A6.3 A BRIEF HISTORY OF PNEUMATIC STRUCTURES Introduction: In the field of human constructions, pneumatic structures are fairly recent, since they did not appear concretely until the second half of the twentieth century. While it is difficult for them to directly compete with structures made of more conventional building materials, such as stone, concrete or wood, their specific properties make them excellent candidates for a wide variety of temporary or permanent applications. They remain unique for example in the possibility of covering large areas, being particularly effective for roofing for example. The idea of using air as a tool to support a load is old, but it is necessary to have a reliable technology for the sustainable implementation, whether in the field of textile materials used, links between different pieces of fabric, methods and means of construction as well as means of pressurization. Current achievements highlight the maturity of manufacturing processes. Moreover, the evolution of theoretical knowledge in the different domains (materials, loadings, behavior) as well as in the methods and means of modeling today makes it possible to justify their sizing in a more and more reliable way. It is hoped that recent technical developments (developments of ETFE cushions, tensairity) will be followed by other innovations in the field, so that pneumatic structures are naturally part of the modern architectural environment. This section provides a brief history of major developments in pneumatic construction structures as well as recent developments. We do not refer in this section to non-structural applications. 1. The first steps In 1893, J. A. Sumovki was one of the first to conceptualize the idea of using a gaseous fluid to stiffen flexible elements. Its patent "Tubular structure filled with gaseous fluid" presents combinations of basic elements, pressurized with a gas, and concepts of assembling these elements forming supporting structures, such as the principles of bridges ( figure 1). It is probably the first concepts of inflated structures (air-inflated). The beginnings of mono-membrane structures intended to cover large areas are generally attributed to the engineer English F. W. Lanchester, who filed two patents relating to pneumatic structures. The first one is titled "Construction of tentes for field hospitals, depots, and loke purpose. It describes the principle of a tent type mono-diaphragm, shaped and maintained by the air pressure, large surface current, without supports. The second patent concerns the 'Construction and roofing of building for exhibitions and like purposes'. It describes principles of flexible roofs maintained by pressure, anchored on masonry or concrete structures, temporary or semi-temporary. The basic principles are already described in these patents, such as the shapes to be cut to obtain the required shapes, the connections between the fabrics, the materials, the tensions in the membranes calculated by the engineers, the anchors by lacing, the air locks, and how to erect them. Figure 1: arched shape bridge
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A6.3 A BRIEF HISTORY OF PNEUMATIC STRUCTURES Introduction: In the fieldofhumanconstructions,pneumaticstructuresare fairlyrecent,sincetheydidnotappearconcretelyuntilthesecondhalfofthetwentiethcentury.Whileitisdifficultfor them to directly compete with structures made of more conventional building materials,suchasstone,concreteorwood,theirspecificpropertiesmakethemexcellentcandidatesforawidevarietyof temporaryorpermanent applications.They remainunique for example in thepossibilityofcoveringlargeareas,beingparticularlyeffectiveforroofingforexample.The idea of using air as a tool to support a load is old, but it is necessary to have a reliabletechnology for the sustainable implementation, whether in the field of textilematerials used,linksbetweendifferentpiecesoffabric,methodsandmeansofconstructionaswellasmeansofpressurization. Current achievements highlight the maturity of manufacturing processes.Moreover,theevolutionoftheoreticalknowledgeinthedifferentdomains(materials,loadings,behavior) aswell as in themethodsandmeansofmodeling todaymakes itpossible to justifytheir sizing in amore andmore reliableway. It is hoped that recent technical developments(developmentsofETFEcushions,tensairity)willbefollowedbyotherinnovationsinthefield,sothatpneumaticstructuresarenaturallypartofthemodernarchitecturalenvironment.This section provides a brief history of major developments in pneumatic constructionstructures as well as recent developments. We do not refer in this section to non-structuralapplications. 1. Thefirststeps In 1893, J. A. Sumovki was one of thefirsttoconceptualizetheideaofusingagaseous fluid to stiffen flexibleelements. Its patent "Tubular structurefilled with gaseous fluid" presentscombinations of basic elements,pressurizedwithagas,andconceptsofassembling these elements formingsupporting structures, such as theprinciples of bridges ( figure 1). It isprobablythefirstconceptsofinflatedstructures(air-inflated).The beginnings of mono-membrane structures intended to cover large areas are generallyattributedtotheengineerEnglishF.W.Lanchester,whofiledtwopatentsrelatingtopneumaticstructures. The first one is titled "Construction of tentes for field hospitals, depots, and lokepurpose. Itdescribes theprincipleof a tent typemono-diaphragm, shapedandmaintainedbythe air pressure, large surface current, without supports. The second patent concerns the'Constructionandroofingofbuildingforexhibitionsandlikepurposes'.Itdescribesprinciplesofflexibleroofsmaintainedbypressure,anchoredonmasonryorconcretestructures,temporaryor semi-temporary. The basic principles are already described in these patents, such as theshapes to be cut to obtain the required shapes, the connections between the fabrics, thematerials,thetensionsinthemembranescalculatedbytheengineers,theanchorsbylacing,theairlocks,andhowtoerectthem.
Figure1:archedshapebridge
If the principles of pneumatic structures were laid inthose years, they were not manufactured for twomainreasons:thelackofappropriatematerials,aswellasthelackofmarketinthefield.The invention of nylon (1938)marks a turningpoint intheevolutionofinflatablestructures,becauseitprovidesafirstmaterialfortheconcreterealizationofstructures.The first structures that can be described as inflatablebuildings were built for the US military to protectAmerican radars subjected to severe environments,mainly in cold areas, close to Alaska. These structureswereofcoursenottointerferewithradarsignals.WalterBird was the leader of the Cornell Aeronautical Laboratory working group that studied andimplementedthesefirststructurescalled"radome"in1948.2. Pneumaticstructuresincivilsociety
In1956WalterBirdlefthispositionattheCornellAeronauticalLaboratoryandcreatedBirdairforthedevelopmentofradarprotectionstructures.Birdairdevelopedtheconceptandexpandedittoincludevariousprotectivestructuresformedium-sizedroofs,includingstorageandsportsfacility protections. The curvature of the time magazine magazine offered him an importantshowcase at a key moment in the development of inflatable structures: the 60s. The rise ofcompanies suchasBirdair allowed the constructionof various inflatable shelters,highlightingtheadvantagesofthistypeofbuildings.Examplesofconstructionshelters,exhibitionbuildings,icehockeyenclosures,militarystructures,andeventravelingchurchescaneasilybefound.One of the precursors in textile structures in Europewas Frei Otto. Among his important work ontensionned struutcures, he devoted the years 1959 to1961mainlytothestudyofpneumaticstructures,andpublished his work in 1962, including the variouspossibleforms,combiningdifferentconfigurations,andusingcablesorwirenetstoimposespecificgeometries.Figure7 showsan exampleof twoassociated spheresforming the building of the High-Voltage TestLaboratoryinCologne.Thisperiodwasalsoconducivetovisionariesseeinginthisnewtechnologythepotentialtocreatenewspacesfor living, fully utilizing the potential of membranestructures stretched to cover very large spaces. Forexample, Q. w. Newmark proposed in 1962 largeinflableroofsforcoveringwidespaces(figure8).Someiconic concepts include the Pneumatic Dome forManhattan in 1950, designed by Buckminster Fuller(Figure8), andTheArcticCity of FreiOtto andEwaldBubner(Figure9). In thisverysuccessfulperiod inprojectsagroupof3students inarchitectureat theschooloffineartsinParisembarkedonthepathofutopianstructures,andformedthegroupAerolande.Theirstudentprojectisapneumaticarchitecturecomprisingthreeparts:theDyodon.Itwasan
experimental dwelling consisting of envelope mattresses (Jean Paul Jungmann), an inflatabletubeshallarrangedaccordingtothegeodesicdistributionofadodecahedron(JeanAubert)andan exhibition hall consisting of two domes in overpressure supporting a stretched canvas(Antoine Stinco) They also designed inflatable and playful furniture. They formed with thesociologistsJeanBaudrillardandHubertTonka,aswellasotherstheUtopiegroup,until1976.Oneoftheobjectivesofthisgroupwastodesignamobilearchitecture,ephemeralanddynamic,goingagainstclassicalstaticarchitecture.
2.2. Osaka1970exposure:onpneumaticstructuresThe World Expo in Osaka in 1970 was a particularly important showcase for pneumaticstructures.Severalpneumaticpavilionswerepresented,illustratingsomeofthevariousshapesthat can be obtained: inflated beam assemblies, inflatable roof, depressurized structure,aircushions.
The floating theater (Figure11) is oneof the fewexamples of depressurized structure. It is ahybrid structure, consisting of three pressurized tubes on which a textile is stretched, theinteriorofthestructurethusformedbeingdepressed.Figure12showstheroofofthePlacedesFestivals,madeofaircushions.One of the most emblematic pavilions was the Fuji pavilion, consisting of 16 tubes of 4mdiameterinflated,withalengthof78m.
Enthusiasm for these innovative structureswas important in the sixties, andmanybooksandpublicationsmentiontheminthefieldofarchitectureandinthe fieldofdimensioning.Amongtheseworks,mentioncanbemadeinparticularofthebookofThomasHerzog,whichincludesboth aspects. During the sixties and seventies, numerous and different pneumatic structureswerebuilt,exploitingtheverylargenumberofpossiblepotentialforms,dependingonwhetherthe internal pressure is greater or smaller than the atmospheric pressure, orwhether or nottherearesupportpoints,or linearsupportsoftenmadeofcables. Inhisbook,ThomasHerzogproposes a classification of the different possible forms. Here we just present the maindistinctionsthathemade,soastobringoutthehugevarietiesofpotentialarchitecturalforms.Adistinctionisdonebetweenlowpressuresystems(from10to100mmofwatercolumn),andsystemswithhighpressure(2000to70000mmofwatercolumn).Themaindifference isthathigh-pressuresystemsarestructuralparts.Lowpressuresystems:For low pressure structures, support point and linear support (oftenmade of cables) can beused,whichmainlyallowsreducing theradii in thecurvatureswhichhasagreat influenceonthey-tensionsinthefabrics.
Thetwofollowingtablepresentthevarietyofformsforlowandhighpressureforlow-pressuresystems.Low-pressuresystemscanbemono-membraneordoublemembranesstructures.Notethat even if the great majority of pneumatic structures are with positive pressure, negativepressureoffer alsovery interesting forms.Herzogmentioned that for thesenegativepressurestructures,thedisadvantagesarethesnowandwaterpocketsandtheinstabilityofformduetoaerodynamic loadings, but that “in combination with positive pressure systems and highpressuretubularstructures,itcanbeverysuitableforsomepurposes”.Table:variablesformsforpneumaticstructuresforlowpressuresystem(reproductionoftablep33)
Influenceoftheradiusofcurvature:Thefigureillustratesthebasicprinciplesofmono-membranesandtheinfluenceofthepressureandtheradiusbecausethetensioninthefabricisproportionaltothepressureandtheradiusofcurvature.Tobuilda10-mbubblemono-membraneinflatedstructure,andcovera20mlength,thetensionTisobtainedwithT=pR/2,wherepisthepressureandRtheradius.Coveringadouble length by doubling the radius leads to doubling the tensions in the fabric. If it isnecessary to reduce the height because of the aerodynamics loadings on the structure forexamplewithonlyabubble(caseC),theradiusincreasesalso(multipliedwith2,5here).Finally,supportscanbeusedtoassemble10mradiuscontiguousformstoeachother.Inthelastcase(caseD),thetensioninthefabricsandtheheightofthestructurearethesamethanforcaseA,andthecoveredsurfaceismuchhigher.
Highpressuresystems:
High-pressure pneumatic membrane structures consist mainly of tube-like elements. Thepressureinsidethestructureincreasesitsstiffnessandallowsthestructureresistingtoexternalloadings.lnordertodistinguishbetweenhighpressuresystemsthefollowingfeaturesshouldbetakenintoaccount:
2.4. LargeAirsupportedroofs:Pneumatictextilescoverturehavebeenusedforroofingtocoverlargestructuresmainlyduringthe70sandthe80s,inspiredbytheUSpavilionatOsakaexposure.Therewereseveraldecadesof“classical”construction.HereoneortwoemblematiclargeairsupportedroofsinEuropeTheproblemoftheMinessotaMetrodome:Designing such structures imposes to the designer to clearly identified the scenarios that canlead to a failure or a collapse. Even if the potentially failure causes have been identified, badconjunction of events can also lead to disaster. In pneumatic architecture, one of the mostemblematic failure is theoneof theMetrodomeMinessota(Fig.9).Thisstructurewasmadeoftwo membranes, air being continuously inflated between two layers of fabric to ensure itsbearingcapacities. InDecember2010, theweightofamassiveaccumulationof snowdue toavery severe stormovercame the loading capacity of themembrane,whichwas finally torn inseverallocationsandcollapsed.Thewindhadabiginfluencealso,notonamechanicallypointofview,butbecauseworkerswhoserolewastopartiallyremovethesnowwhereunabletoaccesstotheroofofthedome.Thiswasreinforcedbytheactthattheothersmeasuresthathadbeenthought to counteract the effect of the snowwere inadequate, like significantly increasing thetemperaturewithin the stadium. This collapse shows that particular scenarios can occur andthat the consequences can be important (economic consequences, because of repairs andtransferssportingeventsinotherstages).Anotherconsequenceisthatitcangeneratedistrustinthiskindofstructure.
During the lastdecades,someroofsweredismantled,someof themreplacedwithsteelstrussand fabric roof. This was the case for example of theBC Place,Vancouver,BritishColumbia,Canada,whichwasformerlythelargestair-supportedstadiumintheworld.Theroofwas changed to a retractable roof in 2011, theDakotaDome,Vermillion, SouthDakota,UnitedStates,forwhichtheair-supportedroofwasreplacedbyasteelframedomedroofin200,ortheYuengling Center,Tampa, Florida, United States, where the air-supported Teflon/Fiberglassroofwasreplacedwithasteelframe-supportedroofin2012.But some notable air-supported domes are always in operation: (source Wikipedia), Bennett Indoor Athletic Complex, Toms River, New Jersey, United States, Dalplex (athletics complex), Halifax, Nova Scotia, Canada, Greater Binghamton Sports Complex, Binghamton, New York, United States, Harry Jerome Sports Center, Burnaby, British Columbia, Canada, Krenzler Field, Cleveland State University, Cleveland, Ohio, United States, Tokyo Dome, Tokyo, Japan
Inflatablestructuresthereforehadaprolificdevelopmentalperiodinthe1960sand1970s,forboth lowpressureandhigh-pressurestructures.Thiscrazewas thenconsiderablyreduced, inparticularbecauseoftheenergycrisesduringtheeighties.In recent years, there has been a return of these structures, both formono-membranes (air-halls), for air-inflated structures (cf the Ontario celebration Pavillon zone, or the deployablehangarthatprotectstheplaneSolarImpulsaroundtheworld),butalsobecauseoftheimportantdevelopments of the inflatable cushions, the appearance of the tensairity to confer inflatablebeamsveryimportantrigidity,andarenewintheexploitationoftheinfinitepossibleformsofpneumaticsinartandarchitecture.
Here:Wikipedia: [1] In the 1980s, a number of inflatable cushion systems were documented.[2] [3] [4] [5] [6] Before 2000, most inflatable air cushions used a single check valve as described in US patent 5445274. However if one part of the cushion was punctured then this packaging would completely deflate. In 2002, several types of continuously independent one way air valve films were introduced, such as US patent 6913803, "One-way valve for inflatable package" by 3M. These patents incorporated a one way air valve film, which can be produced continuously and independently. If one air tube is punctured, the other air tubes will still remain inflated.
Pictures : Grenn House for the botanic, Allianz Arena (to be finished)
4.2. Tensairity:inflatedreinforcedbeams
In2000,Dr.MauroPedretti,aSwisscivilengineer,hadtheideatoreinforceinflatedbeamswithcablesandstrutsinordertoimprovetheloadbearingcapacityofthesystem.Anewlight-weightstructuralconceptwasborn,whichwaslaternamedTensairity,anacronymfortension,airandintegrity. The company Airlight Ltd was set up in Biasca, Switzerland by Mauro Pedretti tocommercializethenewstructure.In2001MauroPedrettienteredacollaborationwiththeSwisscompany prospective concepts AG, which was famous for their work with inflatables, inparticularfortheir inflatablemannedairplaneStingray.Dr.RolfLuchsinger joinedprospectiveconcepts inthebeginningof2002totakeovertheR&DofTensairity,whileAirlightstartedtofocus their efforts on applications of Tensairity. A demonstrator car bridgewas built in 2002whichwasthefirstpublicpresentationoftheTensairitytechnologyonJune26thataneventofprospective concepts. In the coming years, the technology was continuously improved andAirlightwasabletorealizeanumberofTensairitystructures.TheroofoftheparkinggarageinMontreuxin2004alreadyshowedthefullpotentialoftheTensairitytechnology.Askiersbridgein France 2005proofed the load bearing capacity of Tensairity and iswith its 52m span thelargestTensairitystructuresofar.
In 2006, the R&D activities of prospective concepts were transferred to the newly foundedCenter for Synergetic Structures, a public private partnership between the Swiss FederalResearch Institute Empa and prospective concepts. Headed by Rolf Luchsinger, the CenterscrutinizedthestructuralbehaviourofTensairityinthecomingyears.Dedicatedtestrigswerebuilt, detailed FEM models developed and material properties measured in order to fullyunderstand, optimize and furtherdevelop the system.Thiswork led to a numberof scientificpapers which attracted the interest from researchers all over the world. Roberto Maffei andPaolo Beccarelli, both PhD students at TU Milano, started to devote their research to fabricstructures and Tensairity around 2010. The fruitful collaboration between these researchersandtheCenterforSynergeticStructureseventually ledtotherealisationofthefirstTensairitypaddockstogetherwithCarloDusinafrom3Btendein2014.OnDecember22th,2014,RobertoMaffei,RolfLuchsinger,PaoloBeccarelli,CarloDusinaandFrancoBrescianifoundedTensairitySolutionssrl.
Theinflatablestructuresalsostrongly inspireartistsandbuilders,usingtheir imaginationandthespecificpropertiesoftheinflatableintermsofparticularforms,tocreateveryspecialeffects,as theLeviathanexhibitedamongothers in theGrandPalaisofParis in2011,where thepureform and geometry strongly contrasts with the metal structures of the early 20th century.Invitedtoproduceahugework,AnishKapoorproducedaformandacolorspecificallyadaptedto the immensity and the Art Nouveau style of the Nave. The artist played on the dualities:animate/inanimate,open/closed,interior/exterior,full/empty,light/dimness,painting/sculpture.
Inthesameway,innovativeformsappearinthebuildings,withastrongvisualimpact,suchastheteahouse,whichisaairmastress(lowpositivepressurewithpointsupports),ortheThirstpavilionof the “WaterandSustainableDevelopment "that tookplace inSaragossaduring thesummerof2008.
6. Studiesandresearch
TheresearchworkofFreiOttowasapioneer,particularlyinthefieldofformresearch,andwaspublished in1962.The first InternationalSymposiumonPneumaticStructureswasorganizedon 11 and 12 May 1967 in Stuttgart by the IASS and hosted by Frei Otto (ref Stuttgartconference). This symposium was dedicated to the key points of the design of membranestructures, and brought together emblematic actors of this new technology in full evolution:WalterBird,VictorLundy,etc…Afterafirstpointconcerningthegeneraldevelopmentandthearchitecturalaspectsofpneumaticstructures,differentachievementswerepresented,followedbyanalysesofmembranestructures,non-linearmembranecomputationandnumericalanalysis.
Figure21:theLeviathanintheGrandPalais,Paris
Figure22:InsidetheLeviathan
Figure24:theteaHouse Figure23:theThirstPavillon
Partoftheconferencewasalsodevotedtostructuraltesting(windtunnel)andmaterialstesting.Inaddition,thisconferencewasafirstopportunitytoestablishthevocabularyofthisnewandinnovative technology: air supported, air-inflated, etc. Following this first event dedicated topneumatic structures, other symposiumor colloquiumwere organised, allowing to follow theprogress in the different topics: architecture, form-finding, design and various calculationmethods, external loading determination, material modelling, patterning, manufacturing,maintenanceandsafety.1972:Int.SymposiumonPneumaticStructures,IASS,Delft,1972.1977:SymposiumInternationalsurlesStructuresGonflables-ClBVenice,June19771980: Symposium on Air-supported structures: the state of the art, organized by par TheInstitutionofStructuralEngineers,London...Internationalconferenceontextilecompositesandinflatablestructures(1to9th)…Tensinetsymposiums:Istambul,NewcastleMilanAdvances in all areas related tohavealsobeen the subject ofnumerouspublications inmanyrenownedjournals,likethin-walledstructures,structuralengineering,J.WindEngandIndustrial...Aerodynamicsciteotherjournals?ResearchinEurope:AtNantesUniversity(inflatablebeams:static,dynamics,buckling,fluid structure interaction, reliablity), At Munich University (former project KUBletzinger),and?...references:tobeaddedhereorattheendoftheguide
