirements of the component used in the building design. Figure 15.3 shows the produc-tion process.

15.2 Petrol station by Matti Suuronen near Lempäälä, Finland.

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15.3.1 Matrix materials

Table 15.1 gives an overview of various matrix materials. There are basi-cally two types: thermoplastic and thermoset or duroplastic (Fig. 15.4). Although thermoplastic matrix materials have defi nite benefi ts over duro-plastics, their application is not widespread and they are not discussed here. Once they have hardened, duroplastics can no longer be melted, and, in the case of epoxy resin, achieve a very high degree of strength and stiffness while possessing a very low tendency to shrinkage.

The most widely used resins are unsaturated polyester (PU) resins. The hardening process occurs as a radical polymerisation and the result is only

Basic materials

Fibres (e.g. aramid,glass, carbon)

Resin (e.g.polyester,epoxy,vinyl ester)

Bidirectionallaminateresilient inseveral directions

Unidirectionallaminatehighly loadable infibre direction

Laminate(single layer)

Pressing,hardening(several layers)

Composite

15.3 Production process of FRP.

Table 15.1 Overview of various matrix materials

Characteristics of unreinforced resins

Unit Epoxy resin Polyurethane resin Vinyl ester resin

Resin LF Hardener LF 3

U 569 TV-01V Palatal A 430-01

Density g/cm3 1.18–1.20 1.19 1.067Bending strength MPa 110 130 150Tensile strength MPa 70 80 90Ultimate strain % >5 3 8.4Impact strength kJ/m2 45 40E-modulus

(bending test)GPa 3.0 3.9 4.0

Glass transition temperature

°C 90–95* 130 130

* 10 h post-curing at 80°C.

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secondarily infl uenced by mixing errors. Once the hardening component is introduced, the process of hardening begins. PU resins are often applied as fi llers. One positive aspect of the usage of PU resins is their relatively low cost. Negative aspects of PU resins are lower mechanical stability and higher shrinkage as compared to epoxy resins.

A very high degree of integration of matrix and fi bres can be achieved with epoxy resins. In addition, they have good thermal stability and very low shrinkage. However, it is absolutely essential that the correct mixture of resin and hardener is achieved. A disadvantage of epoxy resins is the relative high material cost when compared to PU resins.

Phenol resins occur through the condensation of phenols with formal-dehyde. A side-product is water, which can lead to porosity of the laminate. One benefi t of phenol resins is their ability to withstand high temperatures. A disadvantage is their corrosive nature. Phenol resins are often used in industrial applications where their corrosive nature is not a problem.

It is not the main focus of this book to describe the use of wood–polymer composite materials for buildings. They are used primarily to replace tra-ditional timbers in components such as decking, though they have more occasionally been used in structural applications. Artec, a furniture design company based in Finland, has, for example, used L-shaped components made from these composite materials to construct a very lightweight show-room, designed by the architect Shigeru Ban (Fig. 15.5).

15.3.2 Reinforcing fi bres

In polymer–fi bre composites, it is generally the reinforcing fi bres that deter-mine the strength of the material. The strength of the fi bres is much higher than that of the matrix material. The tearing strength of artifi cial fi bres, for example, is generally higher than that of metallic materials. As a result, polymer-based ropes can actually withstand greater forces than steel ropes. Although strong, the density of the most common fi bres is lower than that

(a) (b)

15.4 (a) Thermoplastic integration; (b) duroplastic integration.

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of aluminium, which points to a great potential for lightweight construction. Figure 15.6 shows the relationship between tension and elasticity for the most common reinforcing fi bres.

Glass, aramid and carbon fi bres are the most commonly applied fi bres in polymer–matrix composites. Further fi bres composed of boron or basalt

CarbonUHM

CarbonT3.6

Tensile

str

ength

(M

Pa)

CarbonT 7.0

Aramid(Kevlar 49)

E-Glass

Fracture strain (%)

0 0.5 1 2 3 41.5 2.5 3.5

7000

6000

5000

4000

3000

2000

1000

0

R-, S-Glass

HPPE(Dynema SK 60)

15.5 Artec Exhibition room in Helsinki, Finland.

15.6 Tension–elasticity relationship for the most common reinforcing fi bres.

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have found limited use to date. The various fi bres can be differentiated by their mechanical qualities and methods of application to the matrix.

Glass fi bres are the most commonly used reinforcing fi bres in polymer composites. They have good mechanical, chemical and dielectric qualities, and are relatively inexpensive. Fibreglass can be delivered in various shapes as e-fi bres, r-fi bres and s-fi bres. Because it is the most inexpensive, e-fi breglass (Table 15.2) is the most commonly used, even though it displays less stiffness and strength than r-fi bres and s-fi bres. In order to improve the adhesion between fi bres and matrix, an adhesion agent is introduced. The adhesion agent helps the matrix to fl ow around the fi bres so that they are optimally embedded. Different adhesion agents can impart different levels of strength to a composite.

Aromatic polyamides or aramids such as Kevlar® and Twaron® were developed at the beginning of the 1970s. Aramid fi bres can be divided into low modulus and high modulus types. Of the three specifi ed fi bre types treated in this chapter, aramid fi bres have the lowest specifi c weight and are characterised by extreme resilience. They can produce laminates that display practically no temperature distortion across a range of tempera-tures. However, their resilience makes aramid fi bres diffi cult to use. Fabrics made with these fi bres can only be cut with special micro-toothed shears or with water-jet cutting processes. Aramid fi bres are UV-sensitive and display a tendency to absorb water. The adhesion of fi bres with conven-tional matrix materials is not as high as with fi nished fi breglass or carbon

Table 15.2 Important characteristics of e-fi breglass as well as their typical composition

Characteristic Unit E-glass

Density g/cm3 (20°C) 2.6Tensile strength MPa 3400E-modulus GPa 73Ultimate strain % 3.5–4Poisson ratio – 0.18Resistivity ohm/cm (20°C) 1015

Dielectric constant 106 Hz 5.8– 6.7Thermal expansion coeffi cient 10−6/K 5

Chemical compositionSiO2 % 53–55Al2O3 % 14–15B2O3 % 6–8CaO % 17–22MgO % <5K2O, Na2O % <1Other oxides % ca. 1

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fi bres. Aramid fi bres tend to be used in those situations which require excel-lent resilience (such as abrasion resistance) and particularly low weight. Typical applications include bullet-proof vests and sports canoes and kayaks.

Carbon fi bres are composed of more than 90% pure carbon. They have been industrially produced since the middle of the 1970s. The adhesion of carbon fi bres in epoxy resins is very good, creating a particularly strong composite. An improved integration of fi bres in the matrix can be achieved with various fi bre surface treatments. Because of their high modulus, carbon fi bres are suitable for applications where a high degree of stiffness is neces-sary. Carbon fi bres, as opposed to fi breglass and aramid fi bres, are also able to conduct electricity.

A carbon fi bre proper is a very thin thread of carbon atoms, bonded together in microscopic crystals some few microns (thousandths of a mil-limetre) in diameter. The better the alignment and the purer the carbon, the stronger is the material. Pretensioning during production and the tem-peratures of carbonisation and subsequent graphitisation have a decisive infl uence on the purity and orientation of the graphite layers in the fi bre. At a range of some nanometres resolution, the carbon thread looks like wood bark with a very large surface area. As an example, an assumed fi bre diameter of 7 microns and a fi bre fraction of 50% yields a theoretical surface of 2800 cm2 for every 1 cm3 of laminate. Thousands of very thin threads are twisted together to form a yarn. The number of threads used to form a yarn gives the thickness of the yarn, expressed as 1 k (1000) to 3 k for very fi ne yarns and up to 48 k for very thick yarns. For some applica-tions yarns of 80 k or even 320 k and beyond are produced.

There are a range of fi bre types available, which cover a broad spec-trum of material stiffness and strength. The most widely used and inex-pensive carbon fi bres (Table 15.3) are high tenacity (HT) fi bres. A good

Table 15.3 Qualities of carbon fi bre types

Characteristic Unit HT (HTA) IM (IM600) HM (HM35)

Density g/cm3 (20°C) 1.78 1.8 1.97Tensile strength MPa 3400 5400 2350E-modulus GPa 235 290 358Ultimate strain % 1.4 1.7 0.6Resistivity ohm/cm (20°C) 710 – 710Thermal expansion

coeffi cient10−6/K −0.1 – −0.5

Thermal conductivity

W/mK 17 – 115

Specifi c heat J/kgK 710 – 710

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compromise can be found in the use of intermediate modulus (IM) fi bres. They have a higher degree of stiffness and strength than HT fi bres, but are less expensive than the high-modulus (HM) fi bres. High-modulus (HM) and ultra-high-modulus (UHM) fi bres are created at higher tem-peratures than the other types of carbon fi bres and are not only the best performing in terms of strength but also the most expensive.

More recently basalt fi bres have gained in popularity. The basic material is natural basalt stone (with a composition of at least 50% SiO2) which is then treated using a pyrolytic process (similar to the carbon fi bre). The main challenge during the production process is to eliminate the high quan-tities of iron impurities (FeO or Fe2O3) in the basalt mineral. Basalt fi bres can be used in all types of resins (epoxy, phenol, polyester).

Natural fi bres are harvested or produced more or less directly from natural bio-products. Flax, coconut and hemp fi bres are the most widely used fi bres. As these materials have limited strength and other weaknesses (e.g. a tendency to decay organically), they are not widely used in the build-ing sector. A famous example of their use in the car industry was the ‘Trabant’ car manufactured in the former German Democratic Republic which used cotton-reinforced fi bres for the exterior skin.

15.3.3 Core materials for sandwich construction

A so-called sandwich or laminar composite consists of external layers (e.g. of FRP composites) and a core material that is glued to or injected between these layers so that it adheres to them. Shell elements with large surface areas are possible with the sandwich construction technique, providing load-bearing capacity is low. The core material is generally much thicker than the covering layers. During bending the thinner shell layer experiences an almost normal moment, whereas the supporting layer within experiences compression and expansion moments. Of decisive importance in the sand-wich construction is the compression and expansion stability of the core material as well as suffi cient adhesion between the internal core material and the covering layers.

Core material in a honeycomb structure (Fig. 15.7) balances stiffness and weight and can be applied in very large shell elements. Honeycomb is usually made from aluminium or paper sheets, though polyamide is also used. The adhesion of paper-based honeycombs to fi bre-composite shells is good. Aluminium honeycombs are less expensive than polyamide honey-combs and are able to absorb a great amount of energy in case of impact. Polyamide honeycombs are composed of aramid paper steeped in phenol resin. Polyamide honeycombs are characterised by low weight, high com-pression strength and fi re resistance in comparison with all other core materials for sandwich construction.

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Because of its low specifi c weight, balsa wood (ca. 140 kg/m3) is often used as a core material. Extruded foams with a density between 30 and 110 kg/m3 are also often used as internal core materials (Fig. 15.8), particu-larly as they have good insulation and soundproofi ng qualities. It is also possible to manufacture foam plates for use as core materials. However, adhesion to the covering layers is problematic.

15.3.4 Fire-retardant composite materials

The common matrix materials in FRP composites are fl ammable. However, FRP composites in buildings must meet the relevant fi re regulations. The requirement of FRP composite components to be fi re-resistant can generally be met by applying a gel coat, by putting appropriate additives in the matrix, or through the inclusion of fi re-retardant core materials

15.7 Core material as a honeycomb sandwich.

15.8 Core material as a foam sandwich.

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in a sandwich composite structure. Often a combination of these techniques is used. Tests on the fi re-retardant properties of composite materials can be carried out in a combustion chamber by certifi ed examining institutions.

The application of a gel coat creates an ‘active’ coating: in a fi re, the gel swells and foams, thereby protecting the underlying material. Fire-retardant additives can also be brushed or sprayed on to the surface to be protected in dimensions of between 0.8 and 1.3 mm. Polyester resin is often used for this purpose, as its viscosity is low enough to allow the addition of a higher volume of fi re-retardant particles. On the other hand, these solid particles can lower the mechanical strength of the resin system. As a result, applica-tion of these additives is often restricted to roofi ng components. Their usefulness in structural components is limited. As an alternative, phenol can be added to the resin itself. In fi re-resistant sandwich constructions, both Nomex® and Airex® honeycomb core provide high-quality fi re-protection. PVC or PET foam can also be used. Figure 15.9 shows the construction of a gel coat with fi ller.

There are also toughened, hybrid epoxy/glass prepregs now on the market with low fl ammability and heat-release properties originally designed for producing high-performance composite parts for modern air-craft interiors. These prepregs offer superior strength and other qualities when compared to traditional phenolic systems. The prepregs are suitable as a skin for honeycomb structures, for example.

15.4 Design and manufacture of composites

for buildings

A typical composite is made up of multiple individual layers, usually of fi bres in differing directions. In most cases, the forces are transferred through the matrix into the fi bres within the layers. Since the matrix is the weaker of the two components, it is of utmost importance to plan the points at which the forces are transferred to the fi bres. Dimensioning means

Five layers EP prepreg(s = 2.5 mm)

Six layers EP prepreg(s = 3 mm)

Filler

Bonding primer

EP-gel coat SG1/SH2(s = 0.8–1.3 mm)

Core material foam or balsawood (s = 20–30 mm)

15.9 Gel coat plus fi ller (according to: WELA Flammstop).

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selecting the appropriate materials and their optimal relationship to each other. The goal of dimensioning with fi bre-reinforced materials is the cal-culation of the required fi bre lengths and their orientation in the matrix. Finite element modelling can be used to simulate composite composition and likely performance. However, since the qualities of FRP laminates are dependent to a great degree on specifi c production-related variables, these theoretical calculations can only serve as a starting point. It is usually nec-essary to conduct experimental trials with sample composite materials. This is because there are very few reliable material values at hand. On the basis of these trials, laminate protocols and cutting plans are created for the production phase.

As has been noted, the properties of composite materials can vary enor-mously, depending on the constituent materials and the ways they are combined during processing. Different processing techniques have differ-ent effects on the material and fi nal component. The following sections look at different processes and their effect on the characteristics of composite building components.

15.4.1 Hand laminating process

Laminating by hand is the simplest way of producing fi bre composite build-ing components. The fi brous material in the form of rovings, mats or fabrics is usually laid on the mould and soaked with the matrix resin using brushes or rollers. This is almost exclusively undertaken with thermoset or duro-plastic polymers as the matrix material because their low viscosity enables an even degree of integration with the fi bres. The layering of the fi bres and the integration of the fi bres with the matrix material takes place simultane-ously with the formation of the component shape. After the fi nal hardening of the matrix, the component can be removed from its mould and fi nished with appropriate tools.

Hand laminating (Figs 15.10 and 15.11) requires only a minimum of fi nancial investment in equipment and enables the creation of highly complex component geometries as well as the inclusion of various fi bre materials in a single object. A fi bre content of up to 40% can be achieved, which can be increased further with a subsequent pressure treatment during hardening. Disadvantages of the process are that it is slow, labour-intensive and therefore relatively expensive to operate.

15.4.2 Prepreg process

It is possible to improve the distribution of fi bres in the matrix material when the fi bres or fi bre sheets are mechanically pre-impregnated with the matrix. Such pre-impregnated material is classifi ed as prepreg. In this

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Resin application

FabricSaturated fabric

Separationlayer

Cavity

Colouredlacquer

15.10 Hand laminating process.

15.11 Hand laminating process.

process, the fabric or rovings are mechanically coated with the matrix and rolled up with a protective foil (Fig. 15.12). In order for it to function, only premixed matrix can be applied. With systems that only harden at high temperatures, it is possible to use prepreg fi bres stored for up to 12 months. Heat-hardening prepregs generally require a heat treatment exceeding 120°C and a pressure of 1 bar to compress the laminate during the harden-ing process. Heat-hardening prepregs prepared using the so-called auto-clave technique achieve the highest quality but are also very expensive.

A cheaper alternative is the cold temperature hardening prepreg system. As opposed to heat-hardening prepregs, where the prepreg fabrication can take place at a different place and time than the manufacture of the ulti-mate component, in the cold temperature process the fabric or rovings are coated with the matrix at the point where the component itself is made.

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The same air-drying laminating resins can be used as a matrix material as are used in hand laminating. These prepregs must be immediately used after their fabrication, and are generally cut and hand-placed in the moulds.

15.4.3 Spinning technology

In spinning technology (Fig. 15.13), the fi bres are rotationally spun around a more or less symmetric core. The technology allows for the creation of very high quality fi bre composite elements, since it is possible to maintain a high volume of fi bre laying under constant tension. The process can also be automated. Spinning technologies require a high initial investment, but can also achieve relatively complex geometries using industrial robots.

15.12 Tape overlay process.

15.13 Spinning technology.

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15.4.4 Vacuum infusion process

In the vacuum infusion process, the fi bre sheets are placed in a ‘dry’ state with a plastic sheet laid over the entire form to create a vacuum. Resin is introduced at one end. The vacuum enables the fl ow of the resin and an even distribution of the matrix through the fi bres. In comparison with the hand laminating process, a higher volume of fi bre can be achieved in the composite material. However, it is diffi cult to control the fl ow of the resin along edges, corners, etc. It is also not possible to vacuum-infuse honey-comb materials for a sandwich structure.

15.4.5 Internal infl ation process

The internal infl ation process can only be applied in symmetrical hollow bodies composed of at least two halves or from one shell and one cover. In this process, each component is made using the hand-laminating process. A foil tube is laid in one half and partially infl ated. Then the halves are clamped together and the tube infl ated to 1–2 bars of pressure. Through this interior pressure, the exterior shells are pressed against their moulds and the laminate is condensed. The benefi t of this process is a higher inte-gration of the fi bres in the matrix, an increase of the fi bre volume percent-age and a reduction in excess matrix. This process enables an improvement in the quality of the fi nal product when compared to the hand-laminating process alone.

15.4.6 Carbon fi bre-reinforced polymer composites: mould heating process

Heated polymer moulds can be used in the creation of very large compo-nents. The electrical conductivity of carbon fi bres is used in order to heat the bearing layer of the mould during the casting process.

15.4.7 Tempering

It is important to consider tempering in any discussion about production, since it is with the help of tempering that the fi nal strength of the construc-tion element is achieved. Tempering enables an even integration of fi bres in the matrix. Tempering usually takes place at temperatures between 70 and 80°C in either:

• a tempering oven for small components,• a tempering chamber for mid-sized components, or• a tempering room/tent for large components.

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The temperature is achieved by various means, such as infrared lamps. Tempering is dependent upon the thickness of the laminate. Each milli-metre of thickness requires a tempering of around 1 hour.

15.5 Composites in building: the ‘Space Offi ce’

prototype

15.5.1 Introduction

The planning process for a ‘small prototype offi ce building in composite technologies’ has led recently to an offi cial application to build a ‘Space Offi ce’ (SO) at the home of Fritz Gampe, former member of the European Space Agency’s (ESA) Research and Innovations Group. The offi ce build-ing, planned as a showcase of capabilities in building with fi bre composite technologies, is seen as a smaller version of the ‘Space House’ concept developed by the ESA for a stable, lightweight and transportable building design that might be used in potential space colonies on the Moon or Mars. The concept was later re-evaluated for possible use for temporary buildings to help with natural disasters such as the Izmir earthquake in Turkey in 1999 and the Haitian earthquake in 2009. The SO has also developed from other projects such as the German Antarctic Polar Research Station Neumeyer III, designed as a composite structure for the Alfred Wegener Institute for Marine Research in Bremerhaven, Germany, and funded by the ESA (Figs 15.14 and 15.15). The project has been through a process of fi nite element modelling of the design and is currently awaiting fi nal approval by the planning authorities, before starting construction during 2010.

15.5.2 Materials

The objective is to build the SO entirely from ‘fi bre composite technolo-gies’, deliberately using a mixture of technical and natural fi bres and associ-ated resins and hardeners to gain experience with this type of technology for housing purposes. The prototype will be used to test the capabilities of these materials and related construction techniques.

The SO is designed to be built primarily from carbon-fi bre reinforced polymer (CFRP) composites and its sister material, basalt-fi bre reinforced polymer (BFRP) composites. It serves the purpose of getting realistic basic data for a new building technology in terms of material suitability and long-term behaviour, quality of living and aesthetics, environmental and health qualities, and last but not least, future building certifi cation and regulatory issues. Establishing the carbon footprint of lightweight fi bre technologies compared with heavy, conventional building materials suggests that the

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15.14 Neumayer III station, in cooperation between ESA (European Space Agency) and AWI (Alfred Wegener Institute).

15.15 Neumayer III station.

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former are more environmentally friendly, based on the energy and resources required to produce each type of material and produce compo-nents from them. Further work still has to be done, however, on life-cycle analysis for composite building materials of different kinds.

Carbon fi bres in conjunction with phenol resins are seen as providing the optimal ‘lightweight’ solution. Since phenol resins are not fl ammable or toxic and do not fume much when heated, composites using these resins meet requirements for fi re-retardant materials in buildings. Basalt fi bres offer a very promising alternative to glass fi bres in terms of availability and costs. Used with phenol as resin, similar fi re-resistance behaviour can be achieved. In addition, the UV sensitivity of basalt fi bres is much lower than that of other technical fi bres. Surface coatings will, however, be necessary to protect exterior composite panels from solar radiation, temperature fl uctuations and moisture to ensure their long-term stability and prevent micro-cracking. Using these lightweight materials, with a usable fl oor space of some 40 m2, the SO will have a total mass of less than 5000 kg, signifi -cantly less than if built with any conventional material.

Core materials for composite sandwich components are foams such as those based on polyvinyl chloride (PVC). Those appropriate for the SO are high-quality PVC foams which show good long-term performance, are easy to work with, are very lightweight and show very good thermal insulation with low thermal conductivity. The core material selected will be from certifi ed ‘closed cell’-type foam with technical characteristics as follows:

• Specifi c mass: 60 kg/m3

• Thermal conductivity: 0.032 W/mK• Melting temperature: around 100°C up to 250°C, improving resistance

to fi re hazards.

The use of sandwich components and multiple layers provides a ‘double wall’ which enhances both strength and safety (Fig. 15.16). The double wall

Protective cover (gel coat, UV-absorption, colour)

Load-carrying structure (fibre laminate, 1 mmthick)

Load-carrying structure (fibre laminate, 1 mmthick)

Fibre barrier (intumescent cork)

Inside

Outside

Core (high-tech foam, some 70–100 mm thick)

15.16 ‘Space Offi ce’ wall concept.

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design would protect the building in a fi re, even when the fi rst carbon-fi bre layer has been burnt away.

Natural fi bres will only be used in secondary structural parts like doors or interior panels. Cork, for example, could be applied as an inside layer to provide an additional fi re barrier. It has also been suggested as a fl oor material, given its sound attenuation properties. The contact surfaces between the SO legs and the ground could also include compression-stable cork.

Manufacturing and assembly of the individual segments will be done manually to ensure effective quality control and to be able to accommodate late design and material changes. Instead of a negative form, a positive mall will be used. The hand lay-up process will start with the inner foam layer and work to the top of the complete composite sandwich which will be fi nalised by applying the inner fi bre layer.

15.5.3 Design

The SO has a round, free-form look and stands on four detachable legs. It is not fi xed into prepared foundations like a standard building, but posi-tioned on unprepared ground using its four legs. In the event of high winds, it will be necessary to secure the house by additional means (similar to the way a tent is secured using ropes and pegs). The main dimensions are as follows:

• Radius: 6.5 m• Height: 5 m (the supporting legs will raise the offi ce 2 m above the

ground)• Offi ce fl oor: 40 m2 (usable volume: 300 m3).

Figures 15.17 and 15.18 show the fl oor plan and sections.Discussions with a large insurance company led to consideration of

potentially adverse weather conditions as a result of ‘global warming’. This included a design able to withstand a 210 km/h wind gust for 10 s. This suggested a disc-like design less vulnerable to wind gusts. Raising the build-ing on legs also took into account the potential risk of fl ooding. The design allows for fl ooding reaching a height of 2.5 m, covering some 98% of current fl ooding scenarios. The SO has also been designed with the poten-tial to use solar power to reduce its carbon footprint.

Fibre composite sandwich elements as primary structural elements require a new approach for the architect and the building engineer. Architectural design is still heavily infl uenced by ‘fl at-plate’ design, e.g. the use of fl at, rectangular walls. A ‘fl at’ plate, however, is in structural, load-carrying terms, a very ineffi cient design. Self-supporting natural structures like a turtle’s shell or a human skull are all naturally optimised to ensure

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15.17 ‘Space Offi ce’ fl oor plan.

15.18 ‘Space Offi ce’ sections.

that a minimum of material at a minimum weight gives maximum ‘func-tional support’. Lightweight composite structures require the use of mainly self-supporting, shell-type components to produce a rounded rather than a rectangular shape.

Using composites also requires an ‘integrated design’ approach to the manufacture of components which builds in strength, thermal protection, fi re resistance, UV protection, etc., in one go as part of the manufacturing process. In any optimised, lightweight structure (e.g. a satellite or racing boat), any existing ‘auxiliary structure’ has to contribute preferably in a multi-functional way to the fi nal goal. This requires integrating services such as electricity into the overall structural design. In the SO electrical and IT wiring can be housed in triangular-shaped tubing systems which can also add to the strength of the structure. Furniture can also be designed as

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load-carrying structural elements. Bookshelves, sideboards, tables, beds or built-in kitchen elements can all contribute to the overall strength of the structure.

Based on research by the European Space Agency (ESA), and the OMNIUM housing project in The Netherlands, the key assumptions for loads, safety factors and service life have already been established. The loads listed below will be used to verify the design by a FEM analysis (using the CATIA program) which will then be used to construct the individual load-carrying elements of the SO:

• Total weight (preliminary calculations): = 50,000 N with an assumed 3000 kg for the composite parts

• Operational fl oor load (meeting room) = 3000 N/m2

• Maximum wind loads, assuming a 210 km/h wind gust for 10 s (MuRe value):– front: 1200 N/m2

– rear: −750 N/m2

– side: −1000 N/m2

• Snow loads: 1100 N/m2 (to be reviewed depending on the site).

FEM analysis will establish the approximate thickness of carbon-fi bre panelling required to meet overall stress requirements (expressed in g/m2). It will also establish the quality of carbon fi bres required (expressed typi-cally in terms of HT(A/S), UM, etc.) as well as their orientation (e.g. single- or multi-directional layer). Further analysis will identify in which areas the carbon-fi bre thickness can be reduced to 50% if required, with local rein-forcements applied to meet stress levels. This analysis can also help estab-lish where carbon-fi bre composites can be replaced by basalt-fi bre composite components. As an example, FEM analysis would reveal that, based on the chosen wall design concept, a 4 × 400 g/m2 multi-layer carbon HT-fi bre would achieve the required strength. It would also highlight those areas which would need

• more or less strength in steps of a 200 g/m2 multi-layer• extra strength in terms of local reinforcements.

All these fi ndings will need to be followed up by tests. Based on this FEM analysis, proper testing and careful control of component manufacture and construction, the safety factor can be set to Sf = 2.0.

One important consideration is the likely service life of the structure. The use of FRP composites in buildings now goes back almost 40 years. Visiting one of the earliest examples, the range of ‘Futuro’ houses built by Matti Suuronen in Finland, highlights the importance of the quality of materials and the manufacturing process for composites. Based on this evidence, the ‘operational lifetime’ for the main structural parts of the SO is set to be 30

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years. To test this prediction, the building will incorporate monitoring systems for the degradation of the structural strength of the main compo-nents as the building ages.

15.6 Composites in buildings: The Walbrook, London

15.6.1 Introduction

The Walbrook (Figs 15.19 and 15.20) is an offi ce headquarters building by the architects Foster and Partners, situated in the heart of London. It occu-pies virtually the entire side of a city street and is one of the largest sites of its kind in the City of London. The building comprises 445,000 sq ft of offi ce and retail accommodation, including 410,000 sq ft of offi ces incorpo-rating trading fl oors, plus retail and restaurant accommodation amounting to 35,000 sq ft. The building is planned to be completed in 2010. Key part-ners are:

Client: Minerva plc, LondonArchitect: Foster + Partners, LondonFacade consultant: Arup Facade Engineering, LondonGeneral contractor: Skanska Construction UK, LondonFacade system: Josef Gartner GmbH, Gundelfi ngen, GermanyFacade components: Fibertech group GmbH, Chemnitz, Germany

The facade construction is unusual due to its use of a series of horizontal glass fi bre reinforced polymer (GFRP) composite ribs supported by vertical

15.19 View of The Walbrook, London.

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trunks. These protruding ribs provide a kind of fi lter in front of the glass facade, giving the rooms shade. The ribs also have an aesthetic function, following the contours of the facade, which curves inwards towards the top of the building, and becoming thinner towards the top of the building, thus increasing the sense of height. The ribs and trunks are self-supporting ele-ments with the ribs transferring load to the trunks.

The ribs are divided into several groups:

• EWS01 ribs in the lower part of the facade. At this point the facade is vertical.

• EWS02 ribs in the upper part of the facade. At this point the facade is at an angle to the vertical.

• EWS01 trunks connecting the ribs and transmitting the loads from the ribs to the facade and the main building structure.

• EWS02 casings for the trunks in the lower section of the building.

With the help of 3D CAD, the ribs have been manufactured with an ellipti-cal shape at widths of 200, 350 and 500 mm. Altogether, the 200 mm ribs have been manufactured in lengths of 1685 m and 900 m, divided into 576 and 336 pieces. Of the 350 mm ribs, 7270 m ribs have been produced, divided into 2752 pieces. Of the 500 mm, 2670 m ribs have been produced, divided into 1024 pieces. In total, a length of 12,525 m ribs have been

15.20 Street view of The Walbrook.

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produced and installed at The Walbrook. The trunks are manufactured at a length of 1080–5925 mm. Figure 15.21 shows a cross-section.

15.6.2 Materials

The ribs were manufactured from FRP composites. The laminate used glass fi bres in tissue form and rovings as additional reinforcement, embedded in a matrix of unsaturated polyester (PU) resin. A gel coating provides protection.

The following types of laminate were used, following the DIN 18820 Part 2 classifi cation:

• M2: matt/tissue 450 g/m2

• MW1: matt/tissue 450 g/m2 and woven fabric 580 g/m2, alternating• FM3: matt/tissue 225 g/m2 as exterior layer (for the achievement of a

smooth surface), followed by matt/tissue 450 g/m2 and roving 860 g/m2 (UD roving), alternating.

(M stands for cut fi bres used as bound matts; MW stands for a composite of matt and woven fabric; FM stands for a composite of matt and unidirec-tional fi bres). These laminates were tested in a laboratory before use.

The following matt/tissues were used in the laminate:

• Matt/tissue 450 used for M2, MW1 and FM3• Matt/tissue 225 used for FM3.

The fi bre matts were made from cut E-glass spun fi bres. The bonding used was a powderised, polyester-based matt binder which is easily soluble in styrol. The cut textile matt can be used in polyurethane, epoxy and vinyl

GFRP

200 mm

Connector

Façade

15.21 Cross-section of The Walbrook.

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resins. The thickness of the inlay was approximately 40 g/m2. Other ele-ments of the specifi cation were:

• Net weight 225 g/m2 and 450 g/m2

• Filament diameter 11 μm• Spun fi bres 12.5 tex.

Roving 870 (according to DIN 18820) was used for FM3. The chosen woven fabric UD0°, 870 g/m2 consists of glass fi bres plain woven in both warp and weft directions with edges fi xed by mechanical bond glass thread. The specifi cations were:

• E-glass roving, in warp (0°) direction: 21 ends/10 cm, 756 g/m2 areal weight, tolerance ±5%

• E-glass roving, in weft (90°) direction: 19 ends/10 cm, 114 g/m2 areal weight, tolerance ±5%

• Colour: white• Melting point (extent): ca. 1250–1600°C• Softening point: 825–225°C• Measure weight: 2590 kg/m3

• Flash point: non-burning• Electrical conductivity: electrical insulator• Solubility in water: insoluble• Explosion risk: not applicable• Oxidation risk: not applicable.

Woven fabric 580 was used for MW1. The chosen woven fabric ST0°, 580 g/m2 consisted of glass roving fi bres in both warp and weft directions constructed in a plain weave with edges fi xed by mechanically bonded glass thread. The product specifi cation was:

• E-glass roving, in warp (0°) direction: 25 ends/10 cm, 300 g/m2 areal weight, tolerance ±5%, fi bre tex 1200

• E-glass roving, in weft (90°) direction: 23 ends/10 cm, 276 g/m2 areal weight, tolerance ±5%, fi bre tex 1200

• Total areal weight 600 g/m2 ±5%.

For high-stress building components, for example the 500 mm ribs and the trunk connectors, higher-quality laminates were used. Pressed laminates with a fi bre volume of 60% were used for end-plates connecting trunks to the load-bearing structure.

The matrix chosen was PU resin as set out in DIN 16946 Part 2. The resin–glass ratio was 2.8 : 1; the hardening time was 24 h at 20°C and, after tempering, a minimum of 3 h at 80°C or 15 h at 50°C. These resins provide the product with high fl exibility and adhesion. Since easy application was needed, it was useful to have a product with a thin glass reinforcement. The

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low shrinkage allowed the application of fairly high thicknesses where needed, without the risk of excessive over-heating or breaks. The laminate was covered with a gel coat of thickness 0.5 mm to provide good resistance to weathering.

Tension tests according to DIN EN ISO 527 were carried out on the laminates with six tests per series to determine their tensile strength, the tensile e-modulus and the breaking point. Measurement of stretch charac-teristics was made using a video extensometer under standard weather conditions (23 ± 2°C, 50 ± 5% relative density) according to DIN 50014-23/50-2, i.e. three measurements, ±0.01 mm exactness. For the determina-tion of the force–tension range, the e-modulus was between ε′i = 0.05% and ε″2 = 0.25%. Wind and snow loads were calculated as vertical loads. Other temporary loads have also been calculated as vertical pressure loads. An example for a rib type 350 is shown in Fig. 15.22.

Shearing stiffness was tested according to DIN EN 6060 with six tests per series under normal weather conditions (23 ± 2°C, 50 ± 5% relative humid-ity), as set out in DIN 50014-23/50-2, i.e. three measurements, ±0.01 mm exactness.

Pressure-thrust tests were carried out according to ASTM D 7078 with six plus two tests in each series to determinate stiffness, breaking load, modulus and deformation under normal weather conditions (23 ± 2°C, 50 ± 5% relative humidity) as set out in DIN 50014-23/50-2, i.e. three mea-surements, ±0.01 mm exactness, modulus γ ′ = 0.001 and γ ″ = 0.005.

The laminate fulfi lled heat deformation resistance class A 90 with a temperature limit of 130°C classifi ed under the fl ammability classifi cation of DIN 4102-1 B2 – DIN EN 13501 / B s2 d0. The reduction factors in calculating load capacity were in accordance with DIN 18820. The safety factor S0 is in accordance with the guidelines for wind-farm composite materials (Germanischer Lloyd – Richtlinie für die Zertifi zierung von Windkraftanlagen).

V2L11C1

V2L11C1

X

X

ZZ

(a) (b)

YY

15.22 3D calculation model of the ribs type 350: (a) general view; (b) detail.

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15.6.3 Production and assembly of the composite components

Figure 15.23 summarises the production scheme. Tissue/matt, roving and woven fabric were laminated by hand using individual cutting patterns, models and moulding forms prepared in advance. Since the design was done using 3D CAD technology, with the CAD data transferred straight into the production planning, the fi nal installation process yielded perfect results. In the fi rst stage, models were built as positives for the creation of the negative moulds, using either water jet or three-axis CNC-milling (Fig. 15.24).

Models of the straight wings were produced using water jet technology. Water jet-cut ribs of aluminium were placed at equal distances and the gaps fi lled with foam. Three-axis milling technology was used for the more com-plicated components. The open moulds were then cast from the positive models. The more complex the fi nal form, the more complex the mould. For this project, it was generally possible to create the moulds in two parts (see Fig. 15.25). The end-plate model and end-plate are shown in Figs 15.26 and 15.27.

Two options were considered in assembling the two halves of the ribs:

Cutting of thetextile glass roving

Lamination of the subshellLamination of the

upper shell

Lamination of thehead plates

Lacquering

Glueing of the head plates

Measuring and cut

Connection of upper shelland subshell, insertion of

reinforcing strips andsound-damping elements

Preparation of the cavities

Preparation of the resin

15.23 Production scheme.

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(a) (b)

15.24 Positive models produced by (a) water jet technology and (b) 3D axis milling technology.

15.25 Finished mould.

15.26 Models of the end-plates for the ribs.

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1. Laminating the two halves, sanding the connection surfaces, fi xing a connection tissue, followed by glueing (see Fig. 15.28).

2. Laminating the two halves, then using the internal infl ation process with wet-in-wet laminates (see Fig. 15.29).

The internal infl ation process (IIP) is an innovative production method able to optimise the quality of hand-produced laminates. It is critical that this process is used with wet-in-wet laminates, i.e. laminates that are not cured. In each mould, the laminate is laid in according to the laminate plan. Each side of the mould is over-laminated by 50 mm. In one of the halves of the mould, a long plastic sack is placed and slightly infl ated. The halves are then pressed together. The plastic sack is a continuous polyethylene tube which is cut approximately 30 cm over-length on each side of the mould and then sealed to allow for infl ation and measurement of the pressure. The infl ated pressure is 1–2 bar, depending on the size and type of the mould and the thickness of the laminate. By infl ating the sack, the base laminate binds with the over-laminate. By combining internal and external pressure, the lami-nate is compressed. The cast stays in the mould for 8 hours, requiring a certain number of moulds, depending on the number of components required. A hard wax is used to separate the cast from the mould. As a result of this process the two halves are fused together, and the fi bres are fully embedded and wetted by the matrix. The percentage of the glass fi bres in the matrix increases. The result is higher load capacity through higher density. This process has the following advantages:

• The production of each rib takes place in one stage.• The process is easily reproducible.

15.27 End-plates for the ribs.

��



15.28 Test stages of the production of a rib using choice 1.

• A continuous laminate is created within the rib.• Extra deposits of matrix do not occur.

Each component was tempered before lacquering. The duration of the tempering was quantifi ed according to the thickness of the laminates and the results of preliminary trials (approximately 1 h per mm thickness of laminate). The tempering took place in a tunnel with infrared heating at a temperature of 70°C.

Figures 15.30–15.34 show further construction processes and details of the end-plates and ribs.

Ribs of different length and curvature were manufactured with widths of 200, 350 and 500 mm. The ribs are connected to the trunks using special connection plates which form a dovetail in the rib, transferring the load. The dovetail also guarantees an accurate placement. The dovetail is attached to the rib with helicoil screws. The adhesion of the rib to the trunk was undertaken using a high-elastic fi bre-reinforced polyester resin which guar-antees high tension stability (45 N/mm2). The tension was calculated based on the lower shearing strength of the base material. This means that, in case of failure, the base material will fail before the adhesive. The trunk is screwed with an aluminium profi le at the rear. This L-formed aluminium element is responsible for the attachment to the load-bearing profi le of the

��



15.29 Sequences of the production of a rib according to choice 2, internal infl ation process.

facade and transfers all the vertical and horizontal loads. The lower con-nection of the trunks, made of an aluminium profi le as well, maintains the distance between the trunk and the facade profi le. The connection of the ribs to the front of the facade occurs either through the trunk which then transfers the loads to the facade, or through steel profi les which connect the ribs horizontally with the facade. The steel profi les were then encapsulated using GFRP coverings. These processes are illustrated in Figs 15.35–15.42.

The coatings for all GFRP facade components were specially developed by the manufacturer. The coating protects components from external impact, such as the impacts of birds or falling items, as well as UV radiation,

��


15.30 Sequence of the attachment of the end-plates. The tapped elements have been glued into the end-plates for the ultimate installation.

15.31 Construction process of the trunk: positive form, negative form, raw element, fi nal element.

��


15.32 Ribs of types 200 mm and 500 mm.

15.33 Rib element in the form.

15.34 The rib gaps are worked out with extraordinary accuracy.

��



15.35 Transfer part at the specifi ed trunk connecting type 500 and type 200 ribs. The aluminium connector is visible as well.

J.3Aluprofil 400 mm breitVerschraubung: 8*M10

Klebelasche analogKnotenbaum 200 mm

X

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15.36 3D-CAD planning of the transfer part at the specifi ed trunk connecting ribs type 500 and type 200.

humidity, etc. The gel coating is applied with spray guns. The lacquering is undertaken in three layers with the last layer as a transparent top-coat. The overall thickness of the lacquering is approximately 0.5 mm. This gel coating is a high-percentage resin based on acrylic. The coating was produced in the following steps:

• Filling with a two-component fi ller based on polyester• Sanding with 120 grain paper• Degreasing

��



15.37 Aluminium profi le at the rear of the trunk for transferring the loads.

• Light priming in three layers• Drying for 10 min (layer thickness ca. 90–105 μm), drying at 60°C for

60 min• Sanding with 400 grain paper• Filling with light fi ller• Degreasing• Lacquering in two to three steps• Drying for ca. 3–5 min• Transparent lacquering in two steps• Drying for 15 min, then oven-drying at 60°C for 60 min• Sealing at the edges, using UPS ferro-spray.

In order to ensure maximum durability against UV and other types of degradation, several long-term tests were carried out on the coatings (see Tables 15.4 and 15.5) . These tests included:

• Testing in humid conditions: 40°C at 100% RH for 240 hours• Testing for temperature fl uctuations: alternating cycle between −35°C

and 80°C for 1000 hours (Japanese Industrial Standard A 6090 Clause 6.9 (Thermal Cycling))

• Testing for UV radiation using BS EN ISO 11507: 4 hours exposure to a light with specifi ed UVA content at 60°C, followed by 4 hours expo-sure to a condensed atmosphere at 50°C for a period of 2000 hours

• Instrumental colour measurements prior to testing and after 2000 hours of UV exposure

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15.40 Steel profi les and rib in mock-up.

15.41 Laminate concept for ribs.

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15.42 Trunk before lacquering and in the fi nished state.

Table 15.5 Texts of the coating system, part 2

Test procedure Oil soot, 72 h RT

QUV test, 1000 h

Sulfuric acid, 10% 72 h RT

Cleaning agent, 72 h RT

Test result No change No change No change of the surface

No change of the surface

Result of primer basic lacquer varnish

OK OK OK OK

Table 15.4 Tests of the coating system, part 1

Inspection method

Steam jet test PV 1503

Behaviour in KK, 40°C, DIN50017, 240 h

Change of climate, PV 2005A

Behaviour at chill impact test, ISO 4532

Pancreatin, 72 h RT

Inspection result

No fl aking of the lacquer


No fl aking or cracks


Result of primer basic lacquer varnish

OK OK OK OK OK

• Steam jet test according to TL 211• Freeze–thaw testing: 10 cycles with 18 hours immersion in water at 20°C,

followed by 3 hours at −30°C, followed by 50°C.

Several mock-ups were used to verify the assembly and installation steps (Fig. 15.43):

• Visual mock-up (Fig. 15.44): for clarifi cation and verifi cation of the visual appearance

��



15.43 Assembled parts, ready for delivery (left) and installation (right).

• Performance mock-up: for verifi cation of the attachments, gaps, load transmission, functionality of the entire system, water sustainability and durability.

Completed elements were transported to the site and installed on the building. Additional visual examination was carried out during production, assembly at the factory and installation on site. The visual examinations were undertaken in parallel with other types of test, including adhesion tests. Additional tests were carried out to examine the rain and wind stability of the entire system (Fig. 15.45). For this purpose, ribs were

15.44 Visual mock-up.

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15.45 Wind and weathering stability tests (photos: Fa. Gartner).

placed with their original connectors and trunks on the facade. A propeller-generated wind with a strength of 10–12 bft was applied whilst water was also sprayed on the facade to simulate hurricane conditions. In addition the entire structure is now continuously monitored in situ. Fig. 15.46 shows the facade elements ready for delivery and Fig. 15.47 the fi nal street view.

15.7 Composites in buildings: The Feathered Wing,

Feuchtwangen, Germany

15.7.1 Introduction

Several cities in southern Germany founded in the Middle Ages have recently become well known as places for theatre festivals. One of the leading festival cities is Feuchtwangen in Bavaria. Since 1949 there has been

15.46 Facade elements ready for delivery.

��



15.47 Street view.

an annual open-air theatre festival during the summer months in the pic-turesque cloister of the Romanesque abbey. Since the temporary open-air stage no longer meets the standards required and needs better protection from the weather, a new stage with a convertible roof will replace the exist-ing structure in the summer of 2010.

In the new design, the stage will be covered by a feathered wing-like structure like a ‘landed bird’ with spread-out feathers (Fig. 15.48). Every summer, the wing will temporarily ‘land’ to provide protection for the theatre. The roofi ng system has been conceived as a reinterpreted bird’s wing composed of seven feathers, which, when spread, provides shelter from the elements for the theatregoers and, when tucked in, leaves the theatre exposed to the open air. It is designed to act as a sunshade or umbrella, depending on the weather, while also actively working to retain the charm of open-air theatre. Key partners are:

Client: City of Feuchtwangen, GermanyArchitect: Pohl Architekten Stadtplaner, Jena, GermanyStructural engineer: Knippers Helbig – Advanced Engineering, Stuttgart

and New York

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15.7.2 Design and materials

The fi rst component of the new structure is the arch framing the stage and the supports on each side. These are like the body and the skeleton of the bird. The second component is the roof itself, a foldable wing made of seven laterally sliding feathers manufactured from FRP composites. The wing can assume one of three predefi ned positions:

• In the spread position, the feathers create a closed roof that stops rain.• In the half-spread position, the feathers offer protection against the sun

while allowing the guests to enjoy a view of the abbey church.• In the tucked-in position, the feathers are tightly packed together and

entirely open the stage to the sky.

Each feather has regular rows of skylights made of semi-transparent panes that allow for an even, natural lighting of the stage and create a light, airy structure above the heads of the theatregoers. When the wing is spread, rainwater is channelled to gutters in the supporting structure, which then pass the water through downspouts in the rear beams to the drainage system.

Because of the seasonal use of the stage for theatre in the summer, and the annual logistical issues of installation, dismantling and storage, it was important to fi nd a simple method of construction. A logical and simple assembly and dismantling process was critical to the design. Once delivered to the town’s market square, a mobile crane lifts the individual elements into the abbey cloister. The crane is also used to help build the structure. The feathers, which are the largest individual components, are individually

15.48 Overview of the Feathered Wing, Feuchtwangen.

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15.49 Roof structure of the Feathered Wing.

transported and have been designed to be installed in less than one day. The overall installation is planned to take no longer than two days.

The decision to build with FRP composites was made easy because of the reduction of weight and simultaneous high degree of stability that can be achieved with these materials. The individual feathers function as single bearing elements and distribute their mass across two transport tracks. Their dimensions have been arrived at by fi nding the appropriate point between the distortion limits of the components and the useful surface area relevant to the site and needs of the space. Each of the feathers measures almost 19 m by 3 m and has a surface area of approximately 50 m2. When the wing is spread, the roof has a total surface area of 330 m2. The feathers have GFRP/CFRP main supports as well as GFRP ribs. The following materials have been chosen for the construction of the feathers. Laminates are constructed according to their stress-factoring as laid out in DIN 18820:

• Fibre laminate M1• Fibre laminate MW1• Fibre laminate FM3• Laminate main girder (upper section): carbon UD reinforcement.

The feather structure is regularly interspersed with triangular windows (Figs 15.49 and 15.50) which fulfi l four different functions:

• As optical elements they permit the passage of light through the spanned wing.

• They lower the overall weight of the structure.• As load transferring members they provide structural reinforcement.• Their design echoes the design of the cloister.

Their design is therefore a combination of aesthetic considerations and functional requirements.��


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In section, the feathers (Fig. 15.51) have an aerodynamic form and are curved at the trailing edge like the bow of a violin. The leading edge of the feather is only 50 mm thick. Just before the curve arrives at the main ‘beam’, it is 290 mm in height. This beam-like structural component ulti-mately rises to 430 mm before sharply trailing off. PUR foam is used to fi ll the space between the upper and lower laminate layers.

Using calculations of the force distribution in the movement system and the joints (Fig. 15.52), the level of force needed was optimised and critical gradients minimised to ensure the roof operated smoothly. Each feather slides and rotates perpendicular to its length at a constant speed along the track via rollers attached on the underside of the track (see Figs 15.53 and 15.54).

The roof construction is placed in the cloister with walls on all sides and is therefore protected from wind to a great degree. However, the western wall of the garden is lower than the upper edge of the track, which requires the inclusion of wind suction in the calculation of the potential strain on the roof. Therefore, understanding wind loads is decisive. Since the poten-tial wind load for such structures is not well covered in the literature, the theoretical values have been appraised according to standard wind load values. In this way it is possible to guarantee an appropriate dimensioning of the roof’s bearing structure. With regard to the three different positions that the wing can take, loading situations are individually calculated as follows:

• Wing fully spread: the leading feather is locked into position, in order to prevent an unplanned opening via a gust of wind.

• Wing tucked in: the leading feather is also locked into position, in order to prevent any unplanned movement of the wing.

• Wing half spread: the wing will be completely closed at a wind-strength of 6 Beaufort (12.3 m/s).

In Feuchtwangen snow loads are to be applied as Zone II according to DIN 1055-5 (07.2005). However, it is assumed that, since the roof is installed

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15.54 States of the Feathered Wing.

at the end of April and dismantled at the latest at the end of August, no snow loads have to be calculated. With regard to fi re risk, the feathers are classifi ed according to B1 S2 d0 of DIN 4102 and EN 13501-1.

The laminate components of the feather section are shown in Fig. 15.55 and Fig. 15.56 shows an overview of the fi nished structure.

15.8 Acknowledgements

Information and tables have been provided by Fibretech Composites GmbH, Jens Brandes, www.fi bretech-composites.de; and Fiber-Tech Group, Matthias Pfalz, www.fi ber-tech.de.

��



15.55 Feather section laminate components.

15.56 Overview of the Feathered Wing, Feuchtwangen.

Discussion of Space Offi ce

Text by Fritz Gampe and Göran PohlAll fi gures and tables by Fritz Gampe, HTS GmbH, Coswig/Dresden, and S.E.C.-Consulting, Uckerland, Germany

Discussion of The Walbrook

Text by Matthias Pfalz and Göran Pohl

��



Information provided by Fiber-Tech Group, Matthias Pfalz, www.fi ber-tech.de

All fi gures and tables by Fiber-Tech Group, www.fi ber-tech.de

Discussion of Feathered Wing

Text by Göran PohlFigures by Pohl Architekten, www.pohlarchitekten.deFigures 15.53 and 15.54 by Knippers Helbig Advanced Engineering GmbH,

www.khing.de

15.9 Bibliography

[1] Funke, H., 2001. Systematische Entwicklung von Ultra-Leichtbaukonstruktionen in Faserverbund-Wabensandwichbauweise am Beispiel eines Kleinfl ugzeuges. Rheda-Wiedenbrück, Germany.

[2] Michaeli, W., Wegener, M., Begemann, M., 1989. Einführung in die Technologie der Faserverbundwerkstoffe. München, Wien: Carl Hanser Verlag.

[3] Michaeli, W., Huybrechts, D., Wegener, M., 1994. Dimensionieren mit Faserverbundkunststoffen, Einführung und praktische Hilfen. München, Wien: Carl Hanser Verlag.

[4] Puck, A., 1996. Festigkeitsanalyse von Faser-Matrix-Laminaten, Modelle für die Praxis. München, Wien: Carl Hanser Verlag.

[5] R&G (ed.), 2009. Handbuch Faserverbundwerkstoffe, 8th edn. Waldenbuch, Germany.

[6] VDI (ed.), 1997. VDI 2014, Blatt 3 (Entwurf): Entwicklung von Bauteilen aus Faser-Kunststoff-Verbund, Berechnung, Verein Deutscher Ingenieure, VDIGesellschaft Kunststofftechnik. Berlin: Beuth-Verlag.

[7] Garner, P., 2008. Sixties Design. Köln: Taschen. [8] Van Uffelen, C., 2008. Pure Plastic: New Materials for Today’s Architecture.

Salenstein, Switzerland: Verlagshaus Braun. [9] AVK – Industrievereinigung Verstärkte Kunststoffe e.V. (ed.), 2010. Handbuch

Faserverbundkunststoffe: Grundlagen, Verarbeitung, Anwendungen, 3rd edn. Wiesbaden: GWV Fachverlage.

[10] Genzel, E., 2006. Zur Geschichte der Konstruktion und der Bemessung von Tragwerken des Hochbaus aus Faserverstärkten Kunststoffen 1950–1980, PhD Bauhaus-Universität Weimar.

[11] Voigt, P., 2007. Die Pionierphase des Bauens mit Glasfaserverstärkten Kunststoffen (GFK) 1942–1980, PhD Bauhaus-Universität Weimar.

[12] CTM (ed.), 2005. CTM Composite Leitfaden, http://www.ctmat.de/downloads.htm?dgroup=31

[13] R&G (ed.), 2009. Faserverbundwerkstoffe Composite Technology. Handbook, http://download.r-g.de/handbuch_edition_06_09.pdf

[14] Flemming, M., Roth, S., 2003. Faserverbundbauweisen. Berlin: Springer-Verlag.

[15] Schürmann, H., 2005. Konstruieren mit Faser-Kunststoff-Verbunden. Berlin: Springer-Verlag.

��



[16] Pohl, G., 2009. Konstruktionsprinzip Effi zienz, VDI-Tagung Bauen mit Innovativen Werkstoffen, VDI Wissensforum.

[17] Pohl, G., 2009. Konstruktive Architektur – Leicht und Weit, pp. 69–93 in: Baier, B., Reichweiten – Leichte Konstruktionen. 5. Interdiszipläres Symposium Essen für konstruktive Gestaltung und Leichtbau. Verlag der Universität Duisburg-Essen.

[18] Otto, F., 2005. Frei Otto – das Gesamtwerk – Leicht bauen, natürlich gestalten. Basel: Birkhäuser.

[19] Müller, L. (ed.), 2007. R. Buckminster Fuller. Your Private Sky. Design als Kunst einer Wissenschaft. Baden, Switzerland: Verlag Lars Müller.

��


471

Index

ACI 440.1R-03, 82, 115ACI 440.2R-02, 89, 100ACI 440.R-07, 82, 84, 115ACI 440.1R-03 2003, 91, 116ACI 440.2R-02 2002, 91ACI 440.7R-10 2010, 114acrylates, 36, 342acrylic, 180acrylic lacquers, 55–6Airex, 431airtecture, 195alkali-resistant glass fi bres, 75Allianz Arena, 416allowable stress design, 119aluminium, 429anticlastic, 233, 239antifungal fi nishing, 26antimicrobial fi nishing, 26antistatic fi nishing, 26aramid fi bres, 9, 27, 75, 130, 427–8architecture

tensile textiles structures, 229–54applications, 244–8common materials and architectural

properties, 240–4design development, 233–9fabric architecture concept, 231future trends, 252–4general principles, 231–3history and development, 230

Artec, 425artifi cial fi bres, 52Arundo donax, 295, 297, 300ASD see allowable stress designASTM D 7078, 446atlas weaving, 53atmospheric plasma, 46–7Australian Institute of Architects, 400autoclave technique, 433

Baader Wertpapierhandelsbank, 387textile lamellars opening, 388

backscattered light, 345–6

Baden-Württemberg Competence Network Biomimetics, 294

balanced failure, 116balsa wood, 430basalt-fi bre reinforced polymer, 436basalt fi bres, 429, 438Basilica of St. Francis of Assisi, 112Bernoulli fl ow, 265BFRP see basalt-fi bre reinforced

polymerbiaxial tear tests, 139–41

cut in the middle of the fi eld, 140bicomponent fi bres, 18bicomponent spinning, 17–18Biokon International, 294, 312biomimetic textiles, 253biomimetics

applications in architecture, 318–21fi bre-reinforced wood trunk

section, 320self-repairing biomimetic membrane

for pneumatic structures, 319–21

technical plant stem, 318–19wooden tubes, 319

future trends, 321–6Actinoptychus diatom, 322Arachnoidiscus diatom, 323Arachnoidiscus diatom 3D

analysis, 323biomimetics potentials and

limitations, 326Coscinodiscus wailesii diatom 3D

analysis, 324hierarchical structures as optimisation

strategy, 322–5hierarchical structures using carbon

fi bre reinforcement, 325new implementations of biologically

functional principles, 321shell diatom 3D analysis, 324transferring hierarchical

structures, 326

472 Index


methodology in architecture and engineering, 312–18

bottom-up approach by technical plant stem, 313

bottom-up approach in bionics and biomimetics, 313–14

bottom-up vs top-down approach, 315–16

extended top-down approach, 316pool research, 316–18pool research infl uence, 317top-down approach, 314–15top-down approach by shock absorbing

transportation pallet, 314textiles solutions for construction,

310–26biomimetics, bionics and technical

biology defi nitions, 311–12natural development benefi ts for

technical purposes, 312biomimicry, 381–95

cactus fl eshy ribs shading effect, 382simplifi ed penguin feather, 387ventilation principle in burrow of black-

tailed prairie dog, 389BIONA, 318bionic self-repairing coatings, 320bionics, 311BIPV see building integrated

photovoltaicBird’s nest, 247Boltzmann constant, 162Boltzmann laws, 161–2bottom-up approach, 313–14Boyle–Mariotte gas law, 217Bragg grating, 337braid-pultrusion technology, 299, 301braided fabric, 31braiding machine, 302Brillouin frequency shift, 346Brillouin scattering, 346, 347building integrated photovoltaic, 364building textiles, 15

see also fabric facadebuilding up air cavities, 394buildings

constructive formation with textiles, fabrics and sheeting, 5–6

fi bre reinforced polymer compositedesign and manufacture, 431–6materials, 69–123

textilestechnical characteristics and

requirements, 49–67types and production used, 13–47

see also sustainable buildingsBurj Al Arab Hotel, 416bursting test, 139, 144butterfl y’s wing, 321

cable edge test, 149CAN/CSA-S6-00 2000, 89, 91CAN/CSA-S806-02 2000, 91CAN/CSA-S806-02 2002, 91canvas weaving, 53CAO see Computer-Aided Optimisationcapillary rise test see wicking testscarbon fi bre reinforced polymers, 436

automated device for pre-tensioned strips application, 122

fabrics application for concrete columns confi nement, 107

L-shaped strips, 106, 107reinforcement in Wotton bridge deck, 117seismic retrofi tting, 113, 114

carbon fi bre reinforced polymers jackets, 105

carbon fi bres, 9, 29, 75, 428–9, 438carbon rods, 306carbon tower, 291catenary, 232CATIA program, 441cellulose fi bres, 25Center for Synergetic Structures of the

Eidgenzössische Materialprüfanstalt (EMPA), 320

CFRP see carbon fi bre reinforced polymersChroMyx, 253classical laminate theory, 80coatings, 35–8, 58–61

developing and testing for tensioned membrane structures, 129–85

chemical, light and fi re durability of membranes, 172–6

heat and energy transport in membranes, 155–71

light transmission through membranes, 154–5

material systems used for membranes, 129–32

mechanical tests and behaviour of membranes, 134–42

strength of connecting systems for membranes, 142–53

surface cleaning properties of membranes, 177–85

test methods and characterisation of membranes, 132–4

materials, 130–1solar functions in construction, 154

coconut fi bres, 10, 429cold temperature hardening prepreg

system, 433compensation, 237composite laminates

theoretical and experimental determination of mechanical properties, 79–82

geometry and co-ordinate system, 81

Index 473


composites, 290–1durability, 83–91

compression failure, 116Computer-Aided Optimisation, 324computer-controlled braiding techniques,

297confi nement, 107–11confi ning pressure, 110conifer wood, 295construction

ethylene-tetra-fl uorine-ethylene-foil, 189–226

construction methods and types, 190–2

development potential, 219–20future requirements for architecture

and civil engineering, 220–3historical development, 193–202load-bearing behaviour, 215–19material properties, 210–15typology, basic shapes and application

range, 203–5fi bre reinforced polymer composite

materials, 69–123textile types and production used,

13–47textiles in providing biomimetic

solutions, 310–26biomimetics, bionics and technical

biology defi nitions, 311–12biomimetics applications in

architecture, 318–21future trends, 321–6methodology in architecture and

engineering, 312–18natural development benefi ts for

technical purposes, 312see also lightweight constructions

copolymers, 205cotton, 27cotton fi bres, 17creep rupture, 87cross-weaving, 53

D-SET laboratories, 213deformation behaviour, 134, 149–53

biaxial, parallel thread tests, 149–51creep, 153relaxation behaviour, 153shear behaviour, 151shear modulus determination, 151shear stiffness determination, 153

DesignInc, 384dimensioning, 431–2DIN 4102, 62, 276, 467DIN 7724, 207DIN 7728, 206DIN 16946, 445DIN 18820, 444, 445, 446, 463

DIN 53354, 136, 138, 139, 142, 143, 144, 146, 147, 148

DIN 53363, 140, 141DIN 53861, 139DIN 1055-5, 465DIN 4102-1, 211DIN 5031-7, 211DIN 13934-1, 136, 138, 139DIN 52861-3, 144DIN 50014-23/50-2, 446DIN 4102-1 B2, 446DIN EN 6060, 446DIN EN 13501, 446DIN EN 24920, 177DIN EN 53924, 174DIN EN 20105 A03, 177DIN EN ISO 62:2008, 213DIN EN ISO 527, 446DIN EN ISO 4892, 172, 173DIN EN ISO 13823, 176DIN EN ISO 4892-3:2006, 213DIN EN ISO 11925-2, 176DIN EN ISO 105-B01, 173DIN EN ISO 105-B02, 173DIN EN ISO 105-B06, 173dirt repellence, 25distributed strain sensing, 345double-glazed facades, 401–4double T-beams, 298downcycling, 214, 221dry application, 91dry spinning, 22dry-wet spinning see gel spinningductility, 101duroplastic, 424Dutch rush see Equisetum hyemaledynamic relaxation, 235Dyneema, 4, 10Dyneon, 57

E-glass fi bres, 57, 73, 427EBFR see externally bonded fl exural

reinforcementEBSR see externally bonded shear

reinforcementEero Aarino, 9Eero Saarinen, 9Egg garden chair, 421elastic modulus, 152embodied energy, 378EN 13501-1, 467EN ISO 1182, 176EN ISO 1716, 176energy concept, 283–4environmental reduction factor, 89epoxy resins, 76–7, 425Equisetum hyemale, 295, 297, 298ESA see European Space AgencyETFE see ethylene tetrafl uoroethylene

474 Index


ethylene, 208ethylene tetrafl uoroethylene, 5, 266, 269,

351, 377foils, 34, 41, 189–226, 407–9

challenges in using in architecture, 398–418

typical infl ated foil cushions, 408vs double-glazed facade material

properties, 409–12vs PTFE and double-glazed facades

energy-effi ciency attributes, 401–4ETTLIN lux, 253EU Building Products Guidelines, 132, 133European Design Guide for Tensile Surface

Structures, 231European Space Agency, 422, 441

Research and Innovations Group, 436expanded polytetrafl uoroethylene fi bres, 28externally bonded fl exural reinforcement,

94–5accidental situation verifi cation, 101debonding failure modes, 96serviceability limit state verifi cation,

100–1externally bonded shear reinforcement, 102

accidental situation verifi cation, 107fatigue, 107serviceabilitity limit state verifi cation, 106ultimate limit state verifi cation, 104–6

anchorage pullout of CFRP L-shaped strips, 106

opening of the overlapping of L-shaped strips, 106

peeling-off and CFRP plate fracture, 106

extrusion, 22

fabric facadeaim, objectives and methodology of the

study, 399–400application possibilities in Australia,

413–14architects’ opinions

ETFE facade material properties vs double-glazed facade, 410

importance of energy-effi cient energy facade material properties, 407

PTFE-coated fi breglass fabric, 409PTFE facade material properties vs

double-glazed facade, 411typical ETFE infl ated foil cushions, 408

challenges in using textile materials in architecture, 398–418

deliberations on future developments, 417–18

energy effi ciency-related issues, 406–12ETFE and PTFE facade material

properties vs double-glazed facades, 409–12

ETFE and PTFE foils, 407–9importance of energy-effi cient facade

material properties, 406–7ETFE, PTFE and double-glazed facades

energy-effi ciency attributes comparison, 401–4

experience of architects, 400, 405–6energy effi ciency and textiles, 405

results of the interviews, 400, 405–16summary of results, 416–17textile integration into energy-effi cient

buildings, 412–16fabrics, 130

coated, 58–61draft, design, computation, engineering

success, 65–6assembly, erection and dismantling, 66load bearing and shape fi nding of

membranes, 65–6existing concrete structural members

strengthening, 91–2historical development for use in

construction, 50–3fabric elements composition, 52–3fabrics from natural fi bres, 51fabrics from synthetic fi bres, 51–2

technical characteristics and requirements for modern structural engineering, 62–6

thermal and acoustic behaviour, 63–5blister foils and refl ecting layers

composite thermal insulation, 64energy conservation and production,

63–4environmental considerations, 65noise and sound control, 64–5thermal insulation, 63

uncoated, 56–8fi breglass fabrics, 57fl uoropolymer fabrics, 57–8polyester fabrics, 56–7

Fabry-Perot systems, 337fatigue, 87–8FBG see fi bre bragg gratingFeathered Wing, 460–7

design and materials, 462–7feather section, 465feather section laminate components, 468fi nished structure overview, 468kinematic system, 467movement study, 466new design overview, 462roof structure, 463states of the feathered wing, 467top view of the roof structure, 464

Fermat’s principle, 333fi b-bulletin-40, 115FiberlineComposites, 119fi bre bragg grating, 338

Index 475


fi bre composites, 290fi bre optic sensors, 334fi bre reinforced composites, 41fi bre reinforced polymer composites, 6–7,

70–1, 291, 421building and construction, 69–123

deterioration of columns due to corrosion, 70

historical background, 71–2importance in structural engineering,

69–71composites durability, 83–91

consideration in guidelines, codes and standards, 88–9

environmental reduction factors, 89fi re resistance, 89–91

concrete structural members strengthening, 91–101

determining shear stress between EBFR and concrete surfaces, 99

ductility, 101EBFR accidental situation verifi cation,

101EBFR debonding failure modes, 96EBFR serviceability limit state

verifi cation, 100–1fabric applications on masonry, 92fabric types, 92fabrics, 91–2fl exural strengthening applications, 94–5fl exural strengthening design, 95–100prefabricated CFRP L-shaped strip, 93prefabricated strips, 93–4prestressed systems, 94prestressing and heating device, 94pull-off test and corresponding strain

and shear stress, 97straight strip produced in pultrusion

process, 93confi nement, 107–11

applications, 107–8CFRP fabrics for concrete columns

confi nement, 107confi ning pressure due to confi nement

jacket, 110design, 108effect on stress-strain diagram, 109effectiveness, 111increasing axial strength, 109–11increasing concrete ultimate

compression strain, 109prestressed, 111prestressed confi nement using aramid

strips, 108constituent materials, material properties

and manufacturing, 72–83column wrapping using wet lay-up, 83common fi bres vs human hair

diameter, 74

composite laminates mechanical properties, 79–82

fi bre properties, 74fi bres, 73–6manufacturing techniques, 82–3matrix, 76–9multi-layer laminate geometry and

co-ordinate system, 81pultrusion machine devices, 83raw materials, 72–9reinforcing fi bres stress-strain

curves, 73thermoplastic matrices properties, 79thermosetting matrices properties, 78

core materialsfoam sandwich, 430honeycomb sandwich, 430sandwich construction, 429–30

design and manufacture for buildings, 431–6

hand laminating process, 432, 433internal infl ation process, 435mould heating process, 435prepreg process, 432–4spinning technology, 434tape overlay process, 434tempering, 435–6vacuum infusion process, 435

environments affecting durability, 84–8alkali effects, 85–6creep and relaxation, 87fatigue, 87–8moisture and solution effects, 84–5temperature, 86–7ultraviolet radiation, 88

feathered wing, Feuchtwangen, Germany, 460–7

design and materials, 462–7feather section, 465feather section laminate components,

468fi nished structure overview, 468kinematic system, 467movement study, 466new design overview, 462roof structure, 463states of the feathered wing, 467top view of the roof structure, 464

fi rst experiences with application up to modern buildings, 7–9

future developments, 121– 3automated device for application of

pre-tensioned CFRP strips, 122new material, 121–2prestressing technology, 122–3

historical background, 421–3gas station by Matti Suuronen near

Lempäälä, Finland, 423Tournesol, 422

476 Index


innovative composite-fi bre components in architecture, 420–68

internal reinforcement, 114–17applications, 116–17completed Wotton bridge, 117design, 115–16GFRP and CFRP reinforcement in

Wotton bridge deck, 117masonry structures strengthening, 111–14

carbon rods bonded into space between bricks, 112

castle and tower under strengthening and repair works, 113

seismic retrofi tting using CFRP strips, 114

seismic retrofi tting using GFRP fabric and CFRP strips, 113

materials for composites, 423–31Artec Exhibition room, 426carbon fi bre types qualities, 428e-fi breglass important characteristics,

427fi re-retardant composite materials,

430–1gel coat plus fi ller, 431matrix materials, 424–5production process, 424reinforcing fi bres, 425–9reinforcing fi bres tension–elasticity

relationship, 426thermoplastic and duroplastic

integration, 425various matrix materials overview,

424profi les, 118–20

conventional pultruded cross-sections, 118

GFRP profi le in noise barrier construction, 119

mechanical connections of laboratory bridge at Empa, Switzerland, 121

Pontresina bridge in Switzerland, 120shear and fl exural strengthening

due to new holes in a beam in a building, 101

with strips and fabrics in a cement factory, 102

shear strengthening, 101–7applications, 101–2design, 102–4EBSR accidental situation verifi cation,

107EBSR fatigue, 107EBSR serviceabilitity limit state

verifi cation, 106EBSR ultimate limit state verifi cation,

104–6load-strain diagram for shear

reinforcement, 103

principles, 102T-cross section geometry, 105

space offi ce prototype, 436–42design, 439–42materials, 436, 438–9

Walbrook, London, 442–60composite components production and

assembly, 447–60cross-section, 444materials, 444–6street view, 443view, 442

fi bre reinforced resins, 8fi breglass, 5, 6, 9fi breglass Bubble chair, 421fi breglass fabrics, 57fi breglass reinforced polymers, 8fi bres, 73–6, 130

changing properties by post-treatment and fi nishing, 23–6

antimicrobial and antifungal fi nishing, 26

antistatic fi nishing, 26dimensional stability, 24dirt and oil repellence, 25fi bre shape, 24fl ame retardance, 25–6fl at and textured fi laments, 24heat- and ultraviolet-protection, 25hydrophobic properties, 24

characteristics and properties, 17–22bicomponent fi bre types, 18chemical stability, 21–2cross-sectional shape, 17–18fi bre length, 19fi bre thickness/diameter, 18mechanical-physical, 19number of fi laments, 19properties in standard climate, 20surface-related properties, 20temperature resistance, 21thermal stability, 20–1

classifi cation, 16inorganic materials, 16materials for buildtech applications, 26–9natural fi bres, 15natural polymers, 15–16production, 22–3

cutting, 23dry spinning, 22gel spinning, 23melt spinning, 22stretching, 23twisting, 23wet spinning, 22

properties, 74synthetic polymers, 16

fi lament winding, 82–3fi nite element analysis, 324

Index 477


fi nite element computing methods, 294fi re resistance, 89–91

issues related to fi re effects on FRP systems, 90–1

bond properties at elevated temperatures, 90

current treatment in codes and guidelines, 91

fi re tests, 90–1fl ame spread, smoke generation and

toxicity, 90strength and stiffness at elevated

temperature, 90standards, 175

fi re retardant composite materials, 430–1fi re retardants, 25–6, 244fi re tests, 174–6fl at knitting, 30fl at-plate design, 439fl ax fi bres, 17, 429fl exible fi bre material, 291fl exural cracks, 100fl exural strengthening

applications, 94–5with strips in cement factory, 95with strips of solid slap fl oor, 95

design, 95–100debonding at fl exural cracks, 100debonding at shear cracks or

discontinuities, 98–100determining shear stress between

EBFR and concrete surfaces, 99EBFR debonding failure modes, 96pull-off test and corresponding strain

and shear stress, 97strip end debonding failure, 96–8

shear strengtheningnew holes in beam in a building, 101with strips and fabrics in cement

factory, 102fl uorinated polymers, 180fl uoropolymer-coated glass fabric, 39fl uoropolymer coatings, 59fl uoropolymer fabrics, 57–8FMF see Freiburger

Materialforschungszentrumfoils, 34–5

see also polymer foilsforce-density method, 235FOS see fi bre optic sensorsfree-space optical porting techniques, 341Freiburger Materialforschungszentrum, 320FTL Design Engineering Studio, 253functional canals, 299Futuro houses, 8, 441

Gaussian curvature, 191gel spinning, 23Georgia Institute of Technology, 356

German Antarctic Polar Research Station Neumeyer III, 436

German Bionics-Competence Network Biokon, 312

Gerontology Technology Centre, 387–8, 389GFRP see glass fi bre reinforced polymersgiant reed see Arundo donaxglass, 211glass-fi bre carrier fabric, 284glass fi bre reinforced polymers, 442–3, 451

casing, 457reinforcement in Wotton bridge deck, 117seismic retrofi tting, 113

glass fi bres, 28, 73, 130, 180, 377, 427Gore Tenara, 53, 58, 240Gore-Tex, 57gradient textile technology, 291, 301graphite fi bres, 75GSW Building, 391

Haitian earthquake, 436hand laminating process, 432Hawthorn campus, 384HEA 240 steel girders, 270heat-hardening prepregs, 433hemp fi bres, 17, 429Herzog de Meuron’s Elbe Philharmonic

Concert Hall, 8high stretch PET foils, 34high-tech textiles, 4–5Hightex GmbH, 356honeycomb, 429Hooke’s law, 214Hopkins Architects, 244horizontal bracing, 271horsetail see Equisetum hyemaleHostafl on, 57Hubert H. Humprey Metrodome, 261

Ibach bridge, 71IEA see International Energy AgencyIIP see internal infl ation processindium oxide, 185infl ated membranes, 247Institute of Lightweight Construction, 317Institute of Textile Technology and Process

Engineering in Denkendorf, 33, 294, 314, 318

insulation systemstextiles to control thermal losses and

solar gains, 351–74fl exible translucent thermal insulation,

352–8fully membrane-integrated

photovoltaics, 364–73selective and low-E functional coatings

for membrane materials, 358–64intensity sensors, 335–6interferometry, 336

478 Index


internal infl ation process, 435, 449internal steel stirrups, 103, 104International Energy Agency, 364ISIS-Canada, 115ISO 1421, 138, 139, 142, 143, 144, 146, 147,

148ISO 105-A2, 174ISO 105-A05, 174ISO/TC92/SC1, 174ITV solar textile, 33Izmir earthquake, 436

Jasmax, 382

Kevlar, 53, 59, 75–6, 333, 427key technology, 219knitted fabric, 31

Labor Blum biaxial machine, 135Laboratorium Blum, 274laminar composite, 429LBV P1106, 150LBV P1111, 140LCP see liquid crystal polymerslife-cycle costing, 378, 411, 416light, 359light exposure tests, 173–4light transmission, 154–5, 185lightweight constructions, 49, 66–7, 420

materials, 420technical plant system, 290–308

applications, 304–7biomimetics to enhance the lightweight

potential of composites, 291–5exploiting plant role models for

technical use, 295–301future trends, 307–8production, 302–3

lightweight fi bre reinforced plastics, 290Likert scale, 406limit state design, 119linen weaving, 53liquid crystal polymers, 27load and resistance factor design, 119Lotosan, 312Lotus-effect, 47low-emission coatings, 38low emissivity, 360low-molecular-weight gas ethylene, 208LRFD see load and resistance factor designLSD see limit state designluminaria, 249

Mach-Zender interferometer, 336man-made fi bres, 17Marsyas, 249Masdar Plaza, 2Masonry Strengthening with Composite

Materials, 114

masonry structures, 111–14maximal anchorage force, 97–8mean radiant temperature, 380melamine fi bres, 28melt spinning, 22melt-spun fi bres, 17membrane construction, 49membranes, 14

see also textile membranesMichelson system, 337microbending sensors, 335microfi bre coatings, 32Millennium Dome see O2 Arenamodern biomimetics, 294modifi er, 209mould heating process, 435multi-mode fi bres, 334

nanofi bre coatings, 32Nanogel, 253nanotechnology, 41, 45, 47nanotubes, 121–2narrow textiles, 30NASA Ultra Long Duration Balloon, 14National Aeronautics and Space

Administration, 422National Aquatic Centre, 416natural fi bres, 19, 51near surface mounted reinforcement, 93–4net-like fabrics, 50, 61–2Nomex, 431non-modifi ed thermoplastic ETFE-

foil, 208nonwovens, 30–2Nowofl on ET 6235, 207NSMR see near surface mounted

reinforcementnylon, 51

O2 Arena, 244OF see optical fi bresOMNIUM housing project, 441optical fi bres, 333–4optical spectrum analyser, 337optical time-domain refl ectometer, 345OSA see optical spectrum analyserOTDR see optical time-domain

refl ectometer

pacesetter technology, 219panama weaving, 53PBI see polybenzimidazolePBO see poly-p-phenylene-

2,6-benzobisoxazolePCMs see phase changing materialsPCV-coated aramid fabric, 40PD Interglas Atex, 61PEEK see polyether ether ketonePES see polyester

Index 479


PET see polyethylene terephthalatepetrochemical processes, 208phase changing materials, 4phenol resins, 425, 438photocatalytic membranes, 253photovoltaic facades, 5physical vapour disposition, 46piezoelectric wafer active sensors, 332plain weaving, 53Planck’s law, 162PlanktonTech, 322, 325Plant Biomechanics Group Freiburg, 312,

314, 318, 320plastic optical fi bre, 347plastics, 207

classifi cation, 207defi ned, 205–6morphological structure and solubility,

208poly-p-phenylene-2,6-benzobisoxazole, 27polyamide, 27, 429polybenzimidazole, 27polycarbonate, 35, 211polyester, 51

fabrics, 56–7resins, 77, 424, 431

polyether ether ketone, 27, 78polyetherimide, 27polyethylene, 4polyethylene terephthalate, 27, 56, 130Polyfunctional Technical Textiles

Against Natural Hazards, 346polyimide, 27, 342POLYMAR, 61polymer coating, 46–7polymer fi bres

structural health monitoring, 330–49concept, 330–2future trends, 344–6smart composites, 340–4smart fi bres, 333–40smart textile, 346–9

polymer foilsbuilding-physics characteristics,

211–12fi re behaviour, 211noise and heat insulation, 212radiation transmission, 211–12

construction methods, 190–2anticlastic and synclastic distribution,

191corner region with the counter-

curvature, 191ETFE-foil cushion with predominantly

synclastic curvature, 190ETFE-foil structure with anticlastic

curvature, 190mechanically prestressed systems, 190pneumatically prestressed systems, 191

construction types, 192integrated sun protection elements, 193pneumatic ETFE-foil cushions types,

192development potential, 219–20future requirements for architecture and

civil engineering, 220–3single-layer ETFE-foil cupola, 222

historical development, 193–2021996 Airtecture, Esslingen, 1952005 Allianz Arena, Munich, 199, 2002005 Atrium Roof IABG, Ottobrunn,

200–12005 AWD-Arena, Hanover, 199–2002002 Conference Building, Deutsche

Bundesstiftung für Umwelt, Osnabrück, 198–9

2000 Cycle Bowl, Expo Hanover, 195–62004 ETFE-foil umbrellas, Industrie-

und Handelskammer, Würzburg, 1992001 Garden of Eden, St. Austell,

Cornwall, 196–72001 Information Centre, Walchensee

Power Station, Kochel am See, 1971994 Lion House, Hellabrunn Zoo,

Munich, 1941982 Mangrove Hall, ‘Burgers’ Zoo,’

Arnhem, 1932002 Masoala Rainforest, Zurich Zoo,

197–81996 Moveable ETFE-foil cushion,

Olympic Park, Munich, 194–52008 National Swimming Centre and

Olympic Stadium, Beijing, 201–21999 Thermal Baths, Prien, Lake

Chiemsee, 1952005 Tropical Island, Brand, 201National Swimming Centre, Beijing,

202Olympic Stadium, Beijing, 203

load-bearing behaviour, 215–19factors of infl uence, 215loading behaviour under snow load,

218principal load-bearing behaviour,

215–16realisable spans, 218–19snow loads, 218square ETFE-foil cushion, 216two-layer cushion under wind suction,

217under wind and snow loads, 216–18wind suction loads, 216–18

material properties, 210–15deformation behaviour and stress–

strain curve, 214–15eco-balance and recyclability, 213–14mechanical properties, 214–15uniaxial stress–strain curve, 215

480 Index


morphology, 206–7amorphous and semi-crystalline

compositions, 207macromolecules basic confi gurations,

207macromolecules confi guration and

composition, 206–7morphology and production progress,

205–10monomers units, 208–9monomers units structural formulae,

208plastics and ETFE development, 205–6

defi ned, 205–6morphological structure and solubility,

208plastic classifi cation, 207plastic pyramid, 206

production process, 209–10copolymerisation, 209drying and granulation, 209extrusion, 209–10successive production steps, 210

structural–chemical characteristicsanti-adhesive characteristic, 213durability, 213

typology, basic shapes and application range, 203–5

basic boundary geometries, 204ground plan geometries and type of

construction, 204project location according to countries

and continents, 204structural elements utilisation and

application, 205used in construction, 189–226

polymers, 205polyphenylene sulphide, 27, 78polysulphone, 78–9polytetrafl uoroethylene, 36–7, 131, 240, 266,

351, 377challenges in using in architecture,

398–418fabric, 40fi bres, 130foils, 407–9PTFE-coated fi breglass fabric, 409terpolymer, 34, 37vs double-glazed facade material

properties, 409–12vs ETFE and double-glazed facades

energy-effi ciency attributes, 401–4polyurethane, 37polyvinyl chloride, 34, 130, 131, 438polyvinyl chloride coating, 36polyvinylfl uoride, 36ponding, 235pool research, 312–13, 316–18, 321Power Plastic, 253

PPS see polyphenylene sulphideprefabricated strips, 93–4prepreg process, 432–4prestressing technology, 122–3PTFE see polytetrafl uoroethylenePTFE-coated glass fabric, 39, 40, 240PTFE-coated glass fi bre fabrics, 131PTFE-coated high tensile PTFE fabric, 39pultrusion process, 82, 302, 306

machine devices, 83PUR see polyurethanePUR-coated light polyester fabric, 40PVC see polyvinyl chloridePVC-coated polyester, 240PVC-coated polyester fabric, 39, 55, 131,

171PVC coatings, 55, 58–9PVC foil, 34PWAS see piezoelectric wafer active sensors

quantum optics, 334

radiation, 161numerical calculation, 161–71

balance of a parallel two-layer system, 165–8

Boltzmann laws, 161–2emissivity and absorption for non-black

bodies, 163–4layer temperatures, 169–71Planck’s law, 162total radiation balance, 168–9transmission through an interface with

decreasing thickness, 164–5thermal transfer, 157–8

Raman scattering, 346ray optics, 333Rayleigh backscattering component, 346R&D coatings, 45–7

metallisation and layers with ceramics, 46

polymer coating by atmospheric plasma, 46–7

sol-gel techniques, 45–6R&D fi bres, 41, 45

FEM calculation, 45nanotechnology, 41, 45

recyclability, 378reinforcing fi bres, 425–9resin transfer moulding technique, 291reverse biomimetics, 311RMIT see Royal Melbourne Institute

of TechnologyRoving 870, 445Royal Melbourne Institute of Technology,

391proposed design, 391proposed solar chimney, 393solar chimney functionality, 392

Index 481


S-glass, 73, 75sandfi sh see Scincus scincussandwich composite, 429sandwich construction, 7Sauerbruch Hutton Architects, 390scalar waves theory, 333Scincus scincus, 321screens, 2sensor, 334serviceability limit state

verifi cation in EBFR, 100–1verifi cation in EBSR, 106

shear behaviour, 151, 152shear resistance, 103, 106shear stiffness, 132, 153sheeting, 5SIA166, 99, 100, 105, 110SIA262, 99, 103Sika CarboShear L, 106silica aerogels, 354–5silicone, 37, 240silicone-coated glass fabrics, 39, 244, 250silicone-coated glass fi bre fabric, 171silicone coatings, 60–1silicone rubbers, 131silk, 25silver, 26single-mode OF, 334SKO see Soft Kill OptionSLS see serviceability limit statesmart materials, 47smart textiles

characterisation and standardisation, 349manufacture, 347product types and their applications,

347–9structural health monitoring, 330–49

concept, 330–2future trends, 344–6smart composites, 340–4smart fi bres, 333–40

Snell’s law, 333soap fi lms, 234Soft Kill Option, 324sol-gel technology, 45–6solar radiation, 158, 359solar spectrum, 359SolarNext AG, 356Space House, 422, 436Space Offi ce, 422, 436–42

design, 439–42fl oor plan, 440sections, 440

materials, 436, 438–9Neumayer III station, 437wall concept, 438

spacer fabrics, 32–3spinning technology, 434split fi bre technology, 32

spray-tester, 178spun glass fi bres, 269Sputnik I, 421stainless steel, 28Stokes component, 346stress concentration factor, 139–40strip test, 137structural health monitoring

concept, 330–2damage detection, 332load monitoring, 331–2

fi bre optic sensors types, 334–8FBG basic principle, 338fi bre optic system, 335intensity sensors, 335–6interferometer sensor power

output, 337Mach-Zender interferometer, 336microbending sensor, 335phase modulation or interferometers,

336–7sensor based on wavelength or Bragg

gratings, 337–8future trends, 344–6

distributed sensing systems, 345–6highly multiplexed systems, 344–5

smart composites, 340–4FBG response to transverse stresses,

343–4FBG response to uniaxial tension,

342–3microbending and other issues for

embedded sensors, 341–2peak distortion by strain gradients, 343peak drifting under uniaxial strain, 342peak splitting by transverse

stresses, 344smart patch composite, 341

smart fi bres, 333–40FBG interrogation systems,

characteristics and performance, 339–40

fi bre Bragg grating response to strain and temperature, 338–9

optical fi bres nature and principles, 333–4

wavelength drifting, 339smart textile, 346–9

characterisation and standardisation, 349

manufacture, 347product types and their applications,

347–9sensor-embedded textiles, 348

smart textile and polymer fi bres, 330–49

sustainable buildingsBaader Wertpapierhandelsbank

textile lamellars opening, 388

482 Index


biomimicry, 381–95cactus fl eshy ribs shading effect, 382simplifi ed penguin feather, 387ventilation principle in burrow of

black-tailed prairie dog, 389major obstacles, 377–9

cost, 378daylight and shading, 378embodied energy, 378life-cycle costing, 378other obstacles, 378recyclability, 378U-value, 378ventilation, 378

operational energy demand reduction strategies, 379–81

avenues to alter light transmission, 381–6

simplifi ed ventilation principle, 390textile and biomimicry contributions

to infl uence natural ventilation, 389–92

textile materials contributions, 381–92textile wing on GSW Building

rooftop, 391variable thermal performance

improvements, 386–8RMIT

proposed design, 391proposed solar chimney, 393solar chimney functionality, 392

Swinburne Universityair-intake element, 385ETFE roof construction, 385overlaying graphics on three-layer

ETFE cushion, 386Sylvia Park Offi ces

architectural design, 383detail of textile shading system, 384honeycomb semitransparent tension

membrane fabric sunshade, 383textile applications, 375–95

area of improvements with regard to mitigation of climate change, 376

deliberations on future applications, 392–5

Gerontology Centre, 389materials implementation in

Australia, 377–9textile materials, 258–87

applications and properties used in roofi ng and facades, 260–87

future trends, 287role, 259–60

Swinburne Universityair-intake element, 385ETFE roof construction, 385overlaying graphics on three-layer

ETFE cushion, 386

Sylvia Park Offi ces, 382architectural design, 383detail of textile shading system, 384honeycomb semitransparent tension

membrane fabric sunshade, 383synthetic fi bres, 19, 51–2synthetic rubber, 38

tailored fi bre placement, 291tape overlay process, 434TDM see time division multiplexingtechnical biology, 311technical plant stem, 312, 318–19technical plant system

applications, 304–7lightweight load carrying roof

substructure, 306telescope stiff and lightweight

substructure, 307biomimetics to enhance the

lightweight potential of composites, 291–5

dragonfl y thorax, 293robotic arm model after cactus

wood, 293bionic abstraction

giant reed properties and transfer into techniques, 300

horsetail properties and transfer into techniques, 299

wood properties and transfer into techniques, 297

exploiting plant role models for technical use, 295–301

Arundo donax bending test, 301combining different role models

principles, 301composites increasing bending

stiffness using foam core, 299double ring structure with connecting

beams, 299giant reed, 300–1giant reed stem cross-section, 296horsetail, 297–9horsetail stem cross-section, 296spruce compression wood, 297T-struts in horsetail stem

periphery, 298wood, 295–7

FEM modelling, 302future trends, 307–8lightweight constructions, 290–308

robot arm, 292tailored fi bre placement, 292

production, 302–3braid-pultruded technical plant

stem, 306braid-pultruded tubular profi le, 304braiding technique, 304

Index 483


detail of ITV braid-pultrusion technology, 303

hand impregnated technical plant stem, 305

ITV braid-pultrusion technology, 303technical plant stem with polyurethane

foam matrix, 305Tefl on, 57, 240Tefl on foil laminate, 284Tefzel, 206tempering, 435–6Tensairity, 248, 312, 320tensile fabric roof, 253tensile textile structure

applications, 244–52architecture, 244–8

Georgia Dome, 246glazed roof lights, 245infl ated cushion at the Bull Ring, 248Millennium Dome, 246waveform at Denver airport, 247

architecture and design, 229–54fabric architecture concept, 231history and development, 230tensile membrane structure of the open

covering type, 231art and design, 248–52

acoustic and light refl ectors/diffusers, 250–2

exhibition stands, 249–50high-level fabric diffuser, 251low-level diffuser/refl ectors, 252luminaria sculptural interior, 250tensile fabric sculpture, 249TensiNet competition exhibition stand,

251assembly and construction details, 237–9

corners, 239edge details, 238–9point supports, 239rainwater discharge funnel, 240rainwater run-off, 239safety, 239

common materials and architectural properties, 240–4

acoustics, 243fi re resistance, 243–4light, 241–2material types, 240–1thermal performance, 242–3welded seams pattern, 243

design development, 233–9boundary cable, 238form-fi nding, 234–5patterned panels, 236patterning and assembly, 236–7pretension, 237scale model, 235

future trends, 252–4

general principles, 231–3anticlastic surfaces, 234spider’s web loaded with dew, 232

tension failure, 116tension force-loaded machine elements, 294Tensotherm, 253Terminal EF, 270–87

building thermal simulation, 284calculated simulations, 284connection bridge, 285

between parts of the building, 272construction of the covering, 284membrane static calculation, 286–7showing elliptical steel beams, 285with translucent fabric, 285

daylight system overview, 282details connecting the textile membrane

to steel beams, 280energy concept, 283–4fi re resistance, 276–7glass-fi bre insulation material, 275–6inner membrane, 275intelligent fl exible facade with different

behaviours in summer and winter, 281–2

membrane facadefunctionality, 278–81internal view, 272layers and installation, 273membrane characteristics overview, 276

natural ventilation system overview, 281north-west side, 270other edges in Keder profi les, 286overall concept purpose, 283overview, 270–1physical behaviour and material

properties, 273–4physical product assessment, 277specifi c challenges, 271tests and assumptions, 274theoretical calculations and load bearings,

272–3thermal behaviour simulations, Plate Vthermal system, 278–9

thermal building masses activation, 283Young’s modulus, 274–5

tetrafl uoroethylene-hexafl uoropropylene-vinylidenefl uoride copolymer foil, 34

textile architecture, 259Textile Climate, 170, 171textile materials

applications and properties used in roofi ng and facades, 260–87

early examples and principles, 260–8Degrees North by Kenzo Tange, 261Dome over Manhattan, 262event arena roofi ng system details, 267event arena side view, 266

484 Index


external view of city in the Antarctic, 260

internal view of city in the Antarctic, 261

international design competition, 268M&G research laboratory, 264Munich Ice Arena, 265Munich Swimming Centre, 265unbuilt event arena, 264US pavilion aerial view, 263US pavilion Cable Dome, 262US pavilion internal view, 263

future trends, 287materials and light transmission, 268–9

combined construction thermophysical characteristics, 269

glass fi bre insulation material, 270multi-layer construction elements, 269

role, properties and applications in sustainable buildings, 258–87

sustainable buildingsrole, 259–60

Terminal EF, 270–87textile membranes, 243

chemical, light and fi re durability, 172–6comprehensive environmental

simulation, 172–3EN ISO 1182 test for non-

combustibility, 176environmental simulation set-up, 173fi re tests, 174–6increasing sensibility to degradation,

172light exposure tests, 173–4standards for fi re resistance, 175wicking tests, 174

commonly used standards, 179standards for membrane materials,

182–4developing and testing for tensioned

structures, 129–85authorisation, 132–4test methods and characterisation,

132–4fl exible translucent thermal insulation,

352–8aerogel/ETFE exterior view, 357aerogel/ETFE interior view, 358aerogel fi lling in pneumatic structures,

355aerogel fl eece/wrap, 355–6employing aerogel cushions, 356–8fi brous formation aerogel, 356granular silica aerogel, 354insulation values, 354roof section through the aerogel/ETFE

cushion, 357silica aerogels properties and utilisation

principles, 354–5

fully membrane-integrated photovoltaics, 364–73

ETFE embedded a-Si PV, 368ETFE-embedded PV modules, 367ETFE-photovoltaic scope and

PTFE-photovoltaic application, 365–6

fl exible a-Si PV, 367Mercedes Benz Arena with PV

fl exibles, 371modules attached to coated translucent

fabric material, 369photovoltaic output forecast, 372–3photovoltaic technology and

application principles, 366–71photovoltaic tensile structure, 365photovoltaics in foil and membrane

structures application, 364–5PV fl exibles exterior view, 372PV fl exibles integrated in pneumatic

constructions, 369PV fl exibles interior view, 372small four-point sail with PTFE/glass

membrane, 370transmission view against the light, 370

future trends, 179–81, 185improving mechanical, physical and

optical properties, 181, 185improving mechanical and chemical

durability, 179–80improving weight, 185light transmission and refl exion, 185thermal insulation, 181, 185

heat and energy transport, 155–71blackbody radiators energy curves, 163constant temperature, Plate IIfurniture store outside view, 156heating and thermal emission, 158measured material temperatures

at the end of April, 156radiation numerical calculation,

161–71secondary radiation based on layer 1,

168secondary radiation based on

layer 2, 167solar radiation envelope, 163thermal transmission, 156–61transport mechanisms, 161

light transmission, 154–5degree of transmission and refl exion,

155solar functions of textiles in

construction, 154material strength determination, 136–42

long-term strength behaviour, 141–2short-term strength behaviour,

136–41strip test, 137

Index 485


material systems, 129–32coating materials, 130–1composites coated textiles, 131–2fi bres and fabrics, 130

mechanical tests and behaviour, 134–42biaxial machine, 134–5Labor Blum biaxial machine, 135mechanical strength and structural

stability, 135–6radiation intensities

passage of an approaching radiation of +00, 166

passage of an approaching radiation of −00, 166

reduce thermal losses and control solar gains, 351–74

cushion energy-related aspects and physics, 353

options to improve membrane building envelope performances, 373

selective and low-E functional coatings for membrane materials, 358–64

Bangkok Airport’s energy concept, 362

Bangkok Airport’s interior, 362Dolce Vita Tejo shopping mall, 364low-E coating on ETFE foils, 363–4low-E coating on PTFE/glass fabrics,

361–2low-E surfaces physical principle, 360opaque low-E coating, 363temperature stratifi cation, 361transparent selective coatings physical

principle, 358–9transparent selective low-E

coating, 363strength of connecting systems, 142–53

cable edge test, 149characteristic load history, 151clamped connections, 145–8clamped edge test detail, 147deformation behaviour, 149–53elastic moduli evaluation, 152seam test failure, 143shear behaviour determination, 152tubular and cable edges, 148–9uniaxial test proposal for shear

stiffness estimation, 153welded seams long-term behaviour,

144–5welded seams short-term behaviour,

142–4surface cleaning properties, 177–8

grey-scale for assessment, 178PTFE-coated samples, 180PVC-coated samples, 179revolving drum, 177silicone-coated samples, 181spray-tester, 178

temperature distributionconstant temperature, Plate IIunder a clear sky at night, Plate IVunder solar radiation in a clear sky,

Plate IIIunder solar radiation with 70%

aligned and 30% diffuse radiation, Plate I

thermal transport, 158massive building element, 159membrane seal, 159

transmission, refl ection and absorption spectra

PVC-coated polyester fabric, 171silicone-coated glass fi bre fabric, 171

textiles, 259applications in sustainable buildings,

375–95biomimicry, 381–92deliberations on future applications,

392–5facades operational energy demand

reduction strategies, 379–81implementation in Australia,

377–9textile materials contributions to

operational energy demand reduction, 381–92

buildtech composite materials formation, 38–40

ETFE foil, 41membrane properties, 42–4PTFE-coated glass fabric with 10%

translucency, 40challenges in using in architecture,

398–418aim, objectives and methodology,

399–400future developments, 417–18results of interview, 400–16summary of results, 416–17

fabric technical characteristics and requirements for modern structural engineering, 62–6

draft, design, computation, engineering success, 65–6

thermal and acoustic behaviour, 63–5

formation technology, 29–34braided fabric, 31fl at knitting, weft knitting and warp

knitting, 30ITV solar textile, 33knitted fabric, 31narrow textiles, 30nonwovens, 30–2post-treatment of textiles, 33–4spacer fabrics, 32–3woven fabrics, 29–30

486 Index


historical development of fabrics used for construction, 50–3

artifi cial fi bres world production, 52atlas/satin/twill weaving, 54basket/panama weaving, 54fabric elements composition, 52–3fabrics from natural fi bres, 51fabrics from synthetic fi bres, 51–2plain/canvas/linen/tabby weaving, 53

materials currently used in construction, 55–62

coated fabrics, coatings and topcoats, 58–61

fl uoropolymer foil with glass-fi bre reinforced net, 62

low-wick prepared weaving, 55net-like fabrics, 61–2polyester base fabric, 56PTFE-coated fi breglass membrane, 60PVC-coated polyester fabric with

topcoat, 59PVC-laminated PES mesh fabric, 61selected fabrics and foils technical

characteristics, 60silicone-coated fi breglass membrane, 61uncoated fabrics, 56–8

role in providing biomimetic solutions for construction, 310–26

biomimetics, bionics and technical biology defi nitions, 311–12

biomimetics applications in architecture, 318–21

future trends, 321–6methodology in architecture and

engineering, 312–18natural development benefi ts for

technical purposes, 312technical characteristics and requirements

for building and construction, 49–67

future trends, 66–7types and production used for building

and construction, 13–47changing fi bre properties by post-

treatment and fi nishing, 23–6coatings, 35–8FEM calculation, 45fi bre characteristics and properties,

17–22fi bre materials for buildtech

applications, 26–9fi bre production, 22–3fi bres, 15–16foils, 34–5future trends, 41, 45–7nanotechnology, 47primary structures, 40–1R&D coatings, 45–7R&D fi bres, 41, 45

smart materials, 47top coats, 38

thermal transmission, 156–61basic physics

convection, 157radiation, 157–8thermal conduction, 157transport phenomena in building

industry, 158–61thermofi xation, 33thermoplastic resins, 78thermoplastics, 76, 424thermoset, 424thermoset pultrusion, 302thermosetting resins, 76three-axis CNC-milling, 447THV-coated ETFE, 40THV-coated PTFE, 40TIMax GL, 269time division multiplexing, 344–5titanium dioxide, 26, 185TMF see transfer matrix formalismtoldos, 230top-down approach, 314–15topcoats, 38, 58–61Tournesol, 7, 8Tournesols, 422TR55 2000, 89, 91TR55 2004, 99, 100Trabant car, 429transfer matrix formalism, 343transparent selective coatings, 359tubular rods, 304Twaron, 427twin-axis tests, 149

U-value, 378, 386, 411–12ultimate limit state

verifi cation in EBSR, 104–6anchorage pullout of CFRP L-shaped

strips, 106opening of the overlapping of L-shaped

strips, 106peeling-off and CFRP plate

fracture, 106ultrahigh molecular weight

polyethylene, 28–9ultraviolet radiation, 88, 212UV-A, 211UV-B, 211, 212UV-C, 211, 212

vacuum bagging, 291vacuum infusion process, 435vacuum insulation panels, 352Valmex vivax, 59, 62, 252velaria, 230ventilation, 378Venturi effect, 390

Index 487


Vercelli castle, 112, 113vinyl-coated fi breglass fabric, 261vinyl esters, 77–8vinylidene fl uoride terpolymer, 37VIP see vacuum insulation panels

Walbrook, 8, 442–60composite components production and

assembly, 447–60aluminium profi le at rear of the trunk

for transferring loads, 455assembled parts, ready for delivery

and installation, 459coating system tests, part 1, 458coating system tests, part 2, 4583D-CAD planning of transfer part at

specifi ed trunk, 454endplate model, 448endplates attachment sequence, 452endplates for the ribs, 449facade elements ready for

delivery, 460fi nished mould, 448GFRP casing, 457laminate concept for ribs, 457positive models, 448process advantages, 449–50production scheme, 447production sequences according to

IIP, 451rib element in the form, 453rib gaps, 453rib production test stages, 450ribs of types 200 and 500 mm, 453steel profi les and rib in mock-up, 457transfer part at specifi ed trunk, 454trunk before lacquering and in

fi nished state, 458trunk construction process, 452trunk technical drawing, 456

visual mock-up, 459wind and weathering stability tests, 460

cross-section, 444fi nal street view, 461materials, 444–6

matt/tissues used in laminate, 444rib type 350, 446specifi cations, 445types of laminate used, 444

street view, 443view, 442

warp knitting, 30water jet technology, 447Watercube, 202, 247wavelength division multiplexing, 345weft knitting, 30welded seams

long-term behaviour, 144–5behaviour according to load, 144–5strength reduction after exposure to

weather, 145short-term behaviour, 142–4

biaxial seam strength/bursting test, 144seam strengths in uniaxial tests parallel

to threads, 142–4wet application, 92wet lay-up, 82wet spinning, 22wicking tests, 174wood–polymer composite materials, 425wool fi bres, 17Wotton Bridge, 116–17

completed bridge, 117GFRP and CFRP reinforcement in bridge

deck, 117woven fabrics, 29–30

xenon arc fading lamp test, 173

Young’s modulus, 274–5, 301