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CSE Research Bulletin

ISSN 0219-0370 January 2001 NO. 14

Research Collaboration with Industry

The School has long recognised the need for and value of conducting collaborative research and development with industry. Over the years, close links have been forged with the local public and private sectors as a necessary strategy for nurturing professional and research manpower relevant to industry's needs, while at the same time advancing the School's academic and research interests. This is in line with NTU's aspiration to become a university of industry. On a formal level, several Research Centres of excellence have been established within the School in partnership with local public sector organisations. Numerous Memoranda of Understanding (MOUs) have also been signed for joint research studies in the various disciplines of civil engineering. In this article, we highlight some of the School's collaborative research activities with local industry partners.

The Geotechnicial Research Centre (GRC) was established jointly with the PWD Corporation (Formerly the Public Works Department) to promote sound geotechnical practice through research and development. The Centre has since launched many research and development projects with government organisations, statutory boards and industry. One example is the GRC‘s on-going collaboration with SPECS Consultants Pte Ltd in the area of land reclamation. The Centre offers an MSc programme in GeotechnicalEngineering. It also organises seminars, workshops, conferences and short courses to provide continuing education and training, and to facilitate technology transfer to local professionals. Technical services provided to the public and private sectors include planning, design and construction of geotechnical works; specialised laboratory and field-testing; and dissemination of information on current research and development in geotechnical engineering.

The Centre for Advanced Construction Studies (CACS) was the fist research centre established within the School in partnership with the Building and Construction Authority (BCA) (formerly the Construction and Industry Development Board, CIDB). The Centre's main aim is to broaden the knowledge, skills and technological expertise of local professionals in construction technology and management. High-level professional training is provided through a Master of Science degree course (MSc) in International Construction Management, and a Postgraduate Diploma Course in Construction Management. The courses are conducted jointly with the BCA and the Institution of Engineers, Singapore. Technology transfer to industry is implemented through workshops, seminars, conferences and international exchange programmes. The BCA provides useful feedback from local industry and helps the Centre establish effective links with international organisations. The Centre has recently conducted a joint research study with the Ministry of Manpower (MOM) on

The Protective Technology Research Centre (PTRC) was set up jointly with the Ministry of Defence (MINDEF) to spearhead research and development in advanced protective technology, as well as to provide professional education and technology transfer. The Centre has signed MOUs with the National Centre for Research on Earthquake Engineering (NCREE) to support an experimental research programme on reinforced concrete beam-column joints, and with the College of Engineering at Pennsylvania State University in the USA to

file:///D|/CEE_old/RESEARCH/Bulletin/2000_2001/HTM/INDEX.HTM (1 of 5)9/27/2003 10:52:17 AM

http://www.ntu.edu.sg/grc/enter.htm


http://www.pwdcorp.com.sg/

http://www.ntu.edu.sg/cacs/

http://www.bca.gov.sg/

http://www.ies.org.sg/

http://www.mom.gov.sg/


http://www.ntu.edu.sg/ptrc/


http://www.mindef.gov.sg/



equitable allocation of manpower in the construction industry, and with the Land Transport Authority (LTA) on quantity surveying and cost control, with a focus on the labour constants of civil engineering trades. The Centre is also collaborating with the BCA to study the experiences of countries like Sweden, Holland and Finland in developing measures that could help nurture promising Singaporean contractors to become world-class players.

conduct short courses on Protective Structures.

The Environmental Engineering Research Centre (EERC) was set up in partnership with the Ministry of the Environment (ENV). The EERC serves as a focal point for synergistic R&D collaborations with leading government agencies, industry partners and educational and research institutions both locally and around the world. Key areas of research include membrane technology, environmental biotechnology, environmental remediation, environmental hydraulics, environmental management, and waste recycling and reuse. The EERC currently manages about 36 projects with an estimated total budget of $7.6 million. It has active collaborations with major local environmental organisations including the ENV and the Public Utilities Board. The EERC’s overseas collaborators include the University of Cambridge, Imperial College, Stanford University, the University of New South Wales, National Taiwan University, Kyoto University and Korea Advanced Institute of Science and Technology.

The Centre for Transportation Studies (CTS) was set up with the mission to serve Singapore and the Asia-Pacific region. The CTS conducts research on issues related to air, land and sea transportation relevant to Singapore and the region. Many of the projects are jointly conducted with partners from industry, which include the Civil Aviation Authority of Singapore (CAAS), Jurong Town Corporation (JTC), the Land Transport Authority (LTA), the Maritime and Port Authority (MPA), NatSteel Ltd, SMRT Ltd, and the Traffic Police Department. The main areas of research include transport planning and modelling, traffic management and road safety, intelligent transportation systems, as well as pavement materials and technology. Recently, the Centre completed several contract research studies for the LTA including traffic signal operation in conjunction with the green signal countdown device, a perception survey on the revised left-turn-on-red signage, a perception survey on speed limits and speeding and a review of guidelines/practices for variable signs for use in Singapore. The Centre has also started on a study for VICOM and the Traffic Police involving the analysis of historical data to identify trends and causes of road accidents.

the formation of sandbars at drainage outlets; the impact of rainwater from buildings without roof gutters; the management of quantity and quality of storm runoff using infiltration pits and the utilisation of marine clay as innovative building and construction materials.

Over the years, the School has also co-operated with Jurong Town Corporation (JTC), the Marine and Port Authority (MPA), the Housing and Development Board (HDB), and the Public Works Department (PWD), on a range of research projects. Joint studies with the JTC include one on the characterisation of soils in reclamation works, and another on sand accretion in


http://www.lta.gov.sg/index.htm

http://www.ntu.edu.sg/centr/wwweerc/eerc.htm


http://www.env.gov.sg/


http://www.ntu.edu.sg/home/cshlam/cts/centre.html

http://www.caas.gov.sg/

http://www.jtc.gov.sg/



http://www.mpa.gov.sg/





http://www.hdb.gov.sg/




Joint study with ENV on sandbar formation at Opera Estate outlet drain

The University signed a Memorandum of Understanding (MOU) with the Ministry of the Environment (ENV) in 1991 for the purpose of establishing closer co-operation in applied research and development in the areas of environmental management, infrastructure, and waste treatment and reuse. In 1999, an expanded MOU was signed between the two institutions to enhance research collaboration and to provide a framework for NTU and ENV to jointly develop training courses in environmental management. Some of the recent projects initiated under the MOU include : studies on

Singapore waters. The latter involves an extensive review of field data, numerical and physical modelling, as well as small-scale field experiments, to locate regions where sediment accretion is likely to occur. The collaborative studies with the MPA include a project on Coastal Zone Resources Mapping using GIS, which is funded by Phase II of the Australian-Asean Environmental Cooperation Program. The study aims to set up a framework and data structure to map maritime resources, manage the use of sea space and investigate other related issues using the Geographic Information System (GIS). One test case relates to the use of GIS to combat oil spill. The School has collaborated with the HDB on a study of the behaviour of reinforced concrete columns confined by welded-wire fabric. A feasibility study on the potential of constructing tunnels, caverns and underground spaces in Bukit Timah granite for various uses was carried out jointly with the PWD. Among the local private sector organisations which the School has collaborated with are Spandeck Engineering (S) Pte Ltd, to improve the use of hollow core concrete slabs in the construction industry, L & M Pre-stressing Pte Ltd on the development of building repair technology, McDermott South East Asia Pte Ltd on tubular joints of offshore structures, and Shimizu Corporation on the performance of large caissons for the Republic Plaza.

Besides research and development linkages with local industry, the School also takes a pro-active approach in pursuing research collaborations with overseas research and academic institutions. Such research collaborations help to optimise the utilisation of available manpower and physical resources, and at the same time allow staff members to keep abreast of the latest developments and trends in leading overseas institutions. Research collaborations with overseas academic and research institutions will be highlighted in a later issue.




Clean Water Forum

A Clean Water Forum was jointly organised by Nanyang Technological University, Stanford University, the Public Utilities Board and the Ministry of the Environment on 28 June 2000. The Forum provided a platform for top public sector leaders, senior industry executives and scientists to hold discussions on Singapore’s water issues. Mr Lim Swee Say, Minister of State for Trade and Industry was the Guest of Honour. During the Forum, five Stanford University professors shared their insights from a quarter of a century of clean water research at Stanford University. The Stanford team was led by Professor James Leckie, the Director of the Environmental Engineering and Science (EES) Programme at Stanford University. EES has been ranked the top environmental engineering programme in the United States for many years. In his opening address, Mr Lim highlighted the need to adopt an innovation-driven mindset in the quest for creative solutions to meet the growing demand for clean water in Singapore. By teaming up with research institutions both locally and abroad, it is hoped that

Mr Lim Swee Say, Minister of State for Trade and Industry, delivering the opening address at the Clean Water Forum

the PUB and ENV will be in a better position to stay abreast of cutting-edge water technology. This will help ensure that Singapore continues to have a safe and reliable water supply.

Chief Defence Scientist Commissions Large Diameter Split Hopkinson Pressure Bar Facility at the Protective Technology Research Centre (PTRC)The Chief Defence Scientist (CDS), Prof. Lui Pao Chuen, and a number of senior Defence Science and Technology Agency (DSTA) officials visited the Protective Technology Research Centre (PTRC) in the School of Civil and Structural Engineering (CSE) and attended a briefing on PTRC’s research activities. The CDS and DSTA officials were also briefed on the capability of the 75 mm diameter split Hopkinson pressure bar facility which was set up as part of a collaborative project funded by the DSTA to investigate the dynamic response of brittle engineering materials at high strain rate. High strain rate occurs when natural or man-made engineering materials are subjected to short duration impact, shock or air-blast loading.

Prof. Lui officially commissioned the equipment by releasing pressurised gas, which propelled a specially designed linearly-shaped impactor to the incident bar. This action sets up a series of shock waves that are transmitted to a specimen. The loading waveform resulting from the impact shows a significant delay of the rise-time and, in turn,

Following the commissioning of the split Hopkinson pressure bar, a separate visit to the Centre was made by senior officials led by Rear-Admiral Richard Lim (Deputy Secretary – Technology, MINDEF) and Brigadier-General Sin Boon Wah (Deputy Chief Executive Officer – Strategic Development, DSTA). The group, comprising officials from the Defence Technology and Resource Office, DSTA and Defence Medical Research Institute, was updated on current developments and on future research work within PTRC. Future work by the Centre on defence medical research related to ballistics effects on the human body was discussed.


http://www.pub.gov.sg/



enables uniform stress to develop on a large diameter Bukit Timah granite specimen. Measured incident and reflected strain history was analysed to obtain the dynamic characteristics of the specimen. Results of the constant strain rate history occurring over the short duration provides evidence of test accuracy and confirms the testing methodology on large diameter brittle engineering materials.

Prof. Lui (second from right) being briefed on the capability of the large diameter split Hopkinson pressure bar

RADM Richard Lim (second from left) being briefed on the mechanics of wave propagation and data acquisition by the Project Principal Investigator

Please read the DISCLAIMER before you begin exploring the CSE Research Bulletin.

Copyright 2001 School of Civil & Structural Engineering, NTU. All rights reserved.


CSE Research Bulletin No. 14. January 2001: In Focus

ISSN 0219-0370 January 2001 NO. 14

Research Collaboration with Industry

The School has long recognised the need for and value of conducting collaborative research and development with industry. Over the years, close links have been forged with the local public and private sectors as a necessary strategy for nurturing professional and research manpower relevant to industry's needs, while at the same time advancing the School's academic and research interests. This is in line with NTU's aspiration to become a university of industry. On a formal level, several Research Centres of excellence have been established within the School in partnership with local public sector organisations. Numerous Memoranda of Understanding (MOUs) have also been signed for joint research studies in the various disciplines of civil engineering. In this article, we highlight some of the School's collaborative research activities with local industry partners.

The Geotechnicial Research Centre (GRC) was established jointly with the PWD Corporation (Formerly the Public Works Department) to promote sound geotechnical practice through research and development. The Centre has since launched many research and development projects with government organisations, statutory boards and industry. One example is the GRC‘s on-going collaboration with SPECS Consultants Pte Ltd in the area of land reclamation. The Centre offers an MSc programme in GeotechnicalEngineering. It also organises seminars, workshops, conferences and short courses to provide continuing education and training, and to facilitate technology transfer to local professionals. Technical services provided to the public and private sectors include planning, design and construction of geotechnical works; specialised laboratory and field-testing; and dissemination of information on current research and development in geotechnical engineering.

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The Centre for Advanced Construction Studies (CACS) was the fist research centre established within the School in partnership with the Building and Construction Authority (BCA) (formerly the Construction and Industry Development Board, CIDB). The Centre's main aim is to broaden the knowledge, skills and technological expertise of local professionals in construction technology and management. High-level professional training is provided through a Master of Science degree course (MSc) in International Construction Management, and a Postgraduate Diploma Course in Construction Management. The courses are conducted jointly with the BCA and the Institution of Engineers, Singapore. Technology transfer to industry is implemented through workshops, seminars, conferences and international exchange programmes. The BCA provides useful feedback from local industry and helps the Centre establish effective links with international organisations. The Centre has recently conducted a joint research study with the Ministry of Manpower (MOM) on equitable allocation of manpower in the construction industry, and with the Land Transport Authority (LTA) on quantity surveying and cost control, with a focus on the labour constants of civil engineering trades. The Centre is also collaborating with the BCA to study the experiences of countries like Sweden, Holland and Finland in developing measures that could help nurture promising Singaporean contractors to become world-class players.

The Protective Technology Research Centre (PTRC) was set up jointly with the Ministry of Defence (MINDEF) to spearhead research and development in advanced protective technology, as well as to provide professional education and technology transfer. The Centre has signed MOUs with the National Centre for Research on Earthquake Engineering (NCREE) to support an experimental research programme on reinforced concrete beam-column joints, and with the College of Engineering at Pennsylvania State University in the USA to conduct short courses on Protective Structures.

The Environmental Engineering Research Centre (EERC) was set up in partnership with the Ministry of the Environment (ENV). The EERC serves as a focal point for synergistic R&D collaborations with leading government agencies, industry partners and educational and research institutions both locally and around the world. Key areas of research include membrane technology, environmental biotechnology, environmental remediation, environmental hydraulics, environmental management, and waste recycling and reuse. The EERC currently manages about 36 projects with an estimated total budget of $7.6 million. It has active collaborations with major local environmental organisations including the ENV and the Public Utilities Board. The EERC’s overseas collaborators include the University of Cambridge, Imperial College,



http://www.bca.gov.sg/

http://www.ies.org.sg/













Stanford University, the University of New South Wales, National Taiwan University, Kyoto University and Korea Advanced Institute of Science and Technology.

The Centre for Transportation Studies (CTS) was set up with the mission to serve Singapore and the Asia-Pacific region. The CTS conducts research on issues related to air, land and sea transportation relevant to Singapore and the region. Many of the projects are jointly conducted with partners from industry, which include the Civil Aviation Authority of Singapore (CAAS), Jurong Town Corporation (JTC), the Land Transport Authority (LTA), the Maritime and Port Authority (MPA), NatSteel Ltd, SMRT Ltd, and the Traffic Police Department. The main areas of research include transport planning and modelling, traffic management and road safety, intelligent transportation systems, as well as pavement materials and technology. Recently, the Centre completed several contract research studies for the LTA including traffic signal operation in conjunction with the green signal countdown device, a perception survey on the revised left-turn-on-red signage, a perception survey on speed limits and speeding and a review of guidelines/practices for variable signs for use in Singapore. The Centre has also started on a study for VICOM and the Traffic Police involving the analysis of historical data to identify trends and causes of road accidents.

Joint study with ENV on sandbar formation at Opera Estate outlet drain

the formation of sandbars at drainage outlets; the impact of rainwater from buildings without roof gutters; the management of quantity and quality of storm runoff using infiltration pits and the utilisation of marine clay as innovative building and construction materials.

Over the years, the School has also co-operated with Jurong Town Corporation (JTC), the Marine and Port Authority (MPA), the Housing and Development Board (HDB), and the Public Works Department (PWD), on a range of research projects. Joint studies with the JTC include one on the characterisation of soils in reclamation works, and another on sand accretion in Singapore waters. The latter involves an extensive review of field data, numerical and physical modelling, as well as small-scale field experiments, to locate regions where sediment accretion is likely to occur. The collaborative studies with the MPA include a project on Coastal Zone Resources Mapping using GIS, which is funded by Phase II of the Australian-Asean Environmental Cooperation Program. The study aims to set up a framework and data structure to map maritime resources, manage the use of sea space and investigate other related issues using the Geographic Information



http://www.caas.gov.sg/













The University signed a Memorandum of Understanding (MOU) with the Ministry of the Environment (ENV) in 1991 for the purpose of establishing closer co-operation in applied research and development in the areas of environmental management, infrastructure, and waste treatment and reuse. In 1999, an expanded MOU was signed between the two institutions to enhance research collaboration and to provide a framework for NTU and ENV to jointly develop training courses in environmental management. Some of the recent projects initiated under the MOU include : studies on

System (GIS). One test case relates to the use of GIS to combat oil spill. The School has collaborated with the HDB on a study of the behaviour of reinforced concrete columns confined by welded-wire fabric. A feasibility study on the potential of constructing tunnels, caverns and underground spaces in Bukit Timah granite for various uses was carried out jointly with the PWD. Among the local private sector organisations which the School has collaborated with are Spandeck Engineering (S) Pte Ltd, to improve the use of hollow core concrete slabs in the construction industry, L & M Pre-stressing Pte Ltd on the development of building repair technology, McDermott South East Asia Pte Ltd on tubular joints of offshore structures, and Shimizu Corporation on the performance of large caissons for the Republic Plaza.

Besides research and development linkages with local industry, the School also takes a pro-active approach in pursuing research collaborations with overseas research and academic institutions. Such research collaborations help to optimise the utilisation of available manpower and physical resources, and at the same time allow staff members to keep abreast of the latest developments and trends in leading overseas institutions. Research collaborations with overseas academic and research institutions will be highlighted in a later issue.




Clean Water Forum

A Clean Water Forum was jointly organised by Nanyang Technological University, Stanford University, the Public Utilities Board and the Ministry of the Environment on 28 June 2000. The Forum provided a platform for top public sector leaders, senior industry executives and scientists to hold discussions on Singapore’s water issues. Mr Lim Swee Say, Minister of State for Trade and Industry was the Guest of Honour. During the Forum, five Stanford University professors shared their insights from a quarter of a century of clean water research at Stanford University. The Stanford team was led by Professor James Leckie, the Director of the Environmental Engineering and Science (EES) Programme at Stanford University. EES has been ranked the top environmental engineering programme in the United States for many years. In his opening address, Mr Lim highlighted the need to adopt an innovation-driven mindset in the quest for creative solutions to meet the growing demand for clean water in Singapore. By teaming up with research institutions both locally and abroad, it is hoped that

Mr Lim Swee Say, Minister of State for Trade and Industry, delivering the opening address at the Clean Water Forum

the PUB and ENV will be in a better position to stay abreast of cutting-edge water technology. This will help ensure that Singapore continues to have a safe and reliable water supply.

Chief Defence Scientist Commissions Large Diameter Split Hopkinson Pressure Bar Facility at the Protective Technology Research Centre (PTRC)The Chief Defence Scientist (CDS), Prof. Lui Pao Chuen, and a number of senior Defence Science and Technology Agency (DSTA) officials visited the Protective Technology Research Centre (PTRC) in the School of Civil and Structural Engineering (CSE) and attended a briefing on PTRC’s research activities. The CDS and DSTA officials were also briefed on the capability of the 75 mm diameter split Hopkinson pressure bar facility which was set up as part of a collaborative project funded by the DSTA to investigate the dynamic response of brittle engineering materials at high strain rate. High strain rate occurs when natural or man-made engineering materials are subjected to short duration impact, shock or air-

Following the commissioning of the split Hopkinson pressure bar, a separate visit to the Centre was made by senior officials led by Rear-Admiral Richard Lim (Deputy Secretary – Technology, MINDEF) and Brigadier-General Sin Boon Wah (Deputy Chief Executive Officer – Strategic Development, DSTA). The group, comprising officials from the Defence Technology and Resource Office, DSTA and Defence Medical Research Institute, was updated on current developments and on future research work within PTRC. Future work by the Centre on defence medical research related to ballistics effects on the human body was discussed.


http://www.pub.gov.sg/



blast loading.

Prof. Lui officially commissioned the equipment by releasing pressurised gas, which propelled a specially designed linearly-shaped impactor to the incident bar. This action sets up a series of shock waves that are transmitted to a specimen. The loading waveform resulting from the impact shows a significant delay of the rise-time and, in turn, enables uniform stress to develop on a large diameter Bukit Timah granite specimen. Measured incident and reflected strain history was analysed to obtain the dynamic characteristics of the specimen. Results of the constant strain rate history occurring over the short duration provides evidence of test accuracy and confirms the testing methodology on large diameter brittle engineering materials.

Prof. Lui (second from right) being briefed on the capability of the large diameter split Hopkinson pressure bar

RADM Richard Lim (second from left) being briefed on the mechanics of wave propagation and data acquisition by the Project Principal Investigator

Please read the DISCLAIMER before you begin exploring the CSE Research Bulletin.

Copyright 2001 School of Civil & Structural Engineering, NTU. All rights reserved.


CSE Research Bulletin No. 14. January 2001: Research Projects

ISSN 0219-0370 January 2001 NO. 14

GPS Reference Station Network for Instant Accurate Tracking

The School is collaborating with the University of New South Wales, Australia and the Survey Department of Singapore to develop a multi-base Global Positioning System (GPS) in Singapore to prototype real-time high precision solutions. Such high precision positioning techniques are the result of progressive R&D innovations. The advantages of the multi-base station approach include : overcoming the short baseline constraint for present off-the-shelf commercial RTK (real time kinematic) systems; improving the speed for ambiguity resolution (AR) thus allowing instantaneous on the fly AR; providing real-time differential correction access to multiple users concurrently; and improving the relative accuracy using either dual-frequency or single frequency GPS rover receivers. This joint project is expected to change the way measurements are made in engineering work and large-scale land surveys in Singapore. The principal investigator is A/P Goh Pong Chai ([email protected]).

Components of Singapore GPS Reference

Station Network

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mailto: [email protected]


Variable Message Signs (VMS)

The Centre for Transportation Studies conducted a study for the Land Transport Authority (LTA) to assess the current road signs used in the Expressway Monitoring & Advisory system (EMAS). The size, background colours and other features of these signs were analysed according to factors such as conspicuity, readability and comprehensibility. The current specifications were compared with standards and practices adopted in Europe, the USA and Australia. The locations of the travel time signs near entries to expressways were also analysed, making use of the fundamental parameters of driver perception and reaction to sign information. Project investigators : James Luk ([email protected]), Michael Lam and Henry Fan

Joint study with LTA: An expressway VMS can also display travel time information

Biotechnological Application on Wastewater Treatment

The project looks into various anaerobic processes such as upflow anaerobic sludge blanket (UASB) reactors, biofilters and hybrid reactors in treating high strength wastewater. Specific attention has been focused on the granulation of biomass in UASB, the development of trapped suspended biomass in biofilters, and a hybrid process for wastewater containing high levels of recalcitrant substances. Investigators : Prof Tay Joo Hwa & Ast/P Show Kuan Yeow ([email protected])

Bio-Reactors Set-up





Conversion of Sludge Generated during Rainwater Treatment into Useful Products for the Construction Industry

This project examines the feasibility of reusing sludge generated from rain water treatment and ship blasting wastewater treatment in a shipyard as commercial products. A substantial amount of sludge is being generated and the disposal problem can be alleviated if the sludge can be converted into useful resources. This project studies the feasibility of converting the sludge into construction materials such as lightweight aggregates, bricks, pavement blocks, and other materials. Investigator : Prof Tay Joo Hwa & Ast/P Show Kuan Yeow ([email protected])

Sintered High Strength Aggregates from Sludge

Other recently approved research projects are summarised below. You are welcome to email the investigators concerned for more information on their projects. PROJECT TITLES PRINCIPAL INVESTIGATORCapillary Barrier for Slope Stabilisation (Collaboration with University of Saskatchewan, Canada and University of Durham, UK)

A/P H Rahardjo ([email protected]) A/P Leong EC Prof DG Fredlund (Univ of Sask.) Prof GW Wilson (Univ of Sask.) Dr DG Toll (Univ of Durham)

Dynamic Buckling Analysis of Structures Subjected to Vertical Ground Excitations

A/P Hao Hong ([email protected]) Prof Cheong HK

Size Effect on Shear Strength of Concrete (Collaboration with National Technical University of Athens and Imperial College, UK)

A/P Tan KH ([email protected]) Prof Cheong HK Prof Michael D Kotsovos (Nat. Tech. Univ. of Athens) Prof Milija N Pavlovic (Imperial College)

Experimental Investigation of Thin-Walled Structural Steel Connections (Inter-School Project)

Ast/P Ben Young ([email protected]) A/P Chou Siaw Meng (School of MPE)

Dynamic Structural Response Monitoring of Tall Buildings using GPS (Inter-School Project)

A/P JMW Brownjohn ([email protected]) A/P Law Choi Look (School of EEE) A/P Tor YK

Design of Reinforced Concrete Shear Wall with Opening-Strut-and-Tie Approach

Ast/P Li Bing ([email protected]) A/P Tan Kang Hai










The Behaviour of Joints in Tunnel Linings Ast/P NF MacAlevey ([email protected]) Ast/P AM Hefny A/P Lok Tat Seng



CSE Research Bulletin No. 13. January 2000: Research Activities

ISSN 0219-0370 January 2001 NO. 14

Inside this issue, there are thirty-four technical articles highlighting the School’s research activities in the areas of Construction, Environment, Geotechnics, Structures, Surveying, Transportation and Water. You are welcome to email the respective authors to find out more about their work.

All the research articles are available in the form of PDF (portable document file) format. If you do not

have PDF, please click to download and install the Acrobat Reader for Windows 95, Windows 3.1, Window-NT, DOS, Macintosh, OS2, LINUX, etc. To view and print the articles, run Acrobat Reader and click the links below. Construction

● Seismic Behaviour of Connection between Precast Concrete Beams

● Seismic Performances of Reinforced Concrete Frames Under Low Intensity Earthquake Effect

● Seismic Resistance of Reinforced Concrete Beam-Column Joints with Non-ductile Details

● Strengthening of One-way Slabs Using Carbon Fibre Plates : The Effect of Preload

● Behaviour of Mortar under Tri-axial Stress● Testing of Concrete under High

Temperature

Environment

● Waste Human Hair as a Renewable Sorbent for Oil-spill Cleanup

● Microbiological Investigations of Aerobic Granules for Enhanced Biological Wastewater Treatment

● Converting Industrial Sludge-Marine Clay Mixes into Aggregates for Concrete

● Oxidative Bacterial Destruction using MPCO prior to RO Desalination

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http://www.adobe.com/prodindex/acrobat/readstep.html


Geotechnics

● Analysis of Laterally Loaded Pile using Constrained Optimization

● Rainfall-Induced Slope Failures: Mechanism and Assessment

● Undrained Cavity Expansion in Modified Cam Clay

● Application of Cavity Expansion Theory to the Interpretation of Piezocone Test in Clay

● A Variational Solution for Laterally Loaded Single Piles

Surveying

● Real-Time Traffic Monitoring System using Web-based GIS and Multimedia Technology

● Low-Cost, High-Accuracy GPS Positioning System Utilising Multiple Reference Station Network

Structures

● Behaviour of an Interlocking Steel Beam● Analysis of Tubular T-Joint Under Combined

Axial and Bending Loading ● Nonlinear Dynamic Response Analysis and

Damage Assessment of RC Structures to Blasting Ground Motion

● Behaviour of Full-Scale Lightly Reinforced Concrete Beam-Column Joints

● Ground Motions Recorded in Singapore during the Bengkulu, Sumatra Earthquake (Ms = 8.0) on 5 June 2000

● Adaptive Surface Mesh Generation● Detection of Cracks Through Changes of

Vibration Frequencies● Structural Health Monitoring using Smart

Materials

Transportation

● 'Left Turn On Red' Traffic Scheme in Singaporey

● Modelling of Driver Perception-Response Times at Signalised Junctions

● Spatial Analysis and Modelling of Transport Demand

Water

● Dispersion of a Turbulent Circular Wall Jet● Prediction of Transition in Oscillatory

Boundary Layers by k- Model● Turbulence Characteristic of Flow over an

Abrupt Change in Bed Roughness● Alluvial Bed Resistance and Mean Flow

Velocity in Flumes and Natural Channels● Feasibility of Utilising Reclaimed Lands in

Singapore as Groundwater Source● Effect of Urbanisation Sequence on Flood

Peak Increase of an Overland Plane



The following Conferences, Seminars and Short Courses were conducted by the various Research Centres during the period under review :

Centre for Advanced Construction Studies (CACS) ● Seminar on Management of Large Scale Construction by Prof Dennis Ballou & A/P Lim Ewe Chye in July 1999

● Seminar on Challenges in Construction Technology & Management in September 1999

● Seminar on Behaviour of Structural Materials under Fire Conditions in October 1999 by Dr David Moore, A/P Tan Kang Hai and Mr Toh Wee Siang

● Seminar on Project Management in Practice in February 2000, attended by 115 participants

● Seminar on Design and Build Contracts in May 2000, attended by some 70 participants. The Seminar was chaired by Mr Dennis Ong Chin Lock, Principal HCE Engineers Partnership, and A/P Lim Ewe Chye. Speakers included Prof (Adjunct) Wong Yui Cheong and Prof (Adjunct) Tan Ee Peng, Mr Tan Kian Huay of Obayashi Singapore and A/P (Adjunct) Goh Phai Cheng

Geotechnical Research Centre (GRC) ● Third GRC (Geotechnical Research Centre) Lecture entitled Can Lime/Cement Columns be used in Singapore and Southeast Asia was delivered by Professor Bengt B. Broms on 19 November 1999, and attended by more than 200 practising engineers and researchers. In the lecture, Prof Broms gave a comprehensive review of the applications of lime, lime/cement and cement columns in this region and around the world

● Seminar co-organised with the HDB, Econ International Ltd and China National Water Resources & Hydropower Engineering Corporation (S) Pte Ltd, on Applications of a New Vacuum Pre-loading Techniques for Reclamation using Mud and other Soil Improvement Works in March 2000. The speaker was Mr Lian Daren, Chief Engineer, Tianjin Water Conservancy Bureau China, and the Seminar attracted 130 participants

● Seminar co-organised with ICE & Far East Pte Ltd on Vibratory Driving : Sustainable Approach to Pile Design in March 2000. The presenter was Mr Jan Kenkhuis, Geotechnical Support and Business Development Manager, International Construction Equipment, Netherlands





● Asian Conference on Unsaturated Soil : From Theory to Practice in May 2000, with the support of ISSMGE Technical Committee TC6, attracted over130 papers from 41 countires

● Short course on Geotechnical & Geo-Environmental Numerical Modelling in May 2000, presented by Dr J Krahn, Dr S L Barbour and A/P H Rahardjo

● Seminar on Collapsible Soils in May 2000. It was presented by Prof I Jefferson, Prof S L Houston, Prof E E Alonso, Prof Fredlund and Dr Toll

● Seminar on Rainfall Induced Landslides in May 2000. Presenters were A/P H Rahardjo, Prof S L Barbour, Prof D G Fredlund, A/P Leong E C, Dr D Toll and Mr C N Quan. It was attended by 110 participants

● Seminar on Soil Mechanics - Past and Future in May 2000. Presented by Prof Shen Zhujiang, Department of Geotechnical Engineering, Nanjing Hydraulic Research Institute, China Ministry of Water Resources, it was attended by about 50 participants

● Seminar on Some Experiences with Residual and Volcanic Soils in May 2000 by Dr L D Wesley, University of Auckland, New Zealand, attended by about 50 participants

● Seminar on Designing the World's Largest Underground Cavern : the Gjovik Olympic Ice Hockey Hall in Norway with a Span of 62 m, by Mr P Chryssanthakis, Norwegian Geotechnical Institute, Norway. It was held in May 2000 and about 50 participants attended

Environmental Engineering Research Centre (EERC) ● Seminar on Waste Water Recycling in July 1999 which was sponsored by Hydranautics-Nitto Denko and attended by about 250 participants

● Seminar on Indoor Air Quality in July 1999 by Prof Hildeman from Stanford university and was attended by over 60 participants

● Clean Water Forum in June 2000. Speakers included seven visiting professors from Stanford University, USA, led by Prof James Leckie


http://www.ntu.edu.sg/centre/wwweerc/eerc.htm


Centre for Transportation Studies (CTS) ● GPS/GIS Showcase in November 1999 which featured the products, and services of many industry partners as well as collaborative research efforts between NTU and the University of New South Wales, Australia. This was well attended by professionals from both industry and government agencies such as LTA, HDB, URA, and SISV.

● Two short courses on Urban Transport Planning and Urban Traffic Management & Control, in June 2000. These were attended by transportation professionals from Hong Kong, Malaysia and Singapore.

● Seminar on False Trails and Real Solutions to the Metal Fatigue Problem in June 2000 by Prof. Keith Miller, University of Sheffield, UK.

● Seminar on Value of a Statistical Life in a Road Accident Context: Stated Preference Allowing Interactions and Quadratic Effects in July 2000 by Prof. Juan de Dios Ortúzar, Department of Transport Engineering, Pontificia Universidad Católica de Chile, Chile.

A/P Adrian Law Wing Keung received an Outstanding Technical Paper Award by the Bechtel Corporation, USA, for his paper "Marine Tailings Disposal Simulation" co-authored with Dr Angelos Findikakis and published in the April 1998 issue of ASCE Journal of Hydraulic Engineering. Bechtel gives out the award each year to a few publications that "contribute to the progress of technologies benefiting the company and their customers."

A/P Zhao Jian was presented the Richard Wolter’s Prize by the International Association of Engineering Geology and the Environment (IAEG) on 8 August 2000, at the 31st International Geological Congress in Rio de Janeiro, Brazil. The Richard Wolter’s Prize is a major IAEG award and is awarded to an individual bi-annually in recognition of his eminent contributions, through research, to the development of engineering geology.




A/P Adrian Law Wing Keung was awarded the 2000 Wesley W. Horner Award for the paper "Wind Mixing in Temperature Simulations for Lakes and Reservoirs" co-authored with Dr Angelos Findikakis and published in the May 1999 issue of ASCE Journal of Environmental Engineering. The award is given annually by the Environmental Engineering Division of the American Society of Civil Engineers " to honour the authors of a paper published by the Society dealing with hydrology, urban drainage, or sewerage, that makes the most valuable contribution to the environmental engineering profession". It was presented in July 2000 during an award luncheon in the ASCE Environmental and Pipeline Engineering Conference at Kansas City, Missouri, USA.

A/P Adrian Law Wing Keung (right) with his co-author

after receiving the 2000 Wesley W. Horner Award

A/P Anthony Goh Teck Chee has joined the Editorial Board for The 6th International Conference on the Application of Artificial Intelligence to Civil & Structural Engineering, which will be held in Eisenstadt, Vienna, Austria, from 19-21 September 2001.

Ast/P Show Kuan Yeow delivered a Keynote Paper on “Reuse of incinerator ash - current and future trends” at the International Symposium - Sustainable Construction: Use of Incinerator Ash at the University of Dundee, UK on 20-21 March, 2000. The paper was authored by Show, K. Y., Tay, J. H. and Cheong, H. K.

Prof A Appan, A/P James M W Brownjohn and A/P Yip Woon Kwong received the Merit Award from the Singapore Productivity and Standards Board (PSB) during the World Standards Day 2000.


CSE Research Bulletin No. 14 January 2001

CONSTRUCTION

Seismic Behaviour of Connection betweenPrecast Concrete Beams

Li Bing ([email protected])Yip Woon Kwong ([email protected])Khoo Jyh Hao

The construction industry has long recognised the benefitsof using precast concrete members in the construction ofsimple and complex structures. Precast concreteconstruction can be a very competitive alternative to cast-in-place construction, especially when the speed ofconstruction is a primary concern. Besides constructionspeed, precast concrete construction possesses many otheradvantages; one of them is the high quality product thatcan be obtained as prefabrication is done in almost idealfactory-constructed conditions; the product is constructedaccurately, and has excellent durability and goodaesthetics. Another advantage of precast concrete is thereduction in the use of site formwork.

Connection design is one of the most importantconsiderations for the successful application of precastconcrete technology to achieve buildability. The designand detailing of the connection affect its strength, ductilityand stability, as well as the load redistribution of thebuilding. Nevertheless, much attention has been dedicatedto the design of individual components, leaving theconnection details for consideration only after the wholestructural concept has been adopted.

In the past, many precast concrete structures that weredesigned for lateral load resistance have shown distress asa result of inadequate attention to connection design.However, in a region of low seismic risk and low windspeed, such as Singapore, it is a feasible option to designprecast concrete systems as the primary lateral load-resisting frame. For higher confidence in application,precast concrete moment-resisting frame systems requireadditional design considerations that should be verifiedthrough experimental tests for validation of theirperformance.

An investigation of the behaviour of five moment-resistingframe connections between precast beams is beingconducted at Nanyang Technological University. Theobjective of this research is to study the performance andresponse of connections between precast concrete beamsunder lateral loading. A testing program will be devised toprovide experimental evidence on the seismic behaviour ofproposed precast moment–resisting frames. Five full-scalesubassemblages will be quasi-statically tested to failureunder reverse load conditions with increasingdisplacement to failure. The set-up of the test frame isdepicted in Figure 1.

All five reinforced concrete sub-assemblages are of H-shape, where the precast beam will be connected to theprecast columns in a cast in-situ joint at a distance awayfrom the column face as shown in Figures 2 and 3. Thiswill provide information on the seismic behaviour of

connections connected in a region other than at the beam-ends and at the point of contraflexure.

The first specimen is to be cast as a monolithic structureand will serve as a control specimen. The remaining fourspecimens are separated into precast elements and will beconnected using different proposed detailing as thevariables in this test. The results generated from theprecast structure tests will subsequently be compared tothe one control specimen test. This is expected to result ina better understanding of precast concrete moment-resisting systems.

Figure 1. Test frame in NTU

Figure 2. Reinforcing details of Unit 3

Figure 3. Reinforcing details of Unit 4


Seismic Performance of Reinforced ConcreteFrames under Low Intensity Earthquake Effect

Li Bing ([email protected])Pan Tso-Chien ([email protected])Wu Yiming

IntroductionReinforced concrete frame structures designed andconstructed using the BS 8110 code, exist in many regionsof low to moderate seismic risk. The seismic performanceof gravity load designed reinforced concrete structuresbased on the BS 8110 is still not well understood. In recentyears more attention has been focused on evaluating theseismic performance of the buildings designed to the BS8110 which are now considered to provide inadequateprotection against future possible earthquake. This articlepresents part of the ongoing research at NanyangTechnological University, Singapore that is investigatingthe seismic performance of such types of structures underearthquake action. The investigation involves: designingrepresentative reinforced concrete frame structures;modelling the components of these structures includingpotential non-ductile behaviour of their critical regions;assessing the anticipated seismic demands; and proposingtarget levels of critical region strength and ductility, andpotential retrofit strategies. This article presents resultfrom the first stages of the investigation, a seismicassessment of three typical buildings designed based onBS 8110. A non-linear inelastic analysis was conducted toinvestigate the drift demands of the structures, shear andductility demands of the members and joints under thegiven earthquakes.

The situation in SingaporeA look at a world seismicity map reveals that Singapore isabout 400 km away from a highly active seismic belt alongSumatra Island, Indonesia. Historically, there has been norecord of earthquake damage in Singapore. Although therehas never been any reported earthquake damage toPeninsular Malaysia and Singapore, ground tremors werefelt in the region many times, and the incidents haveincreased significantly in number over the last threedecades. Epicentres of the Sumatra earthquakesresponsible for the tremors felt in Malaysia and Singaporegenerally fall around a circle of 500-km radius centred onSingapore. Based on previous research conducted at NTU,the earthquake risk here in Singapore is not zero.Singapore, like Thailand, Australia, and the eastern part ofthe United States, may be classified as an area with low tomoderate earthquake risk.

Code requirements and Singapore practiceSince Singapore does not experience strong winds, thecritical horizontal load is usually the notional lateral loadspecified by BS 8110. Many buildings are governed by

weak column-strong beam behaviour and possess limitedductility. Under high lateral loads, column hinging, whichcan lead to a soft-story collapse mechanism, is probable,and the margin of safety against collapse is minimal duringlow to moderate level earthquakes. Therefore, thebuildings, which were designed and constructed inSingapore, may not have sufficient lateral strength forresisting possible earthquake attack.

Compared to the seismic design codes, the deficiencies ofreinforced concrete structures designed based on BS 8110are mainly a consequence of the lack of structural ductility.The following features may be distinguished in the typicaldesign of building structures in Singapore:

• Inadequate anchorage of longitudinal reinforcement inbeam-column joint regions and lap splices placed inpotential hinge regions of structural members.

• Inadequate transverse reinforcement in beams andcolumns.

• Inadequate anchorage of transverse reinforcement.• Inadequate shear strength of beam-column joints due

to lack of shear reinforcement.

Structural modelsThree reinforced concrete frames having 3, 6 and 9 storeyswere considered for the present study. These three framesare denoted as 3S, 6S and 9S. The effect of seismic actionwas considered in the N-S direction. The elevation of theinterior frames in this direction is shown for 9S in Figure2. The three frames were designed for combined gravityand lateral loads in accordance with the Singapore LoadingCode, and the their structural members were proportionaland detailed according to BS 8110.

Ground motionsTo form an earthquake data set as input ground motionsfor the designed frames; two ground motions were selectedfrom the earthquake database system at NTU. The 1940 ElCentro record (NS component) and the Bucharest 1977record. These motions, scaled to give a peak groundacceleration of 0.1g, which provides excitation inproportion to the low to moderate seismic risk, were usedto represent rare long-distance earthquake effects.

Results of dynamic analysis

Maximum interstorey drift ratio

Interstorey drift ratio is considered a primary globalperformance parameter. Figure.1 shows the maximuminterstory drift ratios due to El Centro and Bucharestrecords. It should be noted that the maximum interstoreydrifts due to the Bucharest record were significantly largerthan those due to the El Centro record.


Figure 1. Maximum interstorey drift ratio of the framesdue to the El-Centro and Bucharest records

Rotational ductility demands at member levels

Rotational ductility is defined as the ratio of the maximumrotation at the end of a member to the yield rotation asfollows:

y

plastic

y θθ

θθµθ +== 1max (1)

In which maxθ and yθ represent the maximum and the

yield rotations at the end of the member. Because theinelastic flexural deformation of a beam is assumed to beconcentrated at the ends of the beam, the plastic rotationsoccur at the plastic hinges.

The rotational ductility demands at each end of theelements were evaluated for the three example structuresdescribed previously. Figures 2 and 3 show thedistributions of the rotational ductility demands for 9Sframe. It can be observed that the inelastic deformations ofall the three frames subjected to the Bucharest earthquakeare widespread at all storey levels. However, in the case ofthe El Centro earthquake, it can be seen that the ductilitydemand due to the El Centro input was much less than thatdue to the Bucharest input.

ConclusionsThe following conclusions can be drawn as a result of theseismic assessment of a reinforced concrete building framedesigned to BS 8110 in Singapore:

1. The critical failure mechanism of the 3-storey framewas a soft-storey mechanism including flexural plastichinges combined with shear failures of the beams andcolumns.

Figure 2. Rotational ductility and joint shear demands dueto the El-Centro record

Figure 3. Rotational ductility and joint shear demands dueto the Bucharest record

2. The critical failure mechanism of the 6 and 9 storeyframe was a mixed mechanism including flexuralplastic hinges combined with shear failures of thebeams and columns. The results of the analysesindicated that the beam plastic hinge behaviour wouldcontrol the inelastic seismic response of the frame.

1

3

5

7

9

0 0.5 1 1.5Story Drift Ratio (%)

Sto

ry L

evel

El-centro

Buch


3. A more critical aspect with respect to shear was foundin the beam-column joints. Relatively large joint shearinput during the low to moderate earthquakesindicated that the joints of the structure could suffersevere diagonal tension cracking and the strength ofthe structure is likely to be governed by joint shearfailure.

4. The reinforced concrete frames designed to BS 8110have a low stiffness due to the inadequatereinforcement details of the structural members andjoints.

5. Further research studies are obviously required tomore fully understand the seismic performance ofbuildings in low and moderate seismic risk regionsand develop appropriate design guidelines.

References:[1] Li Bing and Pan Tso-Chien, "Lessons Learnt from the

Past Disasters – Singapore Perspective", Journal ofIES (Accepted).

[2] Li Bing, Pan T.C and Wu Yiming "SeismicPerformances of Reinforced Concrete Frames underLow Intensity Earthquake Effect", ASD 2000International Conference on Advances in StructuralDynamic, Dec 2000, Hong Kong.


Seismic Resistance of Reinforced ConcreteBeam-Column Joints with Non-ductile Details

Li Bing ([email protected])Pan Tso-Chien ([email protected])Wu Yiming

The beam-column joints are often the weakestlinks in a structural system. Joints are exposedto extreme shear and bond demand and thetypical congestion of reinforcement barsfurther worsens the situation. It is thereforenecessary to provide strong horizontalconfining reinforcement within the joint zone.In BS 8110, no detailing requirement for beam-column joints is specified.

Having realised the importance of beam-columnjoints in reinforced concrete structures,extensive worldwide research has beenundertaken during the past thirty years toinvestigate the behaviour of beam-columnjoints both under monotonic loading andsimulated seismic loading. Most of thesestudies have focused on ductile beam-columnjoints usually in areas of high seismicity.

The potential risk of damage to reinforcedconcrete buildings from a moderate earthquakein regions of low to moderate seismicity isbecoming a matter of growing concern to thepracticing engineering community. However,only limited experimental results are availableon the seismic performance of beam-columnjoints in zones of low seismicity.

Buildings in such zones are typically designedonly for gravity loads according to the non-seismic detailing provisions of a code such asBS 8110. Although such structures aredesigned without consideration of lateral loads,they still possess an inherent lateral strength,which may be capable of resisting some minorand moderate earthquakes. However, poordetailing of members can lead to inadequatestructural performance during seismic activity.

The aim of this study was to examine thebehaviour of beam-column joints with“nonductile” or "limited ductility" details underseismic loading and the influence of jointbehaviour on the global behaviour of the wholeframe. The experimental component of thisinvestigation focused on the response ofinterior beam-column connections subjected tolateral earthquake-type loading.

Four interior beam-to-column sub-assemblageswere tested under quasi-static cyclic loading atNTU (see Figures 1 and 2). The effect of limitedductile details in the beam-column joints wasfound to be significant. The experimentalresults indicated that the beam-column jointswith non-ductile details failed at a low demandof ductility, and the total energy consumptionwas very low (see Figure 3). Such beam-columnjoints with nonductile details are a critical partof a building during a low to moderateearthquake attack.

Figure 1. A unit in the test rig

Figure 2. Observed cracking of Unit 1

Figure 3. Story shear force verses story drift,Unit 1


Strengthening of One-way Slabs UsingCarbon Fibre Plates: The Effect ofPreload

Chan Toong Khuan ([email protected])Niall MacAlevey ([email protected])

IntroductionThis article is concerned with the use ofcarbon fibre reinforced plastic (CFRP)plates to strengthen one-way spanningslabs to increase their flexural capacity. Inpractice, the CFRP plates may have to beaffixed to existing members, which mayhave existing cracks. Therefore it isnecessary to study the effect of preload(i.e., the effect of existing cracks) on theperformance of a strengthened member.

SpecimensA total of nine slab specimens were castfor this project to investigate threeparameters: steel ratio, pre-loading, andlength of CFRP plate. The specimens were330 mm wide, 100 mm thick and 2.7 mlong and designed as one-way spanningslabs to carry two point loads at one-thirdspan. Two specimens without any CFRPplates acted as controls. Six specimenswere utilised to study the effects of pre-loading before the CFRP plates wereattached. The final specimen had a fulllength CFRP plate to assess the effect oftaking the plates beyond the supports.

Figure 1. Cross section

Figure 2. Test set-up of slab specimens

To ensure flexural failure, all thespecimens were designed to have a highershear capacity than the minimum requiredfor flexural failure. Details of thespecimens are shown in Table 1.

Strain gauges were attached to the steelreinforcements, concrete compression faceand CFRP plates.

MaterialsThe CFRP plates were 50 mm wide and1.2 mm thick. Three samples of the plateswere tested and the material was observedto be elastic up to failure at a stress of2940MPa. The modulus of elasticity was165 GPa. The plates were attached to theconcrete slabs with a two-part cold-cureepoxy. Results from cube tests carried outon the week of the bending tests indicatethat the cube crushing strength wasapproximately 67 MPa. Welded steelmeshes of 6 mm and 8 mm were used asreinforcement. Mean proof stress of677 MPa and 653 MPa was measured forthe 6 mm and the 8 mm, wiresrespectively.

Test ProcedureThe control specimens were tested first todetermine the ultimate moment resistancefor the reinforced concrete section. Thisvalue was used to determine the load forthe pre-loaded specimens. Two pre-loadlevels were considered: loads of 60% and80% of the ultimate load. The pre-loadingwas carried out after a period of curing ofat least 28 days. The load was applied inincrements of 1 kN and readings of crackwidth and deflection recorded. The soffit

100

CFRP

330

76

2500

850 850800P/2 P/2


of the specimen was abraded gently with aneedle gun to roughen the surface and wascleaned with compressed air. The CFRPplates were bonded to the soffit of thespecimens with epoxy adhesive and left tocure for another 14 days.

The deflection of the specimen wasmeasured with displacement transducersand the crack widths were measuredvisually with magnifying scales.

ResultsThe control beams failed at loads predictedby assuming that the concrete reached itscrushing strain and the steel reinforcementyielded. All the CFRP strengthenedspecimens exhibited large increases in loadcarrying capacity ranging from 60% to140%. These large increases were due tothe relatively light reinforcement in theslabs utilising only a small section of theconcrete in compression. The addition ofthe CFRP provided for a larger tensionforce with a consequential increase inbending capacity. (See Table 1).

Figure 3. Typical results

There was no significant difference in theload carrying capacity for slabs with and

without preload although the deflectionswere higher in the specimens with preload.This observation deviates from test resultsreported by Tan and Mathivoli [1] andArduini and Nanni [2] which noted thatthere was a drop in ultimate capacity dueto preload.

The residual deformation after theapplication and removal of preload wasapproximately 8-10 mm for 60% and12 mm for 80% preload, respectively. Thefailure mode of all the CFRP strengthenedslabs was delamination which initiatedfrom the midspan of the slab andpropagated through the entire length of theplate and caused complete loss of bond atthe concrete-epoxy interface. In all casesthe strains in the CFRP plates weremeasured to be approximately 0.006 at theload corresponding to delamination.Khalifa et.al. [3] have reported a similarlimiting strain in investigations on shearstrengthening of concrete beams with FRPplates.

The crack width of the S6 control beamwas 0.4 mm at a working load (taken as60% of the ultimate load). Thecorresponding crack width of the CFRPstrengthened slabs at a similar load of7.8 kN was reduced to 0.1 mm.

The CFRP strengthened members whichwere preloaded showed wider crackscompared to the members which were notpreloaded. The existing cracks in thesespecimens widened as the load wasapplied. No new cracks were observeduntil the load exceeded the precrackingforce, after which a number of new cracksappeared at a regular spacing of 100 mm.Specimen S6-50-1, which was preloadedto 7.8 kN had a maximum crack width of0.4 mm at 18.3 kN: approximately 60% ofthe ultimate load of the strengthenedsection. Specimen S6-50-2, which waspreloaded to 10.4 kN exhibited smallercrack widths as compared to the specimenwhich was not preloaded.

Load vs. Midspan Deflection

05

1015202530354045

0 20 40 60 80 100

Deflection (mm)

Load

(kN

)

With CFRP

No CFRP


ConclusionsThe addition of CFRP plates maysubstantially increase the flexural capacityof lightly reinforced slabs. However, theload-deflection behaviour becomes brittle.The level of preload (i.e., the presence ofexisting cracks) did not have any effect onthe ultimate capacity of the strengthenedslabs.

Significant improvement in the crackingbehaviour can be achieved with theaddition of CFRP plates.Providing full length plates (specimen S8-50-0F) seems to have little effect on thefailure load.

References[1] Tan, K.H. & Mathivoli, M., Behaviour

of precracked RC beams externallybonded with carbon fibre sheets,Proceedings of the Third InternationalSymposium on Non-metallic (FRP)reinforcement for concrete structures,Vol.1, Oct 1997, Sapporo, Japan,pp.271-278

[2] Arduini, M. & Nanni, A., Behaviour ofprecracked RC beams strengthenedwith carbon FRP sheets, Journal ofComposites for Construction, Vol.1,No.2, May 1997, pp.63-70

[3] Khalifa, A., Gold, W.J., Nanni, A. &Abdel Aziz, M.I., Contribution ofexternally bonded FRP to shearcapacity of RC flexural members,Journal of Composites forConstruction, Vol.2, No.4, Nov 1998,pp.195-202

Table 1. Specimen details and failure loads

Specimen Steel CFRP Preload(kN)

Fail(kN)

S6 4T6 None None 12.9S6-50-0 4T6 50x1.2 None 29.8S6-50-1 4T6 50x1.2 7.8 30.9S6-50-2 4T6 50x1.2 10.4 29.9

S8 4T8 None None 20.9S8-50-0 4T8 50x1.2 None 35.8S8-50-1 4T8 50x1.2 12.5 41.1S8-50-2 4T8 50x1.2 16.7 34.2S8-50-0F 4T8 50x1.2 None 32.9

Table 2. Increases in load carryingcapacity

Specimen Load ratio overcontrol beam

Failure mode

S6 - Steel yieldS6-50-0 2.30 DelaminationS6-50-1 2.38 DelaminationS6-50-2 2.31 Delamination

S8 - Steel yieldS8-50-0 1.72 DelaminationS8-50-1 1.97 DelaminationS8-50-2 1.64 DelaminationS8-50-0F 1.58 DelaminationS8-50-0F 1.58 Delamination


Behaviour of Mortar under Tri-axial Stress

Tan Teng Hooi ([email protected])

Introduction and purposeResults of tri-axial tests on concrete provide structural designers with data regarding thebehaviour of concrete under complex states of stress. The failure mechanism of concreteappears to be closely related to the behaviour of cement mortar. As part of an effort tounderstand the origins of this behavioural pattern, the present work is concerned with thederivation of an analytical description of the strength and deformational response of cementmortar under tri-axial monotonic loading.

Tri-axial experimentsTri-axial tests were performed on cement mortar and concrete cylinders (100mm diameter and200mm height) subjected to a constant confining oil pressure together with an axial load,which was increased until failure. Four groups of cement mortar, G30, G40, G65 and G90 andtwo groups of concrete, G40 and G50 were tested. The concrete specimens were based on theG40 mortar mix but with different amounts of coarse aggregates.

Results and discussionIn this study, each stress and strain state was resolved into a hydrostatic and a deviatoriccomponent, and the characteristic feature of the analysis was based on the assumption that thenonlinear material behaviour was dictated by internal fracture processes. The analyticalformulation for cement mortar was derived from the experimental tri-axial strength anddeformation data. The proposed failure envelope for mortar was compared with concrete(Kotsovos) in Figure 1. These two failure envelope were very close at low hydrostatic stress,but they departed from each other with the increase in the state of confinement. The failureenvelope for mortar was lower than that for concrete. In other words, the increase in strengthfrom confinement was less.

The stress-strain relationships for mortar and concrete are shown in Figure 2. The brittlebehaviour of mortar was modified by the introduction of coarse aggregates. The strength andaxial stiffness were enhanced. The effect was greater for larger amounts of aggregates. Asimilar trend is reflected in the deviatoric behaviour (Figure 3): the concrete has less sheardeformation for the same shear stress. The aggregates reduced the amount of cracking thatleads to shape change and eventual failure. As for the volume change, the bulk modulus wasalso higher for concrete than mortar owing to the presence of the (stiffer) aggregates. Hence,the change in volume for mortar was greater for the same hydrostatic stress (Figure 4).

The difference in the cracking mechanism for mortar and concrete has been determined in thisstudy. From the test results, the constitutive model to describe the failure and deformationalbehaviour of mortar has been developed and it gives a close prediction for the properties ofmortar under triaxial stress.


Confining Stress Normalized with Uniaxial Strength

σ2 / fc

Figure 1. Comparison of test results with the proposed failureenvelope for cement mortar and concrete

0.0 0.2 0.4 0.6 0.8

Axi

al S

tres

s N

orm

aliz

ed w

ith

Uni

axia

l Str

engt

h

σ 1/ f

c

0

1

2

3

4

fc=28.27 MPa

fc=38.13 MPa

fc=66.44 MPa

fc=92.96 MPa

Proposed Ultimate Failure

Envelope for MortarFailure Envelope for

Concrete (Kotsovos)

Radial Strain ε2 Axial Strain ε

1 (mm/m)

Figure 2. Comparison of stress-strain relationship between mortar andconcrete at the same confining ratio σ2 / fc = 0.1

-8 -6 -4 -2 0 2 4 6 8 10

Axi

al S

tres

sσ

1 (

MP

a)

0

20

40

60

80

100

G40 MortarGC40 ConcreteGC50 Concrete

(mm/m)


Deviatoric Strain γο (mm/m)

Figure 3. Comparison of deviatoric stress-deviatoric strain relationship for cement mortar and concrete

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Dev

iato

ric

Stre

ssτ

o

(MP

a)

0

5

10

15

20

25

30

35

40

45

50

55

GC50ConcreteGC40G40A Cement

Volumetric Strain εο (mm/m)

Figure 4. Comparison of hydrostatic stress-volumetric strain relationship before OUFP for cement mortar and concrete

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Hyd

rost

atic

Str

ess

σ

ο

(MP

a)

0

51015

2025

303540

4550

556065

7075

G40A Cement MortarGC40 ConcreteGC50 Concrete


Testing of Concrete under High Temperature

Tan Teng Hooi ([email protected])Shi Xudong ([email protected])

IntroductionConcrete is a composite material and it contains all three phases: gas, liquid and solid. Whensubjected to heating e.g. in building fires, the strength and deformation behaviour of concrete iscomplex. The behaviour can be better understood by laboratory testing concrete specimens at hightemperature. Recent research shows that the strength and deformation of concrete can besignificantly different for different paths of stress-temperature. Hence, a proper constitutiverelationship of concrete subjected to fire must include the influence of different stress-temperaturepaths. Owing to the advancement in concrete technology, the strength of concrete has increasedgreatly. However, there is not enough information and understanding on the behaviour of highstrength concrete at high temperature. Some published research results have shown that theproperties of high-strength concrete are significantly different from those of normal strengthconcrete.

Test setupEquipment has been set up in the Construction Laboratory at Nanyang Technological University(NTU) to conduct tests on concrete at high temperature. Figure 1 shows this test equipment. Thetest set-up has three components: heating, loading and measuring.

For the heating component, an electric heating furnace is used and it is similar to most other set-upsused for the study of concrete behaviour. An electric furnace normally allows better control ofheating which is necessary to achieve a desired temperature-time curve. The furnace has a heatedchamber of 200 mm diameter by 700 mm high and is meant for testing concrete cylinders of 150mm by 300 mm long. Since concrete can rupture explosively during failure, a metal muffler is usedto protect the fragile electric heating elements. The temperature in the furnace chamber is controlledusing a closed-loop system. The maximum rate of temperature rise is 65°C per minute and thecapacity of the heating element is 1200 °C.

Loading is performed using a closed-loop servo-controlled 2 MN Instron test machine. To allowplacement and positioning of the specimen prior to testing, a special sliding device was speciallymade. Specially shaped cylindrical nickel-based alloy attachments were also designed to transmitload from the compression platens of the test machine to the specimen at high temperature.

Unlike a test at room temperature, measurement of specimen deformation at high temperature isdifficult. Hence, special measuring attachments were designed to connect the specimen deformationto the LVDTs.

Test programmeAs the strength and deformation behaviour of a specimen under high temperature is dependent onthe duration of testing, chamber temperature and temperature distribution in the chamber,temperature distribution in the specimen, etc., the test regimes have to be strictly planned andexecuted. There are three different conditions under which the tests on concrete are carried out:

a) Behaviour under increasing load at a constant temperatureb) Behaviour under increasing temperature under constant stressc) Residual behaviour after heating


Concretes of different strength (ranging from 15 to 106 N/mm2 in cylinder strength) have been usedin the study. So far, tests in category (a) have been conducted. To shorten the duration of testing athigh temperature, specimens were heated in a standard furnace to predetermined temperatures untila uniform temperature distribution inside the sample was achieved before transferring it to the testrig.

Figure 2 shows the effect of temperature on the strength of concrete.

Figures 3 shows the effect of temperature on the stress-strain behaviour of concrete. Generally, astemperature increases, both the stiffness and strength are reduced. However, the concrete becomesmore ductile and the strains at peak stress and at failure increase. From the test results it is veryclear that this test set-up can better meet the testing requirements for an investigation of the strengthand deformation behaviour of different strength grade concrete subjected to different temperatures.

ConclusionsAlthough the test set-up can meet many testing requirements for behaviour investigations ofdifferent strength grade concrete subjected to different temperatures, improvements will beprogressively introduced. Work is underway to have multi-zone heating to produce a more uniformtemperature distribution in the chamber. A very high stiffness machine will also be introduced inthe near future to meet the demands of testing high strength concrete specimens.


insulation blanket

Specimen

elementThermocouple bar

furnaceCeramic fiber

Sliding vehicle

of test machine

Thermocouple wires

Ceramic fiber

Top compression platenof test machine

Top compressionsteel attachment

Electric heating

Electric heatingMuffler

insulation blanket

Bottom compressionDial gage

steel attachment

Bottom compression platen

Figure 1 The sketch of test setup

Figure 2. Compressive strengths of different strength concretes subjected to different temperatures

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 100 200 300 400 500Temperature, C

Rat

io o

f com

pres

sive

str

engt

h at

ele

vate

d te

mpe

ratu

re to

that

at

roo

m te

mpe

ratu

re

AvgG15

AvgG37

AvgG50

AvgG75

AvgG106

G15

G37

G50

G75

G106


Figure 3. Stress-strain curves of different strength concretes subjected to different

temperatures

0

10

20

30

40

50

60

70

0 3 6 9 12 15

Strain x10-3

Stre

ss, M

Pa

G75-030

G75-300

G75-500

G37-030

G37-300

G37-500


ENVIRONMENT

Waste Human Hair as a Renewable Sorbent for Oil-spill Cleanup

J Y Wang ([email protected])J H Tay ([email protected])

Z B Ariffin ([email protected])T T Lim ([email protected])

IntroductionSorption is often used for oil spill cleanup and recovery. At the oil spill scene, sorbents are applied onto theoil slick and are then collected for disposal after the adsorption and/or absorption of the oil has taken place.In some cases, the collected oil is separated from sorbents for further use. The commonly used oil sorbentsinclude sawdust, hay, volcanic ash, polyurethane foams and polyester shavings.

The use of sorbents for oil spill cleanup may encounter some technical problems. For instance, the physicalnature of sorbents like hay does not allow a smooth distribution onto the oil slick. Thus high labour costscan be expected which may cause the total cost to be relatively high though the cost of the material itselfmay be inexpensive. Recovering the mixture of oil and sorbents from the open sea under the influence ofstrong wave and wind conditions has been another challenging issue for oil spill cleanup operators. Further,not all the sorbents available can be used to recover the sorbed oil, i.e., squeezing out the oil from thesorbents for further use. The mixture of oil and sorbents must be disposed of either by burning orlandfilling. Disposal of oil spill waste may have potential impacts on the environment and result insecondary pollution (US EPA, 1974; Mullin, 1997).

Recently, the US National Aeronautics and Space Administration (NASA) announced that its laboratory inAlabama conducted an experiment which shows that human hair can be used as a potential sorbent for oilspill cleanup. The idea was suggested by Mr. McCrory, a hairdresser from Alabama, based on his accidentalfinding that motor oil can be successfully sorbed by human hair. An investigation was initiated at NanyangTechnological University (NTU) to systematically evaluate the feasibility of using waste human hair totackle oil spill cleanup problems.

The objectives of this project were to (1) determine the sorption capability of human hair in terms of itssorption capacity, i.e., pick-up ratio, sorption rate and sorption mechanism and (2) determine the renewablecapacity of human hair after recovery of oil.

Materials and methodologiesFigure 1 shows a 1000X magnification of human hair. The outer layers of the hair shaft comprise flattened,overlapping cuticular “plate-like” cells arranged very much like roof tiles. The centre of the hair shaft is themedulla, which consists of a honeycomb of irregularly shaped areas of keratin with air spaces in between.These unique “plate-like” cells and the medulla may be the significant features that make human hair aneffective sorbent.


Figure 1. A 1000X magnification of human hair.

Two experiments were conducted to determine (1) the maximum pick-up ratio of crude oil on human hair inseawater and (2) the maximum pick-up ratio of crude oil on used human hair in seawater. A pillow of 450mm x 300 mm was made from mosquito netting. The open edges were joined together by weaving fishingline through the holes on the netting. The hair was then stuffed into the pillow. The amount of hair dependson the requirement of each experiment. Care is taken to ensure that the hair is completely packed together.The dimensions of the hair pillow have no bearing on the results of the experiments. Instead, thesedimensions allow slight movement of the pillow on the oil slick so that the surrounding water can beobserved. An acrylic tank with dimensions of 550 mm x 335 mm x 300 mm was chosen as the test tankbecause of its availability and transparency which allows observations of the seawater, crude oil and hairpillow. The test procedures for each of the two experiments are as follows:

Experiment 1: Maximum pick-up ratio of crude oil on human hair in seawaterStep 1: The pillow, hair and collection tray were weighed. The initial weight of the hair used was 200g.Step 2: 7 cm of seawater was poured into the test tank.Step 3: 960 ml of crude oil was poured into tank allowing the oil to cover the entire water surface.Step 4: The hair pillow was placed onto the oil slick.Step 5: After 15 minutes the pillow was transferred form the tank to the collection tray. The weight of the

tray and pillow was measured. This step was repeated for the durations of 30, 45, 75, 105 and 165minutes.

Step 6: After 165 minutes the pillow was wrung out and the crude oil was recovered into the collection tray.Step 7: The wrung pillow was hung to allow the remaining crude oil to drop into the collection tray by

means of gravity. This was continued for about 12 hours.Step 8: The contents of the collection tray was poured into a measuring cylinder allowing the formation of

oil and seawater. The volumes of the oil and seawater were recorded.Step 9: The hair was removed from the pillow and was weighed along with collection tray and pillow.

Experiment 1 was conducted twice with 300g and 400g of hair, respectively. The whole experiment wasrepeated with 580ml, 930ml, 1290ml and 1650ml of crude oil using 300g and 400g hair pillows.


Experiment 2: Maximum pick-up ratio of crude oil on used human hair in seawaterThis experiment was a repetition of Experiment 1 but required the use of used hair from previousexperiments. The hair strands were already laced with oil sorbed from earlier experiments.

Results and analyses Table 1 summarizes the results of Experiment 1. It was observed that as more oil was added, more oil could be sorbed as shownby the pick-up ratios. The weight of oil collected on the hair also dropped as more oil was added. However, the trend changeswith the oil collected in the column, as it increases with the amount of oil added. This shows that more oil could be squeezed outof the hair.

Table 1. Summary of Experiment 1 Results.Wt of oil added, g 500 800 1112 1420Wt of hair added, g 300 400 300 400 300 400 300 400Total oil collected, % 101 136 92 95 73 79 73 83Pick-up ratio 1.68 1.7 2.44 1.9 2.7 2.2 3.45 2.91Theoretical oil wt, % 100 100 100 100 87 80 80 92Recovered oil wt, % 60 104 43 53 36 41 23 30Oil in column, % 41 32 49 43 37 37 50 54

When 500g of oil was added, the pillow had a tendency to sink. This could be due to the competitionbetween the oil and water to be sorbed by the hair. With direct contact between the oil and pillow, the oilclang onto the hair. There was still available adsorption potential by the hair pillow. It allowed the water tobe sorbed after the oil layer thinned out. This may be a contributing factor to the high final effective weightof oil collected at lower weights of oil added. Since water is heavier, it causes the pillow to sink. However,there was no distinct sequence of adsorption between the oil and water. The adsorption in this case wasdependent on which media was in contact first.

Although Table 1 shows that in some cases the total weight of oil collected is more than 100%, this figureactually includes a certain amount of water. This could be confirmed as there was still some traces of oil onthe water surface. However, to simplify the experiment, it was assumed that the amount of water adsorbedby the hair was minimal and could be ignored.

However, a different scenario was observed when 1420g of oil was added. The pillow did not show anytendency to sink at all. This may be due to the first direct contact and adsorption of oil to the pillow. Asthere was then a thicker layer of oil on the water surface, the water had no opportunity come into contact withthe pillow or a rather limited amount was adsorbed. Furthermore, the pillow was constantly floating on theoil layer. The viscosity and high intermolecular forces of the crude oil had the capability of carrying thepillow.

The removal efficiency is also dependent on the intermolecular forces between the oil and the hair pillow. Ifthe forces are stronger, the oil will have a tendency to be attracted to the pillow more than to the test tankwalls. The viscosity of the oil also contributes to this phenomenon. The more viscous the oil, the larger theintermolecular forces between the oil molecules, and also between the oil and hair surface. Therefore, it canbe concluded that the sorption of oil by sorbents may be more effective on high viscosity oils.

The maximum pick-up ratio of 3.45 was calculated without taking into account the oil losses. Thus, thepick-up ratio could have been higher if steps were taken to reduce or prevent these oil losses.


Figure 2 shows the combined graph of adsorption rates versus. time of Experiment 1. The graph illustratesthat the sorbed weights rose quickly during the first 15 minutes, then rose further gradually and finallystabilized when the pillow reached its peak capacity. However, it cannot be confirmed that the adsorption of

Figure 2. Combined graph of adsorption rates versus time of Experiment 1.

oil onto the surface of the hair stopped, as this would be at a microscopic level. The peak adsorption rateincreased with the weight of the hair used. The 400g hair pillow on 1420g of oil showed an outstandingpeak of 74.4g oil/min. The reasons would be similar to the one given for the outstanding adsorbed weight.

The 400g hair pillow in the 1420g of oil experiment indicated an outstanding sorbed weight of 1520g. Thiscould be due to the opportunity available for the oil to be sorbed as the pillow was unable to sink. Thepillow was hence able to sorb more oil.

The mechanism in the adsorption process for Experiment 2 is the same as in the previous experiments. Thepick-up ratio dropped to about 1.08 from 1.7 in Experiment 1, which is about a 35% decrease, using thesame weight of hair and oil. This is attributed to the fact that the oil from previous experiments had alreadycovered the hair surface. Thus, the oil in this experiment could not capitalize on the roof-like surface as theoil was unable to cling onto the crevices. Instead, it depended on the intermolecular forces of the ‘old’ oilthat remained on the hair surface. This may be ineffective especially if the oil was not totally removed fromthe hair, i.e., inefficient recovery from the previous experiments. The peak adsorption rate of the used hairwas also lower, i.e., 46.7g oil/min (See Figure 3) as compared to 74.4 g oil/min when unused hair was takenas the specimen.

Rate of adsorpt ion i ) 1112g i i ) 800g i i i ) 500g i v )1420g o f c rude o i l , 300g and 400g ha i r

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0

Adso rp t i on t ime (m in )

Adso

rptio

n ra

te(g

oil/

min

)

300i 400 i 300ii 400ii 300iii 400iii 300iv 400iv


Rate of Adsorpt ion500g crude oil, 400g used hair

0

46.7

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-10

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0 20 40 6 0 80 1 0 0 120 140 160 180

Adsorpt ion t ime(min)

Rat

e of

Ads

orpt

ion(

g oi

l/min

)

Figure 3. Rate of adsorption vs. time for Experiment 2.

Conclusions

This study has demonstrated that human hair can be used as an alternate, renewable sorbent for oil-waterseparation. The results indicate that human hair can rapidly sorb crude oil in 15 minutes by reaching thepeak pick-up ratio of 3.45 and achieving the outstanding peak sorption rate of 74.4 g of oil per minute.Compared to other natural sorbents, such as hay, human hair uses only ¼ weight equivalent of hay and 1/8 ofthe time required by hay to sorb the spilled oil. The SEM images of the used human hair provided theevidence that, in addition to adsorption, oil sorption processes on human hair may also include absorption.On the other hand, the renewal capacity of the used human hair reached only about 65% of the originalsorption capacity because the hair surface was covered by previous usage. Table 2 compares the sorptionperformance of human hair with some existing commercial sorbents. In general human hair has goodpotential for use as a renewable sorbent for oil spill cleanup and recovery. However, due to the potentiallysevere marine conditions, the use of human hair as a sorbent may be more suitable for small-scale oil spillcleanup or recovery applications. It can also be used as a filter for wastewater treatment to remove oil andgrease.

Table 2. Comparison of Human Hair with Other Sorbents.Sorbent Material Oil Tested Sorbing Capacity

TypeSorbent

Used (kg)Thickness

(cm)Oil

Used (kg)Viscosity

(cs)Test time

(hr)

OilRecovered

(%)

Pick-upRatio

Kraton 1101 11.25 0.64 315 4 24 4 1.1Kraton 1107 11.25 0.64 315 4 24 4.3 1.2Polyurethane – 1 9 0.64 297 6 1 15 5Polyurethane – 2 2.25 0.64 135 6 5 15 46Ekorperl 10.8 0.64 135 6 24 40 5Hay 22.05 0.64 315 6 24 30 4Human hair 0.4 0.70 1.42 16 3 83 4 References[1] Mullin, J. V. (1997). “U.S. Minerals Management Service Oil Spill Research Program.”

Proceedings of the Conference on California and the World Ocean. Part 1, 770 – 780, March 24 –27, 1997, San Diego, CA, USA.

[2] US EPA (1974). Control of Oil and Other Hazardous Materials Training Manual, Office of WaterPrograms, U.S. Environmental Protection Agency, Washington, D.C, USA.


Microbiological Investigations of Aerobic Granules for Enhanced Biological WastewaterTreatmentA M Maszenan ([email protected])J H Tay ([email protected])Y Shan ([email protected])P Shun ([email protected])Q S Liu ([email protected])Stephen T L Tay ([email protected])

IntroductionThe successful operation of the activated sludge process depends on complete degradation of wastematerial and separation of biomass from the supernatant in the clarifier. At a moderate growth rate,filamentous bacteria that are part of the activated sludge microbial community will provide thestructural backbone for particulates to aggregate and form flocs in good settling sludge (Jenkins etal., 1993). However, the outgrowth of filamentous bacteria may upset sludge settling properties.This often results in poor solid-liquid separation and poor quality effluents. In contrast,biogranulation technologies offer an attractive novel process for wastewater treatment, since themicrobial cells are not freely suspended in the bulk liquid as in conventional activated sludgesystems but instead are organized into a consortium of active microbial cells known as granules.These cell aggregates possess high biomass concentration, with the necessary physiologicalcapabilities to degrade the high strength organic waste present in wastewater under high volumetricconversion rates (Beun et al., 1999; Peng et al., 1999). Furthermore, granules exhibit goodsettleability and do not require a separate unit operation for the solid-liquid separation process(Beun et al., 1999; Peng et al., 1999). These properties make granules a suitable matrix for packedbed upflow systems. These compact upflow systems can produce high quality effluents and free upvaluable land space for other high value developments. This is especially important in cities suchas Singapore where land is limited.

Results and discussionTwo types of aerobic granules were obtained from two different sequencing batch reactors (SBR)designated as Reactor 1 and Reactor 2. Both reactors were inoculated with an acclimatised activatedsludge from a municipal wastewater treatment plant treating both industrial and domesticwastewater. Reactor 1 was fed with glucose (1400 mg/l) as the carbon source and operated underhigh COD loading rate with a short hydraulic retention time and high shear force. The granulesfrom Reactor 1 ranged from 1.8 mm to 5.0mm in diameter, and four distinct growth stages wereobserved (Figure 1). Reactor 2 utilised acetic acid as the carbon source and operated under lowCOD loading rate with a long hydraulic retention time and low shear force. The granules fromReactor 2 were generally smaller in size than those from Reactor 1 and ranged from 0.9 mm to 3.0mm in diameter. Three distinct growth stages were observed (Figure 2). Microscopy imagingrevealed that the bacteria in Reactor 1’s granules were predominantly filamentous bacteria, whilethose in Reactor 2’s granules were mostly rods and cocci (Figure 3).

References[1] Beun J.J., Hendriks A., van Loosdrecht M. C. M., Morgenroth E., Wilderer P. A. and

Heijnen J. J. (1999). Aerobic granulation in a sequencing batch reactor. Wat. Res. 33, 2283-2290

[2] Jenkins D., Richard M. G. and Daigger C. T. (1993). Manual on the Causes and Control ofActivated Sludge Bulking and Foaming, 2nd Edition, Lewis Publishers, Chelsea, Michigan.


[3] Peng D. C., Nicolas B., Jean-Philippe D and Rene M. (1999). Aerobic granular sludge-Acase report. Water Res. 33, 890-893

Figure 1. Four growth stages of granules from Reactor 1. (A) Young granules. (B) Mature granules. (C) Old granules with black cores. (D) Disintegrated granules

Figure 2. Three growth stages of granules from Reactor 2. (A) Young granules. (B) Maturegranules. (C) Old granules


Figure 3. Microscopy imaging of granules. Stereomicroscope (A), Gram Stain (B) and scanningelectron microscope (C) images of filamentous granules from Reactor 1. Stereomicroscope (D),Gram Stain (E) and scanning electron microscope (F) images of non-filamentous granules from

Reactor 2


Converting Industrial Sludge-Marine Clay Mixes into Aggregates for Concrete

J H Tay ([email protected])K Y Show ([email protected])S Y Hong ([email protected])

IntroductionIn Singapore, existing landfills are being exhausted faster than the development of new sites dueto the rapid industrialisation and urbanisation that lead to a steep increase in waste generation.The scarcity of land has resulted in high costs for landfilling. Besides land limitation problems,waste disposal through landfilling also raises health and environmental issues. The developmentof a viable alternative, which involves converting waste into useful products, would alleviate theproblem of disposal and at the same time slow down the depletion of the natural resources. Thereuse of waste as building and construction materials is an effective option for wastemanagement and minimisation.

This study used industrial sludge with dredged marine clay for making aggregate materials. Thestudy adopted the approach of waste-to-waste encapsulation and stabilisation, aiming at usingboth industrial sludge and marine clay for the production of coarse aggregates for use inconcrete.

Materials and methodsThe moisture content of the materials was inconsistent when received. Therefore, the materialswere dried in an oven at a temperature of 105oC to achieve a consistent dryness and ground toparticle sizes finer than 80 µm to promote agglomeration for ease of pelletising. The pulverisedsludge and marine clay were combined at different mix proportions with the clay content being0%, 20%, 50%, 80% and 100% by mass. The appropriate amount of water to provide theoptimal water content for moulding was then added to each different mix to form a malleablepaste. The mixtures were then rolled into pellets of sizes between 11 to 15 mm and dried in anoven at a temperature of 105oC before being fired in a muffle furnace at 1135oC. The firingtemperature was maintained at 500oC for a duration of one hour to boost organic removal andalleviate bloating and kept at 900oC for another hour to ensure complete oxidation in order toprevent the development of black core. After firing, the aggregates were tested for theirproperties and their performances in concrete.

The concrete was cast with copper slag grit as fine aggregates, ordinary portland cement as thebinder, and sintered aggregate or granite as coarse aggregates, with a water-cement ratio of 0.5.The concrete samples were tested after 28 days of curing under standard laboratory conditions.The compressive strength was taken from an average of three specimens.

Results and discussionThe aggregates were made in five different compositions, with clay making up 0, 20, 50, 80 and100 % by weight and the remaining consisting of sludge. The optimal mixing water ratios for 0,20, 50, 80 and 100 % clay content were determined to be 35, 39, 42, 42 and 41 %, respectively.At the optimal water ratio, the mixes achieved the maximum dry density and provided a smoothsurface finish with minimal cracks. The materials were then pelletised at the optimal water ratiofor each corresponding mix.

The sintered aggregates were fused and uniformly fired. Comparisons of the properties of theaggregates of 0, 20, 50, 80 and 100 % clay content are shown in Figure 1. The sintered sludge


pellets with 0 % clay had a specific gravity of 3.25, which was more than 20% higher than thetypical value of 2.63 for granite stones. The specific gravity decreased gradually to 3.08, 2.99,2.69 and 2.46 as the clay content increased from 20, 50, 80 and 100 %, respectively, as shown inFigure 1 (a). The addition of marine clay lowered the specific gravity of the sintered aggregatesbecause marine clay has a lower particle density compared to sludge.

The range of particle densities for the sludge-clay aggregates was lower compared with that of2.56 g/cm3 for granite. The particle densities of aggregates are depicted in Figure 1 (b). Theparticle density of the aggregates initially decreased from 2.25 g/cm3 at 0 % clay to a minimumof 1.48 g/cm3 at 50 % clay and then increased to 1.77 g/cm3 at 100 % clay.

The low iron content of the clay material may explain the change in particle density. Thepresence of a high amount of metallic compounds in the industrial sludge tends to impede therelease of gases as the metallic compound melts, resulting in high porosity of the aggregates.The addition of clay which contains a higher amount of organic matter increases the quantity ofgases evolved during sintering, thereby reducing the density of the aggregates. However, withthe reduction of sludge in the mix, the content of metallic compounds decreases, henceproducing aggregates with earthy texture that are less effective in retaining the gasses. Thisincreases the density of the aggregate particles.

The porosity of pellets made from 0, 20, 50, 80 and 100 % clay are 30.8, 40.26, 50.5, 38.7 and28.1 %, respectively as shown in Figure 1 (c). The sludge-clay pellets have higher porositycompared to that of 2.66% for granite. The sludge clay pellets have water adsorption valuesranging from 0.36 to 2.80 %, as shown in Figure 1 (d), while granite aggregate has a wateradsorption value of 1.02 %. The sintered sludge, consisting mainly of fused metalliccompounds, has a poor affinity for moisture. The water absorption remained relatively lowdespite the high porosity, as the impervious skin layer of the pellets restricts the ingress of water.

The aggregate strengths were assessed using the aggregate impact test, which measures thesusceptibility to impact of aggregates. A lower value denotes a better strength. Results plottedin Figure 2 indicate an increase in susceptibility to impact with increasing clay content. Thesintered pellets of up to 50 % clay content displayed better aggregate impact values (AIV) of19.9 to 26.3 % as compared to that of 28.3 % for the granite aggregates under dry conditions.All pellets exhibited a better AIV of between 18.1 to 27.3 % over that of 38.9 for graniteaggregates under wet conditions.

The 28-day concrete compressive strengths of the aggregates were 38.5, 35.5, 31.0, 31.0 and32.5 N/mm2 as shown in Table 1. The 0 % clay aggregate yielded a 28-day concrete compressivestrength of 38.5 N/mm2, which is comparable to that of the granite aggregate of 38.0 N/mm2.The 28-day compressive strength of the concrete decreased as the proportion of clay in theaggregates was increased from 0 to 80 % clay content, before the strength increased again to 32N/mm2 at 100 % clay proportion. The increase in clay content reduces aggregate strength, butimproves the surface texture, providing a better aggregate-cement bond strength, giving rise toan increase in the concrete strength at 100% clay proportion. The improvement in surfacetexture in turn provides a good bond strength that has some degree of influence over thecompressive strength.

ConclusionIt was observed from the results that the increase in clay content lowered the resistance to theimpact of the aggregates. The sintered aggregates have aggregate impact values (AIV) ranging


from 18.1 to 30.4 %, which are comparable to those of granite ranging from 28.3 to 38.9 %. Thesludge-clay pellets of all mix proportions are suitable for use in concrete for both normal andsurface-wearing purposes, except for the 100% clay aggregate. The AIV of 100% clay aggregateexceeded the surface-wearing concrete by a marginal 0.4 %, and is thus only suitable for normalconcrete application.

The 28th day compressive strength of concrete cast with the sintered aggregates ranged from 31to 38.5 N/mm2, which is within the strength requirement of 20 to 40 N/mm2 for structural gradeconcrete. Pellets of 100 % sludge displayed a good concrete compressive strength equivalent tothat of normal granite concrete. The 0 % clay aggregates would be the most suitable forcomplete replacement of granite stones in concrete, as it provides the highest strength to weightratio. In the case of co-disposal with marine clay, the 20 % clay pellets could be used in place ofthe 0 % clay pellets, with a compromise of 8 % reduction in the concrete compressive strength.The 100 % clay pellets could also be used with a compromise of 16 % strength reduction, whenmarine clay requires rapid disposal.

Table 1. Concrete compressive strength

Clay content of concrete aggregates (%) GraniteAggregates

0 20 50 80 100 Stones

Compressivestrength (N/mm2)

38.5 35.5 31.0 31.0 32.5 38.0


0.00

0.50

1.00

1.50

2.00

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3.50Sp

ecifi

c G

ravi

ty .

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sity

g/c

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3.00

0 20 50 80 100Clay Content %

Wat

er A

bsor

ptio

n %

Figure 1. Effects of clay content on various properties of the sintered palletised aggregates

(a)

(b)

(c)

(d)


0

5

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25

30

35

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0 20 50 80 100

Clay Content %

Agg

rega

te Im

pact

Val

ue %

dry condition

wet condition

Figure 2. Influence of mix proportion on Aggregate Impact Value

CSE Research Bulletin No. 14 January 2001Oxidative Bacterial Destruction using MPCO Prior to RO Desalination

Darren D.Sun ( [email protected])J. H. Tay ([email protected])

K. M. Tan ([email protected])

IntroductionDesalination of seawater using reverse osmosis (RO) membrane technology is an alternative solution forpotable water supply. However, the existence of contaminants in seawater, such as suspended solids,colloids, non-biodegradable organic compounds and particularly bacteria, creates a significant bio-foulingproblem on the RO membrane surface. The presence of such contaminants could seriously affect the use ofRO membrane in terms of cost. On the other hand, increasing appearance of microorganisms in drinkingwater has raised concerns about their systemic effects on human health. Particularly, there are concernsabout the possible long-term effects of systemic exposure to certain classes of toxins, for instance the releaseof endotoxin from Escherichia Coliforms upon cell lysis. The increasing concern about pathogenic relatedwater diseases has promoted the implementation of more stringent standards on microbiological pollution ofwater to adequately meet existing requirements of drinking water for better public health.

In order to remove these contaminants, particularly bacteria, a cost-effective pre-treatment process isnecessary prior to the RO membrane process. Membrane photo catalytic oxidation (MPCO) exhibits promiseas a novel technology for the removal of bacteria from seawater. The application of the MPCO processinvolves a cleaning reaction process for further improvement of RO membrane efficiency and drinkingwater quality. In this study, the possibility of complete destruction of E.Coli was examined. TiO 2 as acatalyst was applied into the MPCO reactor to procure an appropriate rate equation for the process.

Material and methodologyMembrane Photo Catalytic Oxidation Reactor: The annular MPCO was equipped with an exteriorcylindrical Pyrex sheath (ID. 5.5 cm; Height 21 cm) fitted with a membrane for the separation of the catalystand water, an air diffuser for the mixtures of gas oxygen and nitrogen, and a UV lamp shielded with a quartzsleeve. The reactor volume was 250 ml. A low-pressure mercury lamp (11W) with major emission at 253.7nm was suspended vertically in the middle of the reactor. A masterflex peristaltic pump was used atcontrolled flow rates for the desired hydraulic retention times (HRTs) of influent. The solution containingphotocatalyst TiO 2 and E.Coli suspensions was placed between the quartz sleeve and the Pyrex sheath. Anair mixture of gaseous O2 and N2 in different ratios was bubbled upwards through the gas diffuser. Thesterility of the solution mixture was ensured by autoclaving at 121 °C for 30 minutes. The E.Coli cultures inLuria Bertani (LB) media were centrifuged before transferring them into the autoclaved mixture in theflasks. The E.Coli suspension was maintained through continuous stirring of the slurry during theexperiments.

Organism Growth Conditions: E.Coli strain J 109 was used as a model bacterium for this study. Thecultures were grown aerobically in LB media containing 10g/l Tryptone Peptone, 5g/l Bacto Yeast extractand 5g/l NaCl. The number of viable cells was determined by plating appropriate dilution onto the LB platesand counting colonies after 24 hours incubation at 25 °C. Three replicate plates were used and the resultswere reproducible with an average relative error of 10 %. Quality control and assurance guidelines describedin the Standard Methods (APHA, 1992) were strictly followed.

Results and discussionFigure 1 shows the proportion of E.Coli colony forming units (CFU) remaining over HRT in the absence ofthe photocatalyst, UV light and in the presence of both factors under MPCO reactions. The result of the darkreaction control run did not show any significant bactericidal activity (less than 1.5 %). This indicates thatthe dependency of MPCO rates on light is crucial. Upon irradiation with light of appropriate energy, thephoto-initiated holes (h+

vb) in the valence band and the excited electrons (e-cb) in the conduction band of

semiconductor TiO 2 may migrate to the irradiated TiO 2 surface to act as active sites by initiating or


participating in oxidation reactions with species in the solution. This hypothesis is supported by the observedbetter overall quantum efficiency of MPCO at longer HRT under uniform light intensity. It was also clearthat the initial removal rate was enhanced to 0.030333 sec –1 from 0.023833 sec –1 under the MPCO processas compared to the UV inactivation in 30 seconds of HRT. An exponential decrease in remaining E.ColiCFU with HRT is observed in Figure 1, suggesting that pseudo-first-order kinetics may be followed underMPCO conditions. As can be seen in Figure 2, the log transformation of the MPCO process of E.Coliconfirms that the pseudo-first-order kinetics is followed closely. The reaction rate of MPCO increases withthe DO content up to 21.34 mg/l with a first-order rate coefficient of 0.053 sec –1. DO is stronglyelectrophilic and thus increasing the DO content would probably reduce the unfavourable electron-holerecombination rate, which in turn improves the overall quantum-yield efficiency of MPCO. Hence, theoxygen level up to 21.34 mg/l was able to maintain the favourable charge balance necessary for the MPCOoxidation process.

At the steady state of MPCO reaction, the E.Coli mass balance of the system can be clearly illustrated in thefollowing equations, taking into consideration the first-order kinetic of MPCO reaction supported by theexperimental results:

QCo + VR = QC + VdtdC

(1)

According to the experimental results from Figures 2 and 3, the pseudo-first-order kinetic should take thefollowing form:

kCdtdC

=− or R = -kC (2)

From the definition,HRT = V/Q (sec) (3)

Equations (1), (2) and (3) could be combined and further rearranged as:

∫∫ =+−

tC

Co HRTdt

CkHRTCodC

0)*1((4)

HRTt

CkHRTCoCokHRT

kHRT=

+−−

+ )*1(**

ln)*1(

1(5)

Equation (5) was derived from the integration of Equation (4).

In the above Eqtions, Co is the initial concentration of E.Coli, CFU/ml, Q is the feed flow rate, ml/sec, V isthe volume of the MPCO reactor, 250 ml, R is the MPCO reaction rate of E.Coli, CFU/ml.sec, t is theMPCO reaction time, sec, C is the concentration of E.Coli at effluent exit at time t, CFU/ml, and k is thepseudo-first-order rate constant from the log transformation, sec –1.

An empirical model could be set-up from Equation (5) and the optimal k value of 0.053 sec –1 from Figure 2based on the role of DO. A fit of the data in Figure 5 to the derived empirical model (Equation (5) with Covariations) yielded a reasonably good agreement with an average correlation coefficient of 0.8911. It can beseen in Figure 4 that the initial removal rate corresponding to 30 second HRT increases significantly as theE.Coli concentration of the influent increases. This may be due to the increase of relative adsorptionavailability on the TiO 2 surface as the probability for surface interaction would increase at highconcentration. Figure 4 also reveals that initial reaction rate could be significantly increased by 2.4 timesfrom the low concentration of 4.90 × 108CFU/ml to a higher concentration level at 1.38 × 109CFU/ml. Theseresults show that the designed MPCO reactor is suitable for removal of high concentrations of E.Coli.


Figures 5 and 6 show the complete cell morphology of E.Coli prior to MPCO reaction and the specimensubjected to MPCO reaction at a HRT of 4 minutes. Obviously, it is possible for the E.Coli cells to be totallydestroyed and converted into other harmless substrates like CO2 and water. Further verification by gaschromatography (GC) and TOC analysis has been done. Direct indication of CO2 evolution from on-line GCanalysis together with TOC mass balance prove that the possibility of the complete photomeneralisationexists in addition to the inhibited respiration.

ConclusionsIn order to remove the bacteria prior to the RO membrane process, a MPCO reaction utilising TiO 2 for thecomplete mineralisation mechanism of E.Coli has been developed in this research work. It was found thatthe ultimate removal efficiency was up to 99% at DO level of 21.34 mg/l, HRT at 60 seconds andconcentration of the bacteria at 109 CFU/ml E.Coli. Experimental results indicate that the reaction rate couldbe characterised by a pseudo-first order kinetic behaviour. The SEM results revealed that the E.Coli wasdestroyed and eventually mineralised into harmless by-products like CO2 and H2O.


0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 10 20 30 40 50 60 70

HRTs (sec)

C / C

o TiO2 without UV

UV without TiO2

UV + TiO2

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0 10 20 30 40 50 60 70HRTs (sec)

CFU/

mL,

X 1

08

Experimental Co = 1.38E+09 CFU/mL



Model Co = 8.10E+08 CFU/mL



CSE Research Bulletin No. 14 January 2001Figure 1. Removal efficiency of E.Coli among

different control runs in MPCO reactorFigure 4. Comparisons of experimental data and

kinetic model.

Figure 2. Mineralization of E.Coli with respect toDO variations in MPCO reactor

Figure 5. SEM micrograph surface of E.Coli masscells prior to reactions.

Figure 3. Removal of E.Coli with respect to HRTs& DO variations in MPCO reactor

Figure 6. SEM micrograph surface of post- MPCOspecimen without any E.Coli mass cells subjected to

reactions at HRTs of 4.0 minutes.

y = -0.053xR

2 = 0.9856

y = -0.0368xR2 = 0.9661

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

00 10 20 30 40 50 60 70

HRTs(sec)

Ln(C

FUt/C

FUo)

DO=2.34mg/LDO=10.41mg/LDO=16.9mg/LDO=21.34mg/LDO=25.25mg/L

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15 20 25 30DO (mg/L)

(1-C

/Co)

Redu

ced

HRT = 15 secHRT = 30 secHRT = 45 secHRT = 60 sec


1

GEOTECHNICS

Analysis of Laterally Loaded Pile using Constrained OptimizationLow Bak Kong ([email protected])Teh Cee Ing ([email protected])

IntroductionWhen a horizontal force is applied to the top ofa pile embedded in soil, the resulting lateraldeflection is a function of the flexural rigidityof the pile and the soil pressure acting on thepile shaft. The soil pressure on the pile shaft inturn depends on pile deflection and soilproperties. This soil-pile interaction problem issimilar to that of a beam on nonlinear elasticfoundation. In the p-y curve method (Matlock,1970), the nonlinear pile-soil interface responseis modeled by a series of soil springs. Byproperly calibrating the p-y curves againstinstrumented interface response, the methodhas been shown to be capable of capturing thekey aspects of the laterally loaded pilebehaviour.

This article presents an alternative method ofperforming nonlinear p-y analysis of laterallyloaded piles, and demonstrates that the methodis easily extended to a stochastic nonlinear p-yanalysis in which the soil spring properties aremodeled as random fields. The robustness of

the proposed method is demonstrated in ananalysis involving p-y curves exhibiting strainsoftening.

Numerical procedure based on constrainedoptimizationThe pile is discretized into finite beamsegments. Strain compatibility andequilibrium among the segments and betweenthe segments and the soil springs areformulated as described in Low & Teh(1999), with modifications and simpleprogramming in the ubiquitous spreadsheetplatform to handle nonlinear p-y curves andnon-uniform discretization. The optimizationroutine that resides in most spreadsheetsoftware is used to obtain the pile deflectionprofile that satisfies force and momentequilibrium.

Analysis of offshore pile using strain-softening p-y curvesThis example is described in Tomlinson(1994, Example 8.2). A steel tubular pilehaving an outside diameter of 1.3 m and a

Deflection y (m)

0

5

10

15

20

25

-0.1 0.0 0.1Moment M (kNm)

0

5

10

15

20

25

-20000 0 20000

Soil reaction (kN/m)

0

5

10

15

20

25

-500 0 500

z = 0

Stiff claycu = 150 kPa

z = 23 m

water

y = 61 mm

y = 1 m

PH = 421 kN

steel pipe pile, d=1.3m

e = 26 Sea bed

Sea bed

Sea bed

Figure 1. Analysis of an offshore pile using the proposed method


2

wall thickness of 0.03 m forms part of a pilegroup in a breasting dolphin. The flexuralrigidity EpIp of the pile is 4,800,000 kNm2. Thepile protrudes 26 m above the sea bed and isembedded 23 m in the stiff over-consolidatedclay (cu = 150 kN/m2). The results of thespreadsheet optimization approach are shownin Figure 1, for the case where a cyclic force of421 kN is applied at 26 m above the seabed.The Matlock (1970) p-y curves for clays(Figure 2) have been used.

For the case in hand the p-y curves start from p= 0 at y = 0, and increases nonlinearly with thedeflection y to reach a maximum p value at y =0.0975 m. For y between 0.0975 m and 0.4875m, the p-y curve decreases towards a constantresidual value at y = 0.4875 m and beyond.Hence the p-y curve is nonlinear, exhibitsstrain-softening, and varies with depth. Thecalculated pile deflection at sea bed level(where z = 0) is 0.0605 m. The pile head is at e= 26 m above the sea bed. The deflection at pilehead is calculated to be 1.00 m, smaller thanTomlinson’s computed value of 1.36 m. Thedifference seems to be due to the simplifyingassumptions in Tomlinson’s analysis, whichrelied on charts based on elastic and uniformsoil modulus, and considered only the averageof the p-y curves in the top 2.5 m of soil belowsea bed. This resulted in conservative estimatesof the slope and deflection at sea bed level,hence overestimating the pile head deflectionby about 36%.

Separate analysis using a specially writtenFortran program to perform the finite elementanalysis with 60 equally spaced elementsyielded a pile deflection of 0.0596 m at seabed level, compared with 0.0605 m in Figure1, and practically identical shear and momentdistribution along the pile length. Thisverifies the accuracy of the constrainedoptimization approach for the case in hand.For the constrained optimization methodshown in Figure 1, it takes little effort to varythe pile embedment length for parametricstudies, and to test the robustness of theapproach when the strain softening part of thep-y curves are brought into play. The load-deflection curve for the case in Figure 1 butwith embedment length 10.5 m is shown inFigure 3, up to PH = 441 kN, for which thedeflection is y0 = 0.195 m at sea bed level,and 1.71 m at pile head. The curve indicatesthat the soil lateral resistance is nearly fullymobilized at PH = 441 kN, beyond whichphysical and hence numerical instability islikely to occur.

From deterministic to stochastic p-yanalysis

If the parameters (applied load and moment atpile head, and p-y curves) in the abovesection are average values, the computed pilehead deflection and maximum pile bending

-1500

-1000

-500

0

500

1000

1500

-0.3 -0.2 -0.1 0 0.1 0.2 0.3

y (m)

p (k

N/m

)

γ ' = 11.8 kN/m3

cu = 150 kN/m2

J = 0.25B = 1.3 mε = 0.01

z = 22 m

z = 0 m

z = 0 m

z = 22 m

12 m

z = 0

Stiff claycu = 150 kPa

z = 10.5 m

water

y = 131 mm

y = 1.366 m

PH = 421 kN

steel pipe pile,d=1.3 m

e =26 m

0

200

400

600

0 0.05 0.1 0.15 0.2Deflection at sea bed

(y0)

P H (a

t e =

26

m)

Figure 2. Matlock p-y model used inFigure 1

Figure 3. Load-deflection relationship.


3

moment represent, at best, only average values.

A more rational approach that takes intoaccount not just the mean values of theparameters but also their uncertainty is thereliability index approach, such as the invariantβ index defined by Hasofer and Lind (1974).The classical procedure based on transformedspace is available for reliability analysis.Alternatively, a practical and transparentprocedure was proposed in Low & Tang (1997)based on the perspective of

0

5

10

15

20

25

0 0.05 0.1 0.15 0.2

Pile top deflection (m)

Pro

babi

lity

dens

ity fu

nctio

n (P

DF)

PDF from Monte Carlo simulation

PDF from reliability index

an expanding ellipsoid that is tangent to thelimit state hypersurface in the original space ofthe random variables. This intuitive approachcan be used for stochastic nonlinear p-yanalysis of a laterally loaded pile. To illustrate,a reliability analysis for a pile of width 0.5 mand length 15 m has been carried out, assuminghyperbolic p-y curves. The random variablesare the correlated lateral load and moment atpile head, and the hyperbolic parameters at 21nodal points along the pile length. Thehyperbolic parameters at the 21 nodes arespatially autocorrelated based on the commonlyused negative exponential model of spatialcontinuity. Reliability indices corresponding todifferent values of limiting pile headdeflections were obtained automatically bycreating a short macro code in Microsoft Excelspreadsheet. The probability density functionplot (pink curve) shown in Figure 4 has beenobtained by applying cubic spline interpolationto the CDF curve, during which process the

derivatives (namely the PDF) emerged fromthe triadiagonal spline matrix. The wholeprocess is achieved conveniently usingstandard spreadsheet matrix functions. Anequally effective way of obtaining the PDF isto numerically differentiate the CDF curve.For comparison, a direct Monte Carlosimulation with 400,000 realizations wasperformed using a finite element programwritten for the soil structure interactionanalysis of laterally loaded pile. Thecomputation time is an order of magnitudehigher than that needed to obtain the βreliability indices. The PDF from the MonteCarlo simulations is plotted blue in Figure 4.

Probabilistic analysis of laterally loaded piles

Numerical modelling:l Nonlinear p-y curvesl Alternative solution: constrained

optimization approach.

Probabilistic analysis:l Hasofer-Lind indexl Stochastic soil mediuml Monte-Carlo simulation.

soil

pile

Load

soil

Summary and conclusions (Figure 5)

A numerical method based on constrainedoptimization in spreadsheet has beenpresented for the p-y analysis of laterallyloaded single piles. The same optimizationapproach also affords other possibilities, e.g.coupled analysis of nonlinear pile flexuralrigidity and p-y curves, optimization baseddesign, and reliability analysis. Such analysiswould be difficult or cumbersome bytraditional methods using specially writtenfinite element or finite difference programstogether with special-purpose reliabilityprograms.

References[1] Low, B.K., and Teh, C.I. (1999).

“Probabilistic analysis of pile deflectionunder lateral loads.” Proc., Int. Conf. ofApplications of Statistics and Probability

Figure 4. PDF from β indices and MonteCarlo simulation Figure 5. Features of the proposed method


4

(ICASP8), Melchers & Stewart (eds.), Sydney,Australia, Dec. 1999, Vol. 1, pp. 407-414.

[2] Low, B.K., and Tang, Wilson H. (1997).“Efficient reliability evaluation using

spreadsheet.” J. of Engrg. Mech., ASCE,New York, 123(7), 749-752.

[3] Tomlinson, M. J. (1994). Pile design andconstruction practice, 4th Ed., E & FN Spon,London.


Rainfall-Induced Slope Failures:Mechanism and Assessment

H. Rahardjo ([email protected])E. C. Leong ([email protected])R. B. Rezaur ([email protected])S. K. Tang ([email protected])C.N. Quan ([email protected])

Introduction

Two-thirds of Singapore’s land area is covered withresidual soils from the sedimentary Jurong and thegranitic Bukit Timah formations. Rainfall-induced slopefailures often occur in these residual soils as a result oftropical rainfall events. These slope failures can bedangerous, disruptive to development of infrastructureand costly to repair. An appropriate design philosophycan be adopted if the mechanism of rainfall-induced slopefailures is understood. The main objectives of this studywere to determine the mechanism that leads torainfall-induced slope failures in residual soil, to developguidelines for stability assessment against such failuresin Singapore and to evaluate several possible preventivemeasures.

Methodology

The methodology adopted for the research was asfollows [1]:

Four research slopes were selected (Figure 1). Two of theslopes were located in the residual soils of the graniticBukit Timah formation (Mandai and Yishun); and theother two slopes were located in the residual soils of thesedimentary Jurong formation (NTU-CSE andNTU-ANX).

Ground investigations were performed to establish thestratigraphy of the sites (Figure 2) and to collectundisturbed samples for laboratory testing. Laboratorytests were performed to characterize the residual soils ofthe research slopes by determining the index andengineering properties and the mineralogy of the soils.

The research slopes were fully instrumented to providereal time measurements of pore-water pressures andrainfall events on the slopes. An integrated solarpowered data acquisition system was developed tomonitor all readings of tensiometers, piezometers,temperature sensors and the rainfall gaugeautomatically (Figure 3).

The field monitoring results were analysed to determinethe magnitude and distribution of pore-water pressuresunder various climatic conditions (Figures 4 and 5), theinfluence of antecedent rainfall and the mechanism ofwater flow at the research slopes.

Slope stability analyses were conducted for the best andworst pore-water pressure distributions recorded in eachslope to determine the factor of safety for the slopes(Figure 6).

A parametric study was performed to model theinfiltration of rainfall into the residual soil slopes and itseffects on the stability of the slopes. Assessment chartsfor stability of slopes during rainfall were developed asshown in Figure 7.

Observations and analysis

From the field monitoring results on the four slopes, therainwater was observed to infiltrate the slope in thevertical direction and the highest infiltration appears tooccur near the crest. Initially, infiltration occursvertically downward towards the groundwater table.

Figure 1. Locations of the four selected research slopeswith reference to the major geological formation of

Singapore

Figure 2. Ground investigation for site stratigraphy inMandai slope

Figure 3. Data Acquisition System at Yishun slope


After a significant amount of infiltration, pore-waterpressures begin to build up and perched water tablesdevelop. Flow through a perched water table is mainly inthe downslope direction. The depth of infiltration appearsto be around 3 m. At the beginning of the rainfall event,the critical slip surface is deep seated. As rainwaterinfiltrates into the slope, the critical slip surface shiftsfrom a deep-seated slip to a shallow slip (i.e., 2 to 3 m).The influence of antecedent rainfall for a given slopeappears to be closely related to the permeability of thesoil in the slope.

Recovery of suctions between storms is due to verticalupward movement of water (evaporation) and utilizationof the soil water by the slope vegetation (transpiration)during dry days. The high infiltration of rain water intothe slope, however, does not lead to constantly wet soilconditions. This was observed in the rapid suctionrecovery during dry weather. The average suctionrecovery rates were 5 kPa per day for shallow depths and1 to 3 kPa per day for greater depths.

The parametric study revealed that slope angle andpore-water pressure distributions are important factorswhen assessing slope stability [1]. The height of the slopeis not a significant factor. Preventive measures andconstruction procedures can be undertaken to reduce therisk of rainfall-induced slope failures. One such methodis to use engineered soil covers to limit rainwaterinfiltration during wet periods while allowing forevaporation during dry periods.

Conclusions

The mechanism of rainfall-induced slope failures hasbeen studied extensively using four fully instrumentedslopes in the sedimentary Jurong and the granitic BukitTimah formations in Singapore. The result of the studyhas been disseminated in a monograph [2]. Initially,downward infiltration of rainwater can cause thedevelopment of a perched water table in the zone ofapproximately 3m below the slope surface. Subsequentwater flow through the perched water table is mainly inthe downslope direction. Design charts for preliminarystability assessment of typical slopes during rainfall havebeen made available in the monograph.

102 104 106 108 110 112 114 116 118 120 122 124

Distance (m)

Yishun Slope4 Dec 1998 @ 16:04

36

38

40

42

44

46

48

Elev

atio

n (m

)

Dry Period

(a) Contours of pore-water pressures in kPa

102 104 106 108 110 112 114 116 118 120 122 124

Distance (m)

36

38

40

42

44

46

48

Elev

atio

n (m

)


Dry Period

(b) Contours of total hydraulic head in meters

Figure 4. Measurements at Yishun slope during a dryperiod on 4-Dec-98 at about 4 pm

102 104 106 108 110 112 114 116 118 120 122 124

Distance (m)


36

38

40

42

44

46

48

Elev

atio

n (m

)

After Rainfall

(a) Contours of pore-water pressures in kPa

102 104 106 108 110 112 114 116 118 120 122 124

Distance (m)


36

38

40

42

44

46

48

Elev

atio

n (m

)

After Rainfall

(b) Contours of total hydraulic head in meters

Figure 5. Measurements at Yishun slope during a wetperiod on 6-Dec-98 at about 12 am


Engineered soil covers can be designed to limitinfiltration during wet periods while still allowing forevaporation during dry periods. Research in the area ofengineered soil covers or capillary barriers for slopestabilization is underway at NTU in order to developviable options for the local soils and climatic conditions inSingapore.

Infiltration at Crest for 20m Slope Standing at 27°

0.0

1.0

2.0

3.0

4.0

5.0

6.0

-80 -60 -40 -20 0 20 4 0 6 0 80

Pore-water pressure, u w , (kPa)

Dep

th (m

)

0 hrs 0.5 hrs 1.0 hrs 2.0 hrs 4.0 hrs Hydrostatic

Preliminary AssessmentChart for Slope

Stability

For:c′ = 10 kPaφ′ = 26°φb

= 26°H = 20 m

(a) -water pressure distributionsFactor of Safety for 20 m Slopes

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 1 0 20 30 40 50 60 7 0 8 0 90

Slope Angle (deg)

Fact

or o

f Saf

ety

0.0 hrs 0.5 hrs 1.0 hrs 2.0 hrs 4.0 hrs

(b) Respective factors of safety calculated using (a).

Figure 7. Preliminary stability assessment chart for 20 mslope during rainfall

Acknowledgment

The work was funded by a research grant from theNational Science and Technology Board, Singapore(Grant NSTB 17/6/16: Rainfall-induced slope failures).The authors gratefully acknowledge the assistance of Mr.JM Gasmo, Mr. MS Deutscher, Dr. David Toll and Mr.Ilias Tsaparas for the success of the project. Theassistance of the Geotechnics Laboratory staff of NTUand PWD staff in the field and laboratory work of thisstudy is gratefully acknowledged.

References

[1] Rahardjo H. 2000. Rainfall-induced slope failures.NSTB Report 17/6/16. School of Civil and StructuralEngineering. Nanyang Technological University,Singapore.

[2] Rahardjo H., Leong E.C., Deutscher M.S., GasmoJ.M., Tang S.K. 2000. Rainfall-Induced SlopeFailures. Geotechnical Engineering Monograph 3.NTU-PWD Geotechnical Research Centre, NanyangTechnological University, Singapore. 85 pp.

0

10

20

30

40

5012

-Oct

22-O

ct

01-N

ov

11-N

ov

21-N

ov

01-D

ec

11-D

ec

21-D

ec

31-D

ec

Date (1998)

Rai

nfal

l (m

m)

0

0.5

1

1.5

2

2.5

3

3.5

Fact

or o

f saf

ety

Rainfall (mm)

Factor of safety

Figure 6. Variation in factor of safety with time andrainfall for the Yishun slope


Undrained Cavity Expansion inModified Cam ClayL. F. Cao ([email protected])C. I. Teh ([email protected])M. F. Chang ([email protected])

IntroductionCavity expansion theory has been widely usedin the analysis of geotechnical problems.Published solutions differ mainly because ofdifferences in the constitutive models used todescribe the stress-strain behaviour of thematerial enclosing the cavity. Close-formsolutions, which are useful for theinterpretation of in-situ tests inoverconsolidated soil, are as yet not available.This investigation is concerned with theundrained cavity expansion in modified Camclay (MCC). A combination of large straintheory in the plastic zone and a small straintheory in the elastic zone was adopted inorder to simplify the solution. Anapproximate close-form solution wasdeveloped to facilitate the interpretation of in-situ tests.

Definition of the problemA cavity with an initial radius ao and an initialinternal pressure po in an unbounded three-dimensional medium of modified Cam clay isexpanded by a uniformly distributed internalpressure σa. When the cavity expands from ao

to a, an element initially located at a radialdistance ro from the centre of the cavity willmove to a new position at a radial distance rfrom the centre (Figure 1). The condition ofspherical symmetry holds in spherical cavity

r σθ

σr

a ao

ro

Plastic Zone

Elastic Zone

Figure 1. Expansion of a cavity

expansion, and the condition of axialsymmetry holds in cylindrical cavityexpansion. Plane strain condition is assumedfor the cylindrical cavity in the verticaldirection and the vertical stress σz is equal tothe mean of radial stress σr andcircumferential stress σθ in the undrainedcondition.

Elastic analysisThe solution for stresses and displacementcan be easily obtained based on theassumption of small strain. In the undrainedcondition, the volume change is zero. Themean effective stress is constant in the elasticzone. Consequently, no excess pore pressureis generated in the elastic zone.

Plastic analysisAfter the initial yielding at the cavity wall, azone of soil extending from the cavity wall toa radial distance rp will become plastic as thecavity pressure continues to increase. For asoil obeying the MCC model, the deviatorstress at the elastic-plastic boundary is 1−′= RpMq op (1)where R is the isotropic overconsolidationratio and M is the slope of the critical stateline in the p′:q plane. Combining the yieldingcondition and the elastic solution, the stressesand the displacement at the elastic-plasticboundary can be obtained.Once the soil has yielded, the total volumetricstrain will consist of the elastic and plasticvolumetric strains. In an undrained condition,the sum of the elastic and the plasticvolumetric strains should be zero in theplastic zone. This condition leads to arelationship between the mean effective stressand the deviator stress:

2

11

1

−

′′

′=Λ−

opp

RpMq (2)

where Λ is the plastic volumetric strain ratiodefined as (1 - κ/λ) and κ and λ are the slopesof the unloading-reloading line and thenormal compression line on the v:lnp' plane,respectively.


Adopting the logarithmic strains)/ln( or drdr=ε , )/ln( orr=θε , the

relationship between effective stresses andradial distance from the cavity centre can beexpressed as follows

21ln 1

11

+−=

−− +

++

mG

qr

aam

mo

m

−+

′

−Λ

− −− 1tantan32 11

1 RMpq

vMm

m

βκ (3)

where ( )( )( )( )

+−−′−−+′

=11/11/

ln21

1RMpqRMpqβ

and m is a constant. The shear modulus G canbe expressed as a function of the specificvolume v and effective Poisson’s ratio ν′. Figure 2 shows the deviator stresses arounda spherical cavity versus the radial distancefrom the cavity centre (normalized by cavityradius au) at the ultimate state (a/ao → ∞).When R < 2, the soil experiences plastichardening after yield and the deviator stressreaches the maximum value qu in the ultimatestate. When R = 2, the soil is perfectly plasticafter yield. The deviator stress in the plasticzone is constant and equal to qu. When R > 2,the soil undergoes plastic softening afteryield. The deviator stress increases to amaximum value qm and then decreases to qu asthe shear strain increases further. Except forheavily overconsolidated soils, differencebetween qm and qu is small.

Figure 2. Distributions of deviator stressaround a spherical cavity

An approximate close-form solutionIn practice, close-form expressions in terms oftotal stresses are more useful for theinterpretation of in-situ tests. Such a solutioncan be obtained by simplifying therelationship between the deviator stress andthe radial distance in the plastic zone.Assuming that q in the plastic zone is equal toqu (Figure 2), the cavity pressure and theexcess pore pressure at the ultimate state canbe approximately expressed as

++

+= Λ

Λ

)2/('2

ln12

'3 RMp

mGRMp

mp

oomouσ

(4)

−′+

+

=∆

Λ

Λ

Λ

21

)2/('

2ln

2'

3

Rp

RMp

mGRMp

mu o

ooma

(5)

ResultsThe stresses around the cavity are a functionof R, M, Λ, G and ν′. The most significantfactor which affects the magnitude of stressesis R. Figure 3 shows the pressure-expansioncurves for a cylindrical cavity with R from 1.1to 10. It clearly demonstrates that the cavitypressure changes very rapidly with thenormalized cavity radius if a/ao is less than 2.Beyond this value, the change in cavitypressure is insignificant.

Figure 3. Variation of normalized cavitypressure with cavity radius during the

expansion of a cylindrical cavity

0

1

2

3

4

5

1 10 100r/au

q/p'

o

R = 10

1.12

G/p'o = 100ν' = 0.3 M = 1.2 or φ 'tc = 30o

3

0

4

8

12

1 3 5 7 9 11a/ao

(a-

po)

/p'o

R = 10

3

1.1

G/p'o = 100M = 1.2ν' = 0.3


Figure 4 shows the changes in the excess porepressure at the cavity wall with R at theultimate state for the expansion of bothspherical and cylindrical cavities. Thenormalized excess pore pressure ∆ua/su

decreases as R increases (Figure 4(a)). Thiscorrelation opens up the possibility of usingpore pressure to estimate the in-situoverconsolidation ratio. The variation of∆u/p'o with R is dependent on the shearmodulus (Figure 4(b)). For G/p'o = 100, thevalue of ∆u/p'o increases as R increases. For asoil with a low G/p'o (say 20) and a highoverconsolidation ratio (R > 10), the oppositeis true. The results obtained from the approximatesolution were compared with the numericalsolution for the radial stress and the porepressure around a spherical cavity as shown inFigure 5. The differences between radialstresses obtained from the two solutions weresmall even though the approximate methodunderestimated the size of the plastic zone inslightly overconsolidated soils (R = 1.1).

Figure 4. Variation of normalized excess porepressure at cavity wall with R

ConclusionsA general procedure has been developed forthe analysis of the undrained expansion of acavity in modified Cam clay. The solutionswere formulated exactly and solved using asimple numerical integration. An approximateclose-form solution provides good estimatesof the radial stress and the circumferentialstress around the cavity and the pore pressurenear the cavity wall. The simplified solutionscould form a theoretical basis for theinterpretation of in-situ tests.

Figure 5. Comparison of stresses around aspherical cavity computed by the numerical

method and the approximate method

References[1] Cao L. F. (1997). Interpretation of in-

situ tests in clay with particularreference to reclaimed sites. Ph.D.thesis, Nanyang TechnologicalUniversity, Singapore.

0

1

2

3

4

(r -

po)

/p'o;

u/

p'o

Approx. close-form solution (AS)EP boundary for ASNumerical solution (NS)EP boundary for NS

R = 1.1G/p'o = 100M = 1.2

∆ u

σ r

-5

0

5

10

15

1 4 7 10r/au

(r -

po)

/p'o;

u/

p'o

R = 10

∆u

σ r

-2.5

0

2.5

5

7.5

10

ua/s

u

Spherical cavityCylindrical cavity

G/p'o= 100

(a)

20

-4

0

4

8

12

16

1 21 41R

ua/p

'o

G/p'o =100

20

(b)


[2] Cao, L.F., Teh, C.I. and Chang, M.F.(2000). Undrained cavity expansion inmodified Cam clay I: Theoreticalanalysis. Accepted by Géotechnique.

CSE Research Bulletin No. 14 January 2001Application of Cavity ExpansionTheory to the Interpretation ofPiezocone Test in Clay

M. F. Chang ([email protected])C. I. Teh ([email protected])L. F. Cao ([email protected])

IntroductionThe piezocone (CPTU) is a static conepenetrometer with the capability of measuring thepenetration pore water pressure in addition to thecone resistance and the shaft friction during aquasi-static penetration (Figure 1). Results ofCPTUs in clay are affected by the keyparameters such as the undrained shear strength,the overconsolidation ratio and the rigidity indexof the clay and they can be used for theevaluation of these parameters. In thisinvestigation, a theoretical solution of cavityexpansion in modified Cam clay was applied tothe interpretation of the piezocone test in naturalclays. Published piezocone data andcomprehensive test data in Singapore marine claywere used for checking the validity of theproposed interpretation methods.

Interpretation of cone tip resistanceBased on the solution of spherical cavityFigure 1. Piezocone test

expansion in modified Cam clay and taking strainrate effect into account, the cone resistance maybe expressed as

vorvot IOCR

Mq σσα ε ++

′=

Λ

)1(ln23

2 (1)

where αε is the strain rate factor, which can betaken as 1.64 for a 10 cm2 cone and 1.63 for a15 cm2 cone, σ′vo is the in-situ vertical effectivestress, Λ, the plastic volumetric strain ratio, canbe taken as 0.75, M is the slope of the criticalstate line, defined as 6sinφ′/(3-sinφ′), and φ′ isthe angle of internal friction.Equation (1) was found to provide a goodprediction of qt for most overconsolidated clays.Figure 2 shows the predicted qt profiles andCPTU results for a lightly overconsolidated clayin Bothkenna, Scotland. The predicted qt is ingood agreement with the measured values exceptfor a slight overprediction at the depth of 16 to18 metres.

Interpretation of penetration pore pressureBased on the spherical cavity expansion, the porepressure at the cone face can be expressed as

Λ

′+−=

2)67.01(

OCRMqu vott σα ε (2)

Figure 2. Predicted versus measured qt in alightly overconsolidated clay in Bothkennar

Figure 3. Predicted versus measured ut in a lightlyoverconsolidated clay in Ska-Edeby

0

4

8

12

16

20

24

0 500 1000 1500 2000

qt (kPa)

Dep

th (

m)

Predicted

Measured

φ' = 34o

Ip = 41OCR=1.4 - 3.5

CSE Research Bulletin No. 14 January 2001Figure 3 shows the predicted ut profiles for a

lightly overconsolidated clay in SkaEdeby,

Sweden. The predicted values are remarkablyclose to the measured values.Based on the cylindrical expansion analysis, thepore pressure at the cone base can be expressedas

vovotbtOCR

Mqu σσα ε 134.02

)66.01(23

+

′+−=

Λ (3)

Figure 4 Predicted versus measured ubt in alightly overconsolidated clay in Onsoy

Figure 4 shows the predicted and measured ubtprofiles for a lightly overconsolidated clay inOnsoy, Norway. The difference between the twoprofiles is negligible for lightly overconsolidatedclays

Estimation of OCR For piezocone with pore pressure measurementat the cone face, equation (2) can be rearrangedto express OCR as follows

( )

Λ

ε σα

/1

' 67.012

+−

=M

uqOCR

vo

tt (4)

For piezocone with pore pressure measurementat the cone base, OCR may be obtained basedon equation (3) as follows

( )

Λ

ε σασ

/1

' 66.01134.0866.0

2

+

−+=

Muq

OCRvo

btvot (5)

Figure 5 shows the predicted OCR profile for thelightly overconsolidated clay at a site inEmmerstad based on the measured qt and ubt.The predicated profile agrees well with theoedometer data.

Estimation of undrained shear strength

Form MCC, ( )Λ′= 2/5.0 OCRs ou σ . Once theOCR is obtained, su may be estimated. Equations(4) and (5) can be arranged to give

Figure 5 Predicted OCR profile using qt and ubt

for a low plasticity clay in Emmerstad

)'sin1(

'sinφα

φ

ε += e

uq

s (6)

where qe is the “effective” cone resistancedefined as )134.0866.0( btvot uq −+ σ or

)( tt uq − .

0

4

8

12

16

0 200 400 600ut (kPa)

Dep

th (m

)

PredictedMeasured

φ' = 30o

Ip = 30 - 55OCR = 1.1 - 2.6

0

4

8

12

16

20

24

0 200 400 600 800

ubt (kPa)

Dep

th (m

)

Predicted

Measured

φ ' = 34o

Ip = 30OCR = 1.1 - 1.6

0

2

4

6

8

10

1 2 3 4 5

OCR

Dep

th (m

)

OedometerPredicted

φ ' = 39.3o

Ip = 8 - 14


Estimation of rigidity indexFrom equations (1) to (3), Ir can be expressed asa function of qt and ut or ubt as follows

1'sin

)'sin1(43

)ln( −

−+=

e

votr q

qI

σφ

φ (7)

Application to Singapore marine clayA very detailed and extensive soil investigationprogramme was implemented at a major landreclamation project at Changi East in Singapore.Figure 6 shows typical profiles of OCR, su and Ir

predicted using the methods proposed. The OCRvalues predicted from the piezocone test datagenerally agree with those obtained fromoedometer tests, except at depths of 21 to 24metres. The predicted su agrees with su from thefield vane test (FVT). The predicted su alsocompares favourably with the results of triaxialundrained compression tests on Ko-consolidated samples (CKoU). The rigidity indexIr predicted from the CPTU data is in broadagreement with those obtained from four CKoUtests and one CIU test (triaxial undrainedcompression test on isotropically consolidated

sample) for which the secant Young’s modulus atone-half the failure stress is used in deriving Ir.

ConclusionsThe theoretical solution for the expansion of acavity, both cylindrical and spherical, inModified Cam clay was applied to theinterpretation of the piezocone test in clay. BothOCR and su can be estimated from the correctedcone resistance and the penetration porepressure without the need of assuming Ir. Therigidity index Ir can also be estimated from themeasured quantities in the CPTU.The proposed framework has been applied to anextensive database of CPTU data in a widevariety of clay deposits from different parts of theworld. The comparative study of the predictedparameters and the results obtained by otherindependent means has affirmed the generalvalidity of the proposed approach.

References[1] Cao L. F. (1997). Interpretation of in-

situ tests in clay with particular referenceto reclaimed sites. Ph.D. thesis, NanyangTechnological University, Singapore.

[2] Chang, M.F., Teh, C.I. and Cao L. F.(2000). Undrained cavity expansion in

modified Cam clay II: Application to theinterpretation of piezocone test.Accepted by Géotechnique.

Figure 6. Soil parameters deduced from piezocone tests in Singapore marine clay

0

5

10

15

20

25

30

35

Soil stratification

Dep

th (m

)

Upper marine clay

Silty clay

Lower marine clay

Sandy clay

1 3 5

OCR

PredictedOedometer

0 50 100su (kPa)

PredictedField vaneTriaxial CKoU

0 100 200Ir

PredictedTriaxial CKoUTriaxial CIU


A Variational Solution for Laterally Loaded Single Piles

W Y Shen ([email protected]) C I Teh ([email protected])

IntroductionA number of theoretical methods have been developed for the analysis of laterally loaded singlepiles, for example, the closed form solutions (Hetenyi, 1946) for a soil modelled using the subgradereaction method, and the boundary element analysis (Poulos, 1971) for a soil modelled as an elasticcontinuum. This paper examines a variational method for the analysis of laterally loaded singlepiles in a soil modelled either using the subgrade reaction method or an elastic half space. The mainfeature of the present method is that the displacement of the pile is represented by a finite series.The principle of minimum potential energy is used to determine the response of the pile. Thepresent solutions compare well with those obtained by other methods and field measurements.

Method of analysis(a) Basic variational formulationThe potential energy of a pile subject to a horizontal load H and moment M at the pile head can bedescribed in the form

Mz

uHuddzpudz

zu

IE tt

lz

Tz

l

zppp ∂

∂−−+

∂∂

= ∫∫ 21

2

2

2

21π (1)

The first term is the elastic strain energy of the pile, where pE is the pile Young’s modulus, pI isthe second moment of area of the pile section, z is the depth co-ordinate, and zu is the horizontaldisplacement of the pile. The second term is the work done by soil reaction pressure zp along thepile shaft. The third and fourth terms are the work done by the external horizontal load H andmoment M acting at the pile head, respectively, where tu is the horizontal displacement of the pileat the pile head. For soil modelled using the subgrade reaction model, zp in equation (1) can bereplaced by zhz ukp = (2)where hk = the soil subgrade reaction coefficient, and this quantity can vary with the depth in anarbitrary manner to reflect the soil profile. The horizontal displacement of the pile can be assumedto be given by a function in the form { } { }aZu T

z = (3)where { }TZ is a vector related only to the co-ordinate z , and the vector { }a is a set of undeterminedcoefficients. The principle of minimum potential energy then requires that pπ be an extremumwith respect to the admissible displacement field characterised by the vector { }a . Hence

0=∂δ

∂π p (4)

where δ denotes the individual coefficients used in the vector { }a in equation (3). Thus, thepotential energy in equation (1) reduces to the following expression

MHu

dzuKu

dzzu

IE zu

t

lzs

Tz

l

zu

zpp

tz

δδδδ ∂

∂+

∂∂

=∂∂

+∂

∂

∂∂ ∂

∂∂

∂

∫∫)()( 2

2

2

2

(5)

The above equation can finally be rewritten in a matrix form as [ ] [ ]( ){ } { }tsp Pakk =+ (6)

in which [ ]pk and [ ]sk are matrices related to the pile stiffness and soil stiffness, respectively, and{ }tP is a vector related to the load at the pile head. The vector of unknown coefficients { }a can nowbe solved under the known external loads H and M at the pile head. The horizontal displacement,rotation and bending moment along the pile shaft can then be obtained analytically based on theassumed function in equation (3).

The above variational solution procedures are applicable to the analysis of a single pile when thesoil is modelled using an elastic half-space instead of the subgrade reaction model described above.The only difference is in the second term [ ]sk in equation (6). [ ]sk is evaluated based on Mindlin’spoint load solution when the soil is modelled as an elastic half space.

(b) Horizontal displacement function for pileTwo finite series are constructed such that the deformation and force boundary conditions of a pileat both the pile head and the pile toe can be closely satisfied. The two series model the lateraldisplacements of single piles subjected to a horizontal load only and a moment only, respectively.The horizontal displacement of a pile subject to a horizontal load H at the pile head is assumed tobe given by

l

zmlz

bauk

mHmHHz

πα∑=

++=3,2,1

sin (7)

in which Ha , Hb and Hmα are the unknown coefficients, and k is the number of terms used in thetrigonometric function. The horizontal displacement function of a pile under a moment loading atthe pile head is approximated by

lzn

lz

bauk

nMnMMz 2

cos12

5,3,1

πα∑−

=

++= (8)

in which Ma , Mb and Mna are the unknown coefficients, and k is the number of terms used. Otherloading conditions can be easily treated as the superposition of the above two loading conditions. Afixed-head pile can also be solved in a conventional way based on the solutions for free-head pilesby imposing the zero-rotation condition at the pile head.

Result of analysisComparisons between the present method and existing methods and field measurements werecarried out to validate the accuracy of the present solutions. It was found that 20 terms (i.e. 20=k )in the trigonometric function of the assumed finite series is quite sufficient to represent the responseeven for extremely flexible piles with 610 −=rK .

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+01E+0

1E+1

1E+2

1E+3

1E+4

1E+5

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+01E+0

1E+1

1E+2

1E+3

1E+4

1E+5

Poulos (1980)

Present method

Verruijt and Kooijman (1989)

FI ρ

HIρ

HM II θρ ,

MIθ

(a) Soil modelled using subgrade reaction method (b) Soil modelled as an elastic half-space

I

rK

MIθ

HIρ

FI ρ

HIθI

RK

Hetenyi’s method (1946)

Present method

25=dl

lz

lz

Comparisons with the closed-form solutions by Hetenyi (1946) and the boundary element solutionsby Poulos (1980) as well as the finite element analysis by Verruijt and Kooijman (1989) are shownin Figure 1, where HI ρ , MI ρ , HIθ , MIθ and FI ρ are a set of deflection and rotation factors at thepile head. Good agreement between these solutions can be observed. The deflections and rotationsfactors obtained by Poulos (1980) were underestimated for very flexible piles due to the limitednumber of soil elements used in his solutions. Results of other comparisons all show very goodagreement.

Lateral pile loading tests by McClelland and Focht (1956) were analysed using the variationalapproach. The single pile tested had a diameter of 0.61 m with a bending rigidity 465 2MNm andwas embedded into normally consolidated clay to a depth of 23 m . The shear strength of the clayincreased linearly with depth. In the analysis, the two soil models, i.e. the subgrade reaction modeland elastic half-space were both used to model the soil and the soil parameters were back-analysedbased on field measurement of pile deflection at the pile head. The modulus of subgrade reactionand the Young’s modulus of the elastic half-space backfigured were 36.3 mMNdzk h = and

23.4 mMNzEs = , respectively, where z is the depth co-ordinate and d is the pile diameter. Acomparison of the profiles of bending moment and deflection along the pile shaft under a workingload are shown in Figure 2. The computed results from the two soil models are both in goodagreement with the field measurements. It seems that both models are able to predict the deflectionand bending moment profiles of a laterally loaded pile reasonably well.

ConclusionsA variational approach that can be used to analyse laterally loaded single piles in a soil modelledusing the subgrade reaction model and an elastic half space has been developed. The paper hasdemonstrated that the displacements of single piles can be represented accurately by the finiteseries presented in the paper. The variational solutions based on the subgrade reaction model andelastic half-space have been shown to be able to predict the deflection and bending momentdistributions of laterally loaded single piles.

Figure 2. Comparison of deflection and bending moment distribution

(a) Deflection (mm)

-20 0 20 40

0.0

0.2

0.4

0.6

0.8

1.0

Subgr ade re actionsolutionElastic half-spacesolutionTe st of Mc Clellanda nd Focht (1956)

-0.4 0.0 0.4 0.8

0.0

0.2

0.4

0.6

0.8

1.0

Subgra de r eac tionsolutionElastic half- spa cesolutionTest of M cClellandand Focht ( 1956)

(b) Bending moment (MN.m)

Figure 1. Deflection and slope factors

With the use of the variational method, the displacement of a pile along the pile shaft was simulatedby a finite series. Therefore, no discretisation of the pile as required in the finite difference orboundary element method was necessary, and the displacement and bending moment distributionalong the pile can be obtained analytically. Analytical solutions can be achieved for both constantsoil stiffness and soil stiffness varying with depth when the soil is modelled using the subgradereaction method. Hence, the present method is to some extent more efficient than other existingmethods such as the boundary element method. The variational approach is by no means limited tosingle piles. It can be extended to the analysis of laterally loaded pile group.


STRUCTURES

Behaviour of an Interlocking Steel BeamT K Chan ([email protected])

Introduction

A new interlocking steel section, which isfabricated from a pair of straight webinterlocking steel sheet piles acting as theflanges, and two welded steel plates as thewebs, to form a box section of 500x300mm isintroduced (Figure 1).

Figure 1. An interlocking steel section

A number of these sections can be interlockedto form a beam, roof or wall to carry lateralloads (Figure 2). This new steel section isbeing evaluated as an alternative to the piperoof system of supporting trenchless culvertor tunnel excavations and is expected toprovide economical, safe and quickconstruction. Existing pipe roof supportsystem requires the use of microtunneling toinstall interlocking steel pipes to form atemporary support structure inside which apermanent structure may be built. Thismethod is especially useful in heavily built-upareas and for the construction of underpassesacross busy roads. It is obvious that this dualsystem of a temporary and permanent systemis redundant and can be improved upon bycombining the two systems into one. Thisproject investigates the behaviour of a 3.0mbeam, which consists of six interlockingsections. The beam was 1.0m wide, 300mmhigh and loaded in four-point bending toinvestigate the ultimate capacity and the load-deformation characteristics.

Figure 2. Prototype beam specimen

The performance of the interlock waspreviously confirmed by tensile testing tofailure and was found to exceed theguaranteed minimum pull-out strength of5000kN/m. The interlock was very effectivein load transfer as the material in the webcould be stressed to more than 90% of theultimate strength.

Interlocking beam specimen

The new interlocking steel section, which isfabricated from a pair of AS500-12.7 straightweb interlocking steel sheet piles acting as theflanges, and two 13mm thick welded steelplates as the webs, to form a box section of500x300mm (Figure 1). The vertical webswere welded with full penetration fillet weldsto the sheet piles to provide full momentcapacity. The depth of the section was300mm and, for ease of handling, thesegments were limited to 1000mm length.The mechanical properties of the sheet pilesand web plates are summarised in Table 1.

Table 1. Mechanical properties of sheet pileand web plate material

Material fy(MPa)

fult

(MPa)E

(GPa)Sheet Pile 491 584 205Web Plate 463 563 212

Six interlocking sections were connectedtogether as shown in Figure 2. They weresimply supported on two concrete pedestalsand load tested under four-point bending.Each section of 500x300x1000mm was

AS500sheet pile

a=300webplate

2502b=500

3000 = 6@500

300

PP


interlocked with the adjacent section at twocorners. The selection of the sections was on acompletely random basis. All the sectionswere able to fit and interlock properly as thesesections were fabricated to very tighttolerances. The beam specimen exhibited aninitial deflection of 30 mm due to slack in theinterlocks of the steel section.

The load was applied using a 2000kNhydraulic jack and distributed to the two loadpoints with a spreader beam. The appliedload, deflections at 14 locations and strainreadings from 51 gauges were recordedautomatically on a data logger connected to acomputer during the test. The readings wererecorded at 10kN load intervals, but when thespecimen exhibited nonlinear behaviour thereadings were taken at regular displacementintervals until failure.

The force in the top and bottom sheet pilescan be computed from the data measured bythe strain gauges. The top sheet pile was incompression and the bottom sheet pile intension; this is consistent with a beam underapplied positive bending moments.

The initial load-deflection behaviour waslinear with a sudden jump in the verticaldeflection at 20kN, possibly due to a slip inthe interlocks. It continued to increase linearlyuntil the load exceeded 50kN upon which thebeam exhibited a nonlinear load deformationresponse.

The specimen failed with a crack at the weldconnection between the straight web sheetpile (member AB) and the web plate of thefirst steel section (member AC) where theshear force across the section is largest. Thisoccurred at a total load (2P) of 501kN with acorresponding vertical deflection of 152mm.This may be due to a lack of weld penetrationat the web plate.

Moments, forces and deflections

A model of the structural behaviour can beobtained by assuming that the interlocks arepins or hinges, and can only transmit axialand shear forces. The internal forces anddisplacements were calculated by adoptingthe slope-deflection method where it wasassumed that axial deformation of memberswas negligible.

73P

Bending Moments

P

A

B

C E G I

D F H J

63P

63P

63P

52P

K

L

LC

P

63P

52P

73P

52P

115P

73P

52P

73P

115P

73P

Figure 3. Bending moment diagram for the beam specimen (left-half shown, units BM is Nmm)


The bending moment diagram is shown inFigure 3. As expected, the largest bendingmoments and shear forces occur at themembers in the shear zone. The web platescarry the larger moments and forces due to itsgreater length compared to the sheet piles.Members in the constant bending zones aresubjected to very small moments and shearforces. However, the axial forces in the sheetpiles are highest in the constant bendingmoment zone with tension in the bottommembers and compression in the top. Theweb plates at the supports and load pointscarry half the reaction and point load,respectively, indicating that the load isequally distributed to the top and bottom sheetpiles.

The deflection at mid-point of the beamspecimen is

)13(2

3126

8

2

2

2

+++=∆

αααα

K

Pb (1)

where P is the applied point load, K1 equals toIw/a, K2 equals to Isp/b, and α is the ratioK1/K2. Iw and Isp are the sectional moduli ofthe web and sheet pile, respectively.

The deflections obtained from the test and theanalysis are plotted together in Figure 4. Thetest results and the prediction are very closeunder low loads but started to deviate whenthe load exceeded 300kN. This deviation isdue to the non-linear behaviour of theinterlock where the interlocking finger andthumb starts to deform and affects thestructural performance of beam specimen.

Conclusions

A new structural system for culvertconstruction is presented and discussed. Theresult of a preliminary investigation on thestructural behaviour of a prototype beam hasindicated that the forces and elasticdisplacements can be predicted by usingconventional methods of analysis. However,the displacements at higher loads, where thenon-linear effects of the interlock becomemore significant, may require a more complexanalysis. Future work will concentrate ondeveloping models to predict the non-linearbehaviour of these specimens.

Figure 4. Displacement of Points E, G, I andK

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80 90 100

Displacement (mm)

Loa

d, P

(kN

)

Pt.E

Pt.G

Pt.I

Pt.K

Analysis


Analysis of Tubular T-Joint Under Combined Axial and BendingLoading

S T Lie ([email protected])S P Chiew ([email protected])S Sun ([email protected])

Introduction

Tubular joints have been extensively used in the offshore industry for many years as they

combine strength with minimum resistance to wave forces. In order to study the behaviour of

such structures, a special purpose test-rig is constructed in the Heavy Structures Laboratory for

conducting the static and dynamic tests of tubular welded T, Y or K-joints. The static test

results are reported herein. Both the strain gauges specimen testing which includes the basic

brace axial, in-plane-bending (IPB), out-of-plane-bending (OPB) and combined loading cases,

and also the finite element analyses were carried out in this study. The maximum stress

locations, or frequently referred to as the hot spot stress (HSS) locations, are important

information for deciding on the placement of the probes in the fatigue tests using the

Alternating Current Potential Drop (ACPD) technique.

Stress concentration factors

A tubular T-joint can be subjected to three types of basic load, i.e. axial loading, in-plane-

bending moment (IPB) and out-of-plane bending moment (OPB), at the brace end as shown in

Figure 1. Each of the load type will cause a different stress distribution on the joint. Stress

concentration factors (SCFs) caused by the above three basic load cases have been studied

extensively by many researchers. However, very few combined loading results have been

reported in the literature.

Some researchers have studied the member and load interaction effects on tubular joints, and

they have proposed a parametric equation of the form:

opbBoipbBiaxA )()()()( fKfKfK φ+φ+φ=φσ [1]

where )(φσ is the hot spot stress, )(A φK , )(Bi φK and )(Bo φK specify the stress concentration

factors about the chord/brace intersection of a joint subjected to unit axial load, IPB and OPB

respectively, and axf , ipbf and opbf are the corresponding nominal stresses. These researchers

have also proposed a procedure for predicting the combined HSS based on the linear


superposition of stresses of individual joint members, and used a combination of parametric

equations and influence factors. In the present study, the results by superposition method are

compared with those results obtained directly from the experimental tests.

Figure 1. Brace end connected to the three actuators

Experimental testing

One 25 ton and two 10 ton capacity hydraulic servopulser actuators as shown in Figure 1, were

used to produce the three basic load cases using the Labtronic 8800 Instron controller. The

loads were applied along the three mutually perpendicular axes. The actuators can be operated

individually or simultaneously to produce the combined loading. The 25 ton actuator was used

to apply the axial loading, while the 10 ton actuators were used to apply the IPB and OPB

loading. The chord ends of the specimen were mounted on to the test-rig using eight bolts per

chord end, creating a fixed-end condition for the chord. The weld design and preparation were

in accordance with American Welding Standards.

The strain gauges were placed around the entire chord/brace intersection on both brace and

chord at 150 interval, with additional strain gauges being added to counter-check the measured

results. Gauges were placed on the outside surface of both brace and chord. A general view at

the intersection region is illustrated in Figure 2. The strain gauges measured the strain caused

by membrane and bending effects on the outer surface where the peak hot spot stresses were

expected. Four single-element strain gauges were attached at 900 intervals around the brace,

midway between the chord/brace intersection and at the loading point, to measure the nominal

load. All the strain gauges were connected to TML ASW-50A switch boxes which in turn were

connected to a TML TDS-801 data logger. Strain output was recorded on a paper tape. All the


principal stresses were calculated from the extrapolated directional strains at the weld toe

location.

The specimen was first subjected to an incremental static load on each axis separately, then

combined load was applied. The axial load range was from kN 50 to kN 100 . For IPB, the

minimum and maximum load applied were kN 5 and kN 10 respectively, while for OPB, the

load was increased from kN 3 to kN 9 . Maximum variation of load was recorded to be

kN 0.1± .

Figure 2. Close-up view at the intersection region of the specimen

Experimental and numerical results

Figure 3 shows the hot spot stress distribution around the intersection under combined loading,

a fixed IPB of kN 10 and increasing OPB for Load Case (LC) 6.7 to 6.9 from kN 3 to kN 9 . It

indicates that the stress distribution is not symmetrical, and the hot spot stress location is not

always located at the saddle or at the crown. For LC 6.7 to 6.9, the peak hot spot stress location

has shifted from 1500 to the lower saddle. Figure 4 shows the hot spot stress distribution around

the intersection under combined load for LC 5.2 when the axial load is kN 50 and OPB is

kN 6 . The results obtained by direct experimental analysis were compared with the results

obtained by superposition method. It shows that the direct analysis results were generally lower

than the superposition method results. But at the hot spot stress location, i.e. at the lower

saddle, the region near the hot spot stress location, the trend was reverse and direct analysis

results were higher than the superposition method results.

The results obtained by the Marc/Mentat finite element analyses prove the accuracy and

reliability of the experimental results. Figure 5 compares the experimental hot spot stress


distribution around the intersection with the finite element results under combined load for LC

6.7 with IPB of kN 10 and OPB of kN 3 . It is found that the numerical results generally agree

well with the experimental results. Hence, the numerical results confirm that the experimental

results are reliable.

Figure 3. Stress distribution along the chord/brace intersection for fixed IPB and varying OPB

Figure 4. Comparison of hot spot stress distribution along the chord/brace using superposition

and direct analysis methods

ANGLE FROM SADDLE (DEGREES)

0 100 200 300

HO

T S

PO

T S

TR

ES

S O

N B

RA

CE

(M

Pa

)

-80

-60

-40

-20

0

20

40

60

80

100LC 6.7LC 6.8LC 6.9


0 100 200 300

HO

T S

PO

T S

TR

ES

S O

N B

RA

CE

(M

Pa

) (L

C 5

.2)

-40

-20

0

20

40

60DIRECT ANALYSIS

SUPERPOSITION


Figure 5. Comparison between experimental and numerical stress distribution along thechord/brace intersection for combined IPB and OPB

Conclusion

The study shows that the peak hot spot stress locations of the T-tubular joint when subjected to

combined loading, shift from those of the basic load cases. Generally, the peak hot spot stresses

obtained by superposition are higher than that by direct analysis except for the areas that are

near to the peak hot spot stress locations.


0 100 200 300

HO

T S

PO

T S

TR

ES

S O

N B

RA

CE

(M

Pa

) (L

C 6

.7)

-60

-40

-20

0

20

40

60EXPFEM


Nonlinear Dynamic Response Analysis and Damage Assessment of RC Structuresto Blasting Ground Motion

H Hao ([email protected])Y Lu ([email protected])G W Ma ([email protected])

Summary

High-frequency ground motions generated byunderground explosions may cause damage tosurface structures. Traditional seismicanalysis of structures normally discretizes aframe structure with beam-column elements.However, beam-column element may not besuitable for estimating material damage andstructural damage produced by high-frequency ground motions. In the presentproject, reinforced concrete plane frames arediscretized by plane stress elements filledwith concrete material and smearedreinforcement. A fracture indicator varyingfrom 0 to 1 is defined to measure the crackingstatus of concrete from micro- to macro-level.The development of plastic hinge controlledby reinforcement yielding is, however,monitored by a plastic indicator. The globaldamage index of the entire structure isdetermined by structural stiffness degradationwith reduction of natural frequency. Shakingtable test results of a 1:5 scale single-storeymodel are employed to calibrate the numericalsimulation. A two-storey, a six-storey and aten-storey frames were subsequently analyzedby the validated model. It was found that thehigh-frequency ground motion led to differentdamage characteristics from seismic motionin both material and structural level. Theregulations for inhabited building distance forunderground ammunition storage design arevery conservative for modern reinforcedconcrete structures.

Methodology

The present study uses a damage model withdouble scalars, tD and cD , defined as

++++ −−−= 00 /)(1 εεεαeDt and−−−− −−−= 00 /)(1 εεεαeDc (1)

in which +α and −α are damage parameters;+0ε and −

0ε are respectively the threshold

strains in the uniaxial tensile and compressivestates. +ε and −ε are equivalent tensile andcompressive strains of concrete, and they are

∑=

++ =3,1

2)(i

iεε and ∑=

−− =3,1

2)(i

iεε (2)

where +iε is positive principal strain, the

superscript (+) means it vanishes if it isnegative. −

iε is negative principal strain and it

vanishes if it is positive.

Fracturing in the concrete is characterized bydefining a fracture indictor. The reinforcedconcrete component is considered to beremaining in elastic state if the equivalenttensile strain +ε is less than the thresholdtensile strain +

0ε of concrete. When +εexceeds +

0ε but is less than the steel yield

strain s0ε , the reinforced concrete is in the

stage of micro-crack. Large cracks occurwhen the equivalent tensile strain exceeds theyield strain of reinforcement. Forreinforcement, a plastic indicator is used toidentify the plastic flow. It is determined bythe effective plastic strain and variesirreversibly from 0 to 1 with the thresholdplastic strain and the ultimate strain. Themaximum value 1 of the plastic indicatorimplies complete failure of the local areawhere a plastic hinge is formed.

Global damage of a structure can becharacterized by its stiffness degradation. Itcan be represented by the reduction of itsnatural frequency as

20

2

1f

fD c

g −= (3)


where 0f and cf are, respectively, the initial

natural frequency and the current naturalfrequency of the structure.

Calibration with data from scaled modeltest

The shaker used in the experiment has a 1×1m2 sliding table and can achieve themaximum acceleration of 120g and themaximum frequency of 3000 Hz. Only thehorizontal excitation was considered in thecurrent tests, due to the limitation of the testequipment. The scaled model, whichmeasured cracks and the numericallysimulated fracture indicator are illustrated inFigure 1. It was found that not only thedamage contour, but also the response timehistories at the measurement points as shownin Figure 2 are in very good agreementbetween the numerically simulated and themeasured results.

Applications

A two-storey, a six-storey and a ten-storeyframe were subsequently analyzed based onthe validated model. Ground motions to excitethe structure were generated by numericalsimulation of a 250 ton undergroundexplosion. The numerically simulateddamages of the three structures to the groundmotions at a surface distance of 50 m areillustrated in Figure 3. It was found that the

major concrete damage was generallydistributed and limited at the low storeys. Thedamage profiles are quite different from thoseresulting from a seismic motion in which thedamages are always concentrated at the beam-column joints.

Responses of structures with infilled masonrywere also examined. Figure 4 gives theconcrete damage and masonry damageseparately. It can be seen that the damageprofiles of the frames are quite different fromthose of the bare frame. Only the first infilledframe with masonry infilled in the lowerstorey experienced major concrete damage onthe first storey columns. Damage to beams forall the infilled frames was reduced. Themasonry damage, on the other hand,depended significantly on infilling pattern ofmasonry. Major masonry damage alwaysoccurs near the interface with RC frame andat the opening corners.

The global damages of the three frameslocated at different surface distances tounderground explosion-induced groundmotions are plotted in Figure 5. Differentzones, i.e. major, moderate, and minordamage, are defined based on the globaldamage indices. They can be used todetermine the safe inhabited buildingdistances around an underground blasting site.


Figure 1. Calibration using shaking table test results

Time (Second)

Base motion

0 0.1 0.2 0.3 0.4 0.5-90

-60

-30

0

30

60

90

ExperimentalNumerical

Time (Second)

Response at mid height of column

0 0.1 0.2 0.3 0.4 0.5-120

-80

-40

0

40

80

120ExperimentalNumerical

Time (Second)

Response at floor level

0 0.1 0.2 0.3 0.4 0.5-12

-8

-4

0

4

8

12

ExperimentalNumerical

Figure 2. Comparison of response acceleration time histories (m/s2)

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5

Character distance (Q1/3)

Glo

bal d

amag

e

Ten-storey frame

Six-storey frame

Two-storey frame

Minor

Moderate

Major

(a) Concrete damage

(b) Masonry damage

Figure 4. Effect of infilled masonry

Figure 5. Global damage indices

(a) (b) (c)

Figure 3. Damage of different structures


1

Behaviour of Full-Scale Lightly Reinforced Concrete Beam-Column Joints

Yin Hui ([email protected])Paulus Irawan ([email protected])

Introduction

Beam-column joints are one of the mostcritical parts of a frame structure underseismic loading. However, reinforcedconcrete beam-column joints in the non-seismic region are normally designed to resistgravity load only, so they possess structuraldetails that are in contrast to the modernseismic design. This project investigated thebehaviour of this class of lightly reinforcedconcrete beam-column joints under simulatedearthquake excitation – reversed cyclicloading. The experimental study presentedhere included a testing on four full-scalelightly reinforced interior beam-column jointstypical of a low-rise industrial building inSingapore. The effect of column axial load(15% column squash capacity) and bonddeterioration along main bars passing throughthe joint panel is highlighted.

Experimental testing

The dimensions and reinforcement details foreach specimen are shown in Figures 1 (a) and(b). The typical details of these lightlyreinforced concrete interior beam-columnjoints are as follows:

1. No horizontal or vertical links wereprovided within the joint region.

2. Around 2% longitudinal columnreinforcement was provided with lapsplices all locating immediately abovefloor levels in the zone of maximumlateral load and moment. Widely spacedcolumn links were present.

3. Within the joint region, the area of the topbeam reinforcement was twice as large asthat of the bottom.

4. Bottom beam bars in the vicinity of thejoint region were either discontinuous orwith very short embedment length into thejoint core.

The properties of the specimens and theprediction of the induced joint shear stress areshown in Table 1. The reversed cyclic loadingas shown in Figure 2 was applied at the endsof the beams to produce cantilever bending ofthe beams and asymmetrical double curvaturein the columns.

Figure 1(b) Elevation view of specimen C4

Figure 1(a) Elevation view of specimen C1

Table 1 Specimen propertiesParameters Specimen Type

Units C1 C4Beam length L mm 5400 5400Section width bb mm 300 300

Section height hb mm 550 550

Top reinforcement 5Y32 6Y32Beam Bot. Reinforcement 2Y32 3Y32

Anchorage hc /db ratio 13.1 10.0Top yielding moment Myb kN.m 785 927

Top ultimate moment Mub kN.m 840 1003

Bot. yielding moment Myb kN.m 378 553

Bot. ultimate moment Mub kN.m 395 576

Joint shear stress based on Myb N/mm2 14.9 22.4Column height H mm 2895 2895Section width bc mm 350 400Section height hc mm 500 400

Column Reinforcement 8Y25 8Y25

Anchorage hb /dc ratio 20 20Compressive axial load Ton 65/Nil 60/NilUnconfined yield moment Myc kN.m 292 244Joint shear stress based on Myc N/mm2 9.24 7.72


2

Based on ACI 318-99 design code, for ductilebeam-column joints, the joint shear resistingcapacity contributed by the concrete coreitself was predicted to be 2 N/mm2 forspecimens with column axial load (C1A andC4A) and 1.5 N/mm2 for specimens withoutcolumn axial load (C1B and C4B). Since thejoint shear needed to induce beam and columnhinging is much larger than the joint shearresisting capacity in the joint, it is obviousthat the joint core is likely to be the weakestpart compared to the beams and columns.

All four specimens experienced joint panelfailure with large block of concrete spallingand reinforcement bar exposure at the end ofthe testing. The framing members – beamsand columns – remained relatively intactthroughout the test. Figure 3 shows theultimate failure state for specimen C4B.

Discussion of test results

The column shear force versus total story drifthysteresis loops for specimens C1B and C4B

are shown in Figures 4(a) and (b). It isobserved that both the hysteresis loopsdisplay gradual strength deterioration. Thisis different from what had been expected, thatis the column shear strength would dropcatastrophically once it reached the peak. It isalso observed that very severe pinching isobserved in the hysteresis loops especiallyafter the drift ratio of 1.5%. This is incontrast to the behaviour of a ductile beam-column joint, for which the hysteresis loopsdepicting the behaviour of column shearversus story drift are supposed to have aspindle shape representing more desirableenergy dissipation behaviour.

The column shear strength envelopes areplotted in Figure 5(a) for the comparisonbetween specimens with axial load C1A andwithout axial load C1B. Figure 5(b) showsthe difference between specimens C1B andC4B, where C1B had a 16% larger jointvolume and a 25% larger anchorage length forbeam main bars passing through the jointpanel.

Loading

Beam End Deflection

mm%

0.00

0.50

1.00

1.50

2.00

2.50

3.00

-0.50

-1.00

-1.50

-2.00

-2.50

-3.00

13.50

27.00

40.50

54.00

67.50

81.00

-13.50

-27.00

-40.50

-54.00

-67.50

-81.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

To actuator stroke limit

Cycle

Figure 2 Loading history

Figure 3 Failure state of specimen C4B

-250

-200

-150

-100

-50

0

50

100

150

200

250

-4.0 -3.0 -2 .0 -1.0 0.0 1 .0 2.0 3.0 4.0

To tal S to ry Drift (rad ian % )

Co

lum

n S

hea

r (k

N

Figure 4(b) C4B hysteresis loops

-250

-200

-150

-100

-50

0

50

100

150

200

250

-4.0 -3.0 -2.0 -1 .0 0.0 1.0 2.0 3 .0 4.0

Tot al St ory D rift (radian %)

Co

lum

n S

hea

r (k

N)

Figure 4(a) C1B hysteresis loops


3

In Figure 5(a), it is observed that althoughthere is no effect on column shear strength,column compressive axial load could lead tohigher stiffness in the early loading stage.Hence, it caused the peak to occur at smallerdrift ratio. The column compressive axial loadin specimen C1A had accelerated the peak tooccur by 45% compared to C1B.

Figure 5(b) shows that specimen C1B hadsignificantly higher peak column shearstrength than C4B. However, specimen C1Bdegraded faster than C4B after the peakstrength. This is believed to be due to therelatively larger bond stress built up inspecimen C1B. A higher bond stress betweenconcrete and reinforcing bar definitely leadsto a higher bond demand. Although C1B hada relatively better anchorage condition thanC4B, the anchorage lengths in both of theselightly reinforced joints were far below thecode requirement. For instance, compared tothe modern seismic design codes NZS 3101-1995 and AIJ-1994, ACI 318-99 has the mostlenient requirement on the anchorage length,

and it requires the ratio of hc/db not to be lessthan 20. Therefore, after the peak columnshear strength was reached, the available bondcapacity in both C1B and C4B was believedto be very low, and C1B with the higher bonddemand definitely resulted in a more rapidstrength degradation.

The induced maximum joint shear stresseswere 6.14, 6.34, 6.47 and 6.27 N/mm2 forspecimens C1A, C1B, C4A and C4Brespectively. According to the ACI 318-99design code, the allowable joint shear stress is1.25√fc

’ for ductile joints, where fc’ is the

concrete compressive strength. This limit wascalculated to be 6.1 N/mm2 in this case,hence, the maximum joint shear stress in thisseries of lightly reinforced beam-columnjoints even reached the limit for ductile joints.However, neither beams nor columnsachieved the yielding capacity.

Conclusions

This series of lightly reinforced beam-columnjoints experienced severe stiffnessdegradation, but relatively gradual strengthdegradation under reversed cyclic loading.The column axial load with the magnitude of15% column squash capacity stiffened thebeam-column sub-assemblage before the peakcolumn shear strength was reached.However, it had insignificant influence on themagnitude of the peak column shear strength.On the other hand, better anchorage conditionacross the joint panel apparently led to ahigher peak column shear strength. Finally,all specimens reached the allowable jointshear stress limit by the design code ACI 318-99 for ductile beam-column joints.

-250

-200

-150

-100

-50

0

50

100

150

200

250

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0

T otal Story Drift (radian %)

Col

umn

She

ar (

kN)

C1A

C1B

Figure 5(a) Specimens C1A and C1Bcolumn shear strength comparison

-2 50

-2 00

-1 50

-1 00

-50

0

50

1 00

1 50

2 00

2 50

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0

T otal Story D rift (radian % )

Co

lum

n S

hea

r (k

N)

C 1B

C 4B

Figure 5(b) Specimens C1B and C4Bcolumn shear strength comparison


Ground Motions Recorded in Singapore during the Bengkulu, SouthernSumatra, Earthquake (Ms = 8.0) on 5 June 2000

T-C Pan ([email protected])K Megawati ([email protected])J M W Brownjohn ([email protected])C L Lee ([email protected])

Main shock and aftershocks

A great earthquake with a magnitude of Ms = 8.0 (according to the United States GeologicalSurvey) occurred in Southern Sumatra, Indonesia, on June 4, 2000, at 16:28:25.8 UTC (June 5,2000, 00:28:25.8 Singapore Time). According to the USGS National Earthquake InformationCentre, the epicentre was located at 4.773o South Latitude and 102.050o East Longitude, under theIndian Ocean, about 110 km off the western coast of Bengkulu Province in Sumatra Island. Theepicentre was about 540 km west-northwest of Jakarta and 700 km south-southwest of Singapore,as shown in Figure 1. The focal depth was reported to be shallow. The tremors from the earthquakewere reportedly felt as far as in Jakarta, Singapore and Kuala Lumpur (875 km North of theepicentre).The earthquake was followed by more than 1,800 aftershocks as of June 11, but only about 50 ofthem could be felt by local residents. Aftershocks that had large magnitudes were collected from theUSGS National Earthquake Information Centre and the epicentres are plotted in Figure 1. Twoaftershocks, on June 4 at 16:39:45 UTC (mb = 6.6) and on June 7 at 23:45:26 UTC (Ms = 6.7), werereportedly felt in Jakarta and Singapore.

Damage in Bengkulu and Enggano Island, Indonesia

Bengkulu is one of the eight provinces in Sumatra Island. This small province is located on thewestern coast of southern Sumatra and has a population of about 1.2 millions. This province was theworst hit area due to its closeness to the epicentre. According to official reports on June 11, ninetypeople were confirmed dead, 803 people badly injured and 1,782 people lightly injured. Most of thedeaths and injuries were due to falling debris from collapsed houses. At least, 122,000 people wereleft homeless.According to an official assessment report of June 11, 1,800 houses were totally destroyed, 10,196houses were heavily damaged and 18,378 houses were lightly damaged by the earthquake. Most ofthe houses were non-engineered, traditional wooden and masonry structures. Severe structuraldamages to engineered structures occurred to only a few buildings. The local airport was closed foroperations due to failures in navigation systems and power generators. Several roads built onswamp areas showed signs of subsidence and cracking at 26 locations. Subsidence of theapproaches to several bridges was also reported. Electricity and water supplies in Bengkulu andsurrounding areas were also knocked out. Only 20% of electricity supply and 25% of water supplywere in service after the earthquake. Widespread telephone line disruptions were also reported. TheIndonesian Meteorological and Geophysical Agency assigned the seismic intensity in Bengkulu tobe V and VI in the Modified Mercally Intensity (MMI) scale of 12.Enggano Island, with a population of 1,686, is only a few kilometres away from the epicentre.Ninety percent of the homes there were reported to have been badly damaged, but no death wasreported. Most of the houses were simply constructed huts, which are incapable of killing theinhabitants when they collapse.


Public and building responses in Singapore

“Tremors hit several parts of Singapore” was the headline in several Singapore newspapersfollowing the earthquake. According to The Straits Times, Singaporeans were awakened from theirsleep by strong tremors, which shook many parts of the island in the early morning of June 5. Thoseliving in high-rise apartments rushed downstairs, still dressed in their pyjamas. The tremors startedbetween 00:30 a.m. and 00:45 a.m. in the east and spread to the north and west. The areas where thetremors were felt are shown in Figure 2, which indicates that virtually the whole island was shaken.Almost all of those who perceived the tremors lived in high-rise buildings. The tremors felt werethe main shock and the major aftershock that occurred 11 minutes afterwards. No one was injuredby the tremors.The second round of minor tremors hit Singapore on June 8, at 7:48 a.m., but they caused no alarm.The tremors came from an aftershock that hit southern Sumatra and was measured at Ms = 6.6. Thetremors were felt mainly in Chinatown, Marine Parade, Meyer Road, North Bridge Road, CrawfordLane and Bishan. No injuries were reported.

Seismic instrumentation and ground motions recorded in Singapore

In 1996, the Meteorological Service of Singapore installed a network of seismic stations, whichconsists of two down-hole arrays of strong motion stations and five teleseismic stations. Thelocations of the stations are depicted by triangles in Figure 3. The two down-hole arrays, denoted asBES and KAP, are located on the Kallang Quaternary deposits. The main station in the Bukit Timahnature reserve, denoted as BTDF, is a Global Seismic Network station, which is equipped with acomprehensive set of sensors to record ground tremors continuously. BTDF is located on a rockoutcrop site.The Nanyang Technological University (NTU) has also installed two additional seismic stations,one inside the campus (denoted as NYC) and the other in the basement of a high-rise office buildingin the city centre (denoted as RP). The NYC station is located on a firm residual soil site, and thebuilding in which the RP is located sits on rigid caissons. The two NTU and seven MSS stations

92 94 96 98 100 102 104 106 108

-10

-8

-6

-4

-2

0

2

4

6

8

Lampung (IV)

Padang Jambi

Palembang(III-IV)

Siberut

67 mm/yr

Batu

Sumatra F.

Mentaw

ai F.

Subduction Zone

500 km0

Enggano

Nias

Penang

Ipoh (Perak)

Jakarta (II-III)

Bengkulu (V-VI)

Medan

Melaka

Kuala Lumpur

Singapore (III-IV)

aftershocks (up to 07/16)

mainshock

Figure 1. Epicentres of main shock and largeaftershocks, as of July 16, and seismic intensitiesin MMI scale assigned for big cities in the region

Figure 2. Locations of Singapore buildings reportedlyresponding to the Bengkulu earthquake


form an array called the Singapore Array for Earthquake Response (SAFER), which was proposedjointly by NTU and USGS.The two NTU stations and one of the MSS stations (BTDF) were triggered during the Bengkuluearthquake. Ground motions from the main shock (2000/06/04 16:28:25 UTC) and the two majoraftershocks (2000/06/04 16:39:44 UTC and 2000/06/07 23:45:26 UTC) were successfully recorded.Figure 4 show the baseline-corrected accelerations recorded during the main shock. In the figure,the top three traces are the E-W, N-S and U-D components recorded at BTDF. The following threetraces are the components recorded at NYC, and the bottom two traces are the horizontalcomponents of the RP station according to the two principal axes of the building.

Discussions

Building responses to earthquakes are dependent upon the building type and the ground conditionwhere the building stands. From 1971 to the time prior to the Bengkulu earthquake, there had been10 earthquakes in Sumatra that caused tremors felt in Singapore (Pan and Sun, 1996). It wasreported that only high-rise buildings in the central and south-eastern parts, which are underlain byQuaternary marine clay deposit (Pitts, 1984), were shaken in these events. The soft sedimentarydeposit might have amplified the weak bedrock motions to a level that caused the buildings tovibrate perceivably.However, the Bengkulu earthquake shook many high-rise buildings across almost the wholeSingapore. The fact that the locations of the buildings were widely distributed throughout the islandindicates that the earthquake, which was the largest in recent decades, generated large enoughground motions to cause perceptible level of vibrations to residents of the buildings, regardless ofthe local soil condition.

References

[1] Pan, T.-C. and J. Sun (1996). Historical earthquakes felt in Singapore, Bull. Seism. Soc. Am. 86,1173-1178.

[2] Pitts, J. (1984). A review of geology and engineering geology of Singapore, Quarterly Journalof Engineering Geology 17, 93-101.

Figure 3. Seismic stations in Singapore (SAFER Array)

Figure 4. Baseline-corrected accelerations of the mainshock (2000/06/04 16:28:25 UTC) of the Bengkuluearthquake, recorded in Singapore


Adaptive Surface Mesh Generation

C K Lee ([email protected])Y K Lee([email protected])

Introduction

An adequate discretization of a surface is one ofthe most difficult and important prerequisitesfor 3D mesh generation and finite elementmodelling of shell structures. An automaticmesh generator that can generate high quality,well-graded surface meshes with element sizecompatible with the user specification will be anindispensable tool for general shell and 3Dfinite element analyses. In this article, thetechniques and procedures for the discretizationof general 3D surfaces, which may be seriouslyfolded, into triangular mesh will be described.In addition, the procedure to convert thetriangular mesh to a full quadrilateral mesh willbe outlined. The triangulation and quadrilateralmesh conversion schemes described here can beused to generate well-graded anisotropic finiteelement meshes with element size distributioncompatible with the user input specification.

Metric surface triangulation

The main mesh generation technique used hereis the metric advancing front technique whichhas been successfully used in 2D meshgenerations. The geometrical model usedregards the target surface to be meshed as ageneral bi-variate mapping defined as

v)(u,=z)y,(x, rT(1)

Hence, the relationship between dx and du, theelementary vectors in the 3D and parametricspaces respectively, is given by

( )durrdx vu , ,,=dv

du

v

z

u

zv

y

u

yv

x

u

x

=

dz

dy

dx

=

∂∂

∂∂

∂∂

∂∂

∂∂

∂∂

(2)

In the 3D space, ℜ 3, the metric tensor thatdefines the user specification of element sizecharacteristics can be written as a 3×3 matrix,M3D, of the form

λλ

λ

3

2

1

3

2

1

3

2

1

3D

00

00

00

=

fed

ecb

dba

=

e

e

e

e

e

e

M

T

(3)

such that Det(M3D) > 0. In Equation 3, (ei,λ i),i=1,2,3 are the eigenpairs of M3D such thatei⋅⋅⋅⋅ej=δij and λ i=1/(hi)

2>0 where hi is theprincipal element size in the ei direction. Theeigenpair, (ei,λ i), will determinate the stretchingratio and direction of the mesh. By using themetric tensor the distance between two points P1

and P2, ),( 213D PPM~l , is defined as

∫1

0

213D213D dtt)),,((=),( QPPQMQPPM~ Tl (4)

where

Q P P P P P( , , t) = + t( - ) 0 t 11 2 1 2 1 ≤ ≤ (5)

Thus, the length of an elementary vector, dξξξξ, inthe normalized space can be expressed as

dxMdxdd~

3D2 = TT ξξξξξξξξ=l (6)

By combining Equation 2 with Equation 6, therelationship between dξξξξ and dx can be writtenas

( ) ( )duMdu

durrMrrdu

dxMdxdd~

vuvu

sur

3D

3D2

,,,,T

TT

TT

=

=

== ξξξξξξξξl

(7)

Thus, the 2×2 matrix, Msur, defined as

( ) ( )M r r M r ru v u vsur 3D= , , , ,T

(8)

is the metric tensor which combines the effectsof the user specification and the surfacemapping.

With the surface metric tensor defined, a metricadvance front mesh generation scheme, which issimilar to the one used in 2D problem, can beused for element generation in the normalizedspace so that the operation complexity of the


generation procedure is equal to that of the 2Dcase. The finite element mesh will be generatedin a hierarchical bottom up (point-curve-surface) sequence which involves three maingeneration stages(1) control point formation(2) boundary segment generation, and(3) surface mesh generation.

After the above three main generation steps arecompleted, the quality of the triangular meshwill be further improved by some standard meshquality enhancement schemes.

Quadrilateral mesh conversion

As the performance of quadrilateral elements isgenerally superior to that of their triangularcounterparts, a mesh converter which is able toconvert a pure triangular mesh into a purequadrilateral mesh is included in the meshgeneration program. It will directly accept theoutput from the triangular mesh generator andconvert the mesh to a pure quadrilateral mesh.The mesh conversion algorithm used is anenhanced and extended version of thesystematic merging technique developed in thepast for 2D isotropic quadrilateral meshgeneration. The basic principle for conversionlies in the fact that a triangular mesh consistingof an even number of triangles can always beconverted into a complete quadrilateral mesh bya series of carefully controlled merging andsubdivision operations. Special new procedureshave been developed and implemented to ensurethe quality and preserve the grading andanisotropic property of the input surface mesh.

Meshing examples

Two meshing examples are given here todemonstrate the performance and effectivenessof the mesh generation and conversion schemesdescribed. In the first example, a multi-connected surface domain corresponding to thelogo of the Computational Mechanics (CoM)Research Group, School of Civil and StructuralEngineering, NTU is used. An isotropic 3Dmetric tensor is used to define a rapidly gradedmesh over the problem domain with small size

elements around the internal openings. Thetriangular mesh generated is shown in Figure 1aand it is then fed into the mesh converter for thegeneration of a complete quadrilateral mesh.The intermediate mesh with 1500 quadrilateralelements generated and the final fullquadrilateral meshes produced are shown inFigures 1b and 1c respectively. From Figure 1c,it can be seen that the density of the elements iswell preserved.

Figure 1a. Example 1, CoM logo, triangularmesh

Figure 1b. Example 1 CoM logo, mesh after1500 quadrilaterals are generated

Figure 1c. Example 1, CoM logo, finalquadrilateral mesh with 3883 nodes and 2788elements


In the second example, part of a cylinder isconsidered. In this case, an aniostropic metrictensor is used such that rapidly gradedanisotropic elements are formed along part ofthe top edge of the cylinder. The triangularmesh, the intermediate converted mesh and thefinal full quadrilateral meshes generated areshown in Figures 2a, 2b and 2c respectively. Inaddition, zoomed views of the rapidly gradedand ansiotropic regions are shown in Figures 3aand 3b for the triangular and the quadrilateralmeshes respectively. Once again, it can be seenthat well-shaped elements are generated and theelement size distribution of the input triangularmesh are well preserved even at the rapidlygraded and anisotropic region of the mesh.

Figure 2a. Example 2, Cylinder, triangular mesh

Figure 2b. Example 2, Cylinder, mesh after 400quadrilaterals generated

Figure 2c. Example 2, Cylinder, finalquadrilateral mesh with 833 nodes and 782elements

Figure 3a. Example 2, rapidly graded andanisotropic region near the top for the triangularmesh

Figure 3b. Example 2, rapidly gradedanisotropic region near the top for the finalquadrilateral mesh


Detection of Cracks Through Changes of Vibration Frequencies

S C Fan ([email protected])D Y Zheng ([email protected])

Cracks found in structural elements havevarious causes. In concrete structures, itcould be the opening of dry-joints betweenprecast elements, in particular in thosesegmental-constructed box-girder bridgesassembled with dry joints that are favoured intropical countries.

Dimarogonas[1] presented the state-of-artreview of various methods in tackling thecracked-structure problem.Recently, Shifrin and Ruotolo[2] developed amethod that can be used to tackle a beamwith multiple cracks. However, their studieswere limited to Euler beams.

This paper describes a new methoddeveloped for computing the naturalfrequencies of a Timoshenko beam with anarbitrary number of transverse open-cracks.The essence of this new method lies in theuse of a kind of Modified Fourier Series thatis developed specially for the analysis of abeam with arbitrary number of transverseopen-cracks. Unlike the conventionalFourier series, the modified series is able toapproach a function with internalgeometrical discontinuities effectively.Based on the present Modified FourierSeries, one can treat the cracked beam in themost usual way and thus reduces theproblem to a simple one.

Theory and formulationModified Fourier series Ym(y)Consider a beam having (Q-1) number oftransverse open-cracks located at y = y2, y3,…, yQ and having N point-spring supportslocated at y = s1, s2, …, sN respectively. Thebeam can have non-uniform cross-sectionalareas A(y) and various second moment ofarea I(y) along the longitudinal direction y.The depths of the cracks are: {ai, i = 1, 2, …,Q-1}, 0≥ia , and the translational-and-

rotational stiffness of the point-springs are:{ki, χi, i = 1, 2, …, N}.

The transverse deflection and the rotation ofcross-section of the Timoshenko beam aredenoted by w(y, t) and ),( tyψ respectively,where y stands for the location and t standsfor the time. Considering the continuity offunction w(y, t) and discontinuity of function

),( tyψ , we can express them as follows:

)()()()(),( 11

tyyYtwtywR

mmm qH== ∑

=

(1)

)()()()(),( 21

tyyYttyR

mmm qH== ∑

=ψψ (2)

In the above equations, )(yYm is the Fourier

series base function (Liu, Zheng & Mei[3])and Ym(y) is the so-called modified Fourierfunction which is specifically constructedsuch that it can approach a function withinternal discontinuities:

)(~

)()( yYyYyY mmm += (3)

( )( )

=+===

==

rkkmyk

rkkmyk

m

yYm

..., 2, 1, 1;2 sin

..., 2, 1, ;2 cos

1 1

)(

0

0

ωω

(4)in which 2r+1 = R.

∑=

=Q

jjjm ylfyY

1

)()(~ (5)

where l/0 πω = (l is the length of the beam)

is the basic frequency and lj(y) are the piece-wise constant-interpolation base functions:

( ) ∈

= +

others

yyyyl jj

j ,0

, ,1)( 1

(6)

By adding the piece-wise constant functions{ )(

~yYm

, m = 1, 2, …, R} onto the basic

Fourier series { )(yYm, m = 1, 2, …, R}, we

can force the whole function {Ym(y), m= 1, 2,…, R} to satisfy the geometrical


discontinuity conditions at the locations ofcracks. Thus in the following analysis, wecan treat the cracked beam in the most usualway and need not further bother about theinternal geometrical discontinuities.The geometrical discontinuity condition atthe cracks’ location y = yj (j = 2, 3, …, Q) is:

)()0()0( 1 jmjjmjm yyYcyYyY →′=−−+ − (7)

where cj-1 is the flexibility coefficient of thecrack having a depth of aj-1. The values of cj-1

given by Haristy and Springer[4] are adopted.

Energy analysisThe potential energy of a crackedTimoshenko beam under axial-load can beexpressed as the summation of the followingfive parts:

54321 UUUUUU ++++= (8)

in which U1 and U2 are the potential energystored in the cracked beam due to bendingand shearing deformation of the beam itself;U3 is the potential energy stored in the point-springs which are used to model theboundary supports and also the intermediatesupports (if any); U4 is the potential energystored in the massless rotational springswhich are used to model the existence ofcracks; U5 is the potential energy of theexternal variable axial load )( yNλ .The kinetic energy of the Timoshenko beamcan be expressed as the summation of the twoparts, T1 and T2, such that,

21 TTT += (9)in which T1 and T2 are the kinetic energystored in the Timoshenko beam due totranslational and rotational deformationrespectively.

Euler-Lagrangian equationsThe Euler-Lagrangian equations of thecracked Timoshenko beam are:

0qq

=∂∂−

∂∂

11

LL

dt

d!

, 0qq

=∂∂−

∂∂

22

LL

dt

d!

(10-11)where L is the Lagrangian function.Substituting relevant equations into Euler-Lagrangian equation, we have

( ) 0qKqKKKqM =−−++ 2221312111 Gλ!!

( ) 0qKqKKKKqM =−++++ 122243223122T!!

(12-13)Equations (12) and (13) can be written intoone matrix equation,

0KqqM =+!!

(14)where

=

2

1

M0

0MM (15)

+++−

−−+=

43223122

223121

KKKKK

KKKKK T

Gλ

(16)

=

2

1

q

qq (17)

ExampleConsider a two-span continuous girder builtby segmental construction method. The totallength of the bridge is l=2x33=66m,composed of 2x10=20 segments. The 20segments are held together via longitudinalpre-stressing force. Joints between segmentsare dry-joints (i.e. no cement mortar). It has aconstant cross-sectional area A=1.9892m2,second moment of area I=0.8804m4, anddepth h=1.9m. The pre-stressing force is anaxial force F=10MN without eccentricityfrom the centroidal axis. Young’s modulus istaken as 20GPa and the Poisson’s ratio is 0.2.The first crack’s location varies from theleftmost segment-joint to the rightmostsegment-joint in the left span and the depth isa1=0.75m. The second crack is sited at afixed location in the mid-span of the rightspan (yc2=49.5m) and has a fixed deptha2=0.25m. The results are shown in Figure 1,which shows the effect of the unexpectedopening of dry-joints on the naturalfrequencies of the segmental girder.

SummaryA new Modified Fourier Series (MFS) waspresented. It was developed to tackle theproblem in beams with arbitrary number ofcracks. The Modified Fourier Series can


approach a function with internal geometricaldiscontinuities effectively. Via the Euler-Lagrangian equation, we can treat thevibrational analysis of a cracked beam in themost usual way. It thus renders the problem-solving procedures simple. In theformulation, an open-crack assumes havingstiffness, which is simply added to thestiffness matrix of the beam. The beam canbe of non-uniform cross-section and thenumber of cracks can be arbitrary. In solvingthe natural frequencies of a cracked beam,only a standard linear eigen-value equationneeds to be solved. All the formulae areexpressed in matrix form and thereforecomputer coding is straightforward.Numerical examples show that the presentmethod is versatile and effective.

Reference[1] Dimarogonas, A. D., (1996).

Vibration of cracked structures: astate of the art review. EngineeringFracture Mechanics 55, 831-857.

[2] Shifrin, E.I. and Ruotolo,R., (1999).Natural frequencies of a beam with anarbitrary number of cracks. Journal ofSound and Vibration 222, 409-423.

[3] Liu, J.Y., Zheng, D.Y. and Mei, Z.J.,(1995). Practical Integral Transformsin Engineering (in Chinese),Huazhong University of Science andTechnology Press.

[4] Haristy, B.S. and Springer, W.T.,(1988). A general beam element foruse in damage assessment of complexstructures. Journal of Vibration,Acoustics, Stress and Reliability inDesign 110, 389-394.

Figure 1. Effect of location of the first crack on the frequency ratios (a1=0.75m, a2=0.25m, yc1 varies and yc2=49.5m)

0.970

0.975

0.980

0.985

0.990

0.995

1.000

3.30 6.60 9.90 13.20 16.50 19.80 23.10 26.40 29.70

yc1

1st frequency ratio

2nd frequency ratio

3rd frequency ratio

ω ωωω /

ω ωωω0


Structural Health Monitoring using Smart Materials

Kevin K H Tseng ([email protected])C K Soh ([email protected])

Abstract

In recent years, structural health monitoring has become an important requirement incivil engineering, especially in the densely populated areas such as many Asian cities.Various monitoring techniques have been proposed and studied. This paper will focuson the application of the piezoceramic transducer (PZT) patches on the healthmonitoring of civil infrastructure. This technique is non-destructive in nature and thewide range of the excitation frequency (from a few Hz to a few MHz) enables thistechnique to capture structural damage from small to large scale. Other importantadvantages of this technique include its cost effectiveness and the ease of applicationin practical civil infrastructures. Therefore, it is a promising technology for furtherresearch, development, and even commercialisation.

Introduction

Traditional construction materials in civil engineering are basically passive in terms ofresponding to the applied loads. The strength of these materials is fixed and will notchange during the lifetime of the structures except from degradation. In recent years,a new type of material has been developed to overcome this constraint. The so-calledsmart materials refer to the class of materials that are capable of reacting to certainexcitation. This paper will discuss the results and experience of applying the smartPZT patches to the health monitoring of civil infrastructures.

When the PZT patches are excited by a given AC electrical current with a certainfrequency, a mechanical vibration will be created. The vibration will generate elasticwaves into the materials. These waves will serve as the detector for any material andstructural damage. Simultaneously, the dynamic response from the material willaffect the vibration mode of the PZT patches. The response will then cause theconductance of the PZT patches to change. This special feature of the smart materialenables the PZT patches to serve as both actuator and sensor.

Regular health monitoring of civil infrastructures is of considerable importance inview of the immense loss of life and property that may result from their failure. ThePZT patches, attached to the surface of the structure, are electrically excited, and thereal part of electrical admittance (conductance) is extracted as a function of theexcitation frequency. An Impedance Analyzer is used to scan the patches over acertain range of frequency for the acquisition of the signature. The deviation of thesignature from that recorded for the healthy state provides an indicator of the health ofthe structure. The damages can be quantified in non-parametric terms using root meansquare deviation in signatures with respect to the baseline signature of the healthystate.


Damage quantification

Based on the data collected from various experiments including tests on steel beams,aluminium plates, concrete cubes, and some prototype RC structures conducted in theSchool of Civil & Structural Engineering (CSE), Nanyang Technological University(NTU), many different damage indices have been investigated. The Root MeanSquare Deviation (RMSD) has been found to be an effective index for the changes inthe signatures due to structural damage. The results for a prototype bridge arepresented in the following section.

Application to the prototype RC bridge specimen

The test structure was a single-span girder bridge made of reinforced concrete with aneffective span of 4.85m. It consisted of two longitudinal beams with 250mm in depth,which supported a deck slab of 100mm in thickness. A picture of the bridge is shownin Figure 1. It was constructed by the second year undergraduate students of theSchool of CSE, NTU, as part of their 1999 In House Practical Training (IHPT 1999).

The test structure was instrumented with PZT patches, each of size 10mm by 10mmwith 0.2mm in thickness, and attached to the structure at various locations. Thebridge is subjected to progressive loading up to the service limit. The PZT patchattached at the tensile stress zone at the bottom of the face of the bridge is located nearthe centre of the span where the damage is likely to be initiated. Figures 2 shows therelationship between the calculated damage index and the applied load at the top faceof the bridge. It is observed that just prior to the structural failure, there is an abruptincrease in the damage index.

Figure 1. Test bridge under loading


Ongoing and future research and development

With the goal of constructing a commercially feasible solution for practical civilengineering applications, more research and development works are being undertakenin the School of CSE, NTU, including the investigation of the effects of temperatureand dampness variation on this technique, applying an array of PZT patches toaccurately predict the location, size, and evolution of the damage in the structures, andthe study of the effect of a variety of loading conditions. In addition to theexperimental work, numerical and analytical modelling are being conducted to fullyunderstand the mechanism of this technique.

Conclusions

Smart materials, as compared to the conventional civil construction materials, havethe superior capability of reacting to the external excitation by changing the materialparameters including the strength of the material. This special feature can be appliedto perform the health monitoring of the civil infrastructures. The smart PZT patchescan be attached to the surface of the structure to serve as both actuator and sensor.Experimental results have shown that this technique is capable of predicting structuraldamage via the selected damage index. Since the technique is non-destructive andeasy to apply to existing structures, it is a promising tool for structural healthmonitoring. In addition, the technique is low-cost and can be developed into acomprehensive system for commercialisation.

Figure 2. RMSD(%) at various loading stages

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60

Load (KN)

RM

SD

(%)


SURVEYING

Real-Time Traffic Monitoring System Using Web-based GIS and Multimedia TechnologyPC Goh ([email protected])

YS Phan ([email protected])

IntroductionThe application of information science andtechnology in the transportation industry hasbrought about numerous advancements in areaslike traffic management, traffic flowmonitoring, and vehicle routing and tracking,among others. A recent study of the 75 mostcongested metropolitan areas of the UnitedStates showed that well designed ITinfrastructure would generate an overall benefit-to-cost ratio of about 8 to 1. The powerfulinformation management capability of web-based GIS could be deployed to mitigate traffic-related challenges like traffic bottlenecks andincident management while working as aninformation service.

Traffic accidents, flow, volume, road networkand road furniture are geographic entities thatrequire proper representation and can berepresented by one easily understood format – adigital map. Data captured from the presentadvanced traffic management systems can bemore easily accessed and related to spatialinformation to perceive patterns andrelationships through a web-based GIS. Thesepatterns and relationships are not so apparentwhen the data resides in a conventional table orspreadsheet of database management system. Inaddition, the flexibility and maneuverability ofvarious geo-referenced data has provided trafficprofessionals with greater support in makingtimely decisions that have improved road safetyand reduced traveling time. Hence,transportation applications of GIS have becomeincreasingly popular in recent years and arenow being referred to by the acronym GIS-T.

This project investigates the potential ofincorporating multimedia in a web-based GIS toenhance data communication and

representation, with relatively low costsystem architecture.

Figure 1. The components of the prototype

Development of PrototypeFor this prototype, a web site wasdeveloped utilizing web-based applicationserver software known as Cold FusionTM

Server to host the overall system. Throughthis real-time GIS system, trafficinformation is disseminated to local users oran Internet user in the form of real-timedigital video streams, location maps andintegrated reports. The hardwarecomponents of the prototype are shown inFigure 1.

Traffic parameters are extracted from aVideo Image Processing Software (VIPS)known as CCATS® (Camera andComputer-Aided Traffic Sensor byTRAFICON) and these raw data are savedas text files in the server’s local directory. Aprogram was developed to extract (read)raw data from the text file and populate(write) a designated database with thesedata. Active Server Page (ASP) (a smallembedded program) is used to drive thedata from a database into the user’sbrowser. Typically, the script in the webpage at the server uses input received as a


result of the user's request for the page to accessdata from a database and then builds orcustomizes the page on the fly before sending itto the requester. (A schematic diagram in Figure2 illustrates the details)

Figure 2. A schematic diagram of the basiccomponents of the prototype system

Implementation issuesThe two primary challenges that must beaddressed before implementing this prototypeare project funding and the determination of thetechnologies to be adopted. The funding methodwill determine the choice of technology fordisseminating traffic information. Thetechnology adopted will in turn impact on thenumber of users and hence determine thecommercial viability of the system.

There are several ways of funding thisprototype system. It can be funded through thepublic sector, a public/private partnership or bya private venture. Since this prototype system ismeant to be available free of charge to thepublic, it can be implemented with the currentavailable Internet web technology if publicfunding to do so is available.

Web-based GIS is undergoing a tremendousevolution and the only constant is change. In thelate 80s, users were satisfied if they could justview a map. During the 90s, they required livemaps to be served upon request bundled withdatabase interactions and spatial analysis.Recently, efforts have been made to deliver livedata over the Internet through a GIS. In short,the demand for timely traffic information andanalysis will affect the overall picture of thefuture of Internet GIS.

Commercial application of the prototypeA major potential group of users of theprototype would be daily road users, freightoperators and other commercial fleetoperators within city precinct. Thisprototype would provide value-addedservices to many sectors, in particular,traffic monitoring. A direct access throughthe Internet [either by fixed lines or WAPtechnology] would definitely provide roadusers with more detailed traffic information.This would enable users to make aninformed decision to improve their traveltime.

Conclusions and commentsEven though web technologies areconstantly changing and evolving veryrapidly, we can still tap in to the existinginfrastructure to provide value-addedservices to many sectors, in particular,traffic monitoring. Based on the prototypepresented, multimedia is a definiteenhancement alternative for providing aneffective means of communicatinggeographic data, in particular traffic data,through a comprehensive web-based GIS.

References

[1] Phan, Y.S. (2000). “Real-TimeTraffic Monitoring Using GIS andMultimedia Technology,”Proceedings of the 26th

International Traffic RecordsForum, Portland, Oregon, USA.

ClientComputer

www browser

Server Computer

HTTP server Map generator

Webcam32software

GIS Software GIS DataWebcam32

software

InternetMap

ImageCCATS


Low-Cost, High-Accuracy GPS PositioningSystem Utilising Multiple Reference StationNetworkP C Goh ([email protected])S T Teo ([email protected])

IntroductionThe NAVSTAR Global Positioning System(GPS) is a satellite-based radio navigation andpositioning system developed and operated bythe United States Department of Defense(DoD). Being continuously available, highlyreliable, weather independent and free ofusage charge, GPS has gained increasingpopularity among the civilian community as aconvenient and efficient positioningtechnology and has been utilised in manydifferent types of applications. With suitableequipment, users are able to positionthemselves with respect to either a worldgeodetic reference frame (point positioning) orwith respect to a known point within a localcoordinate system (relative or differentialpositioning).

The accuracy obtainable from the use of asingle code-measuring GPS receiver in pointpositioning mode (typical of general-purposenavigation applications) ranges from around5m to 50m. On the other hand, a phase-measuring receiver in differential positioningmode is capable of providing sub-metreaccuracy at all times even when used forkinematic applications. Hence, for applicationsthat require sub-metre accuracy, differentialpositioning must be applied using phase-measuring receivers. Such receivers, togetherwith commercial software necessary forprocessing the measurements, are highlyexpensive and have not been widely adoptedby surveying and mapping users for routineuse.

The Singapore Integrated MultipleReference Station Network (SIMRSN)With the current development of the SingaporeIntegrated Multiple Reference Station Network(SIMRSN) infrastructure (Figure 1), highpositioning accuracy may potentially beobtained using low-cost, single-frequency,

phase-measuring GPS receivers. The benefitsof the SIMRSN approach include furtherallowable rover-reference station separation,faster time to ambiguity resolution,improvements to relative positioning accuracyas well as higher integrity of overallperformance. Another significant benefitinvolves the reduction of users’ costs – insteadof the need to own and operate two high-endreceivers, each user requires only one phase-measuring GPS receiver and a means ofcommunication (either wired or wireless) withthe control station of the SIMRSN. In addition,they are freed from the need to purchase high-cost commercial software as the processing ofthe measurements can be performed at thecontrol station. The last two factors cut downthe cost of implementing a GPS-basedpositioning solution significantly and areespecially suitable for users who require onlysub-metre (not millimetre) accuracy in theirapplication.

Figure 1. Singapore Integrated Multiple ReferenceStation Network (SIMRSN)

The proposed low-cost systemThe proposed low-cost system comprises thefollowing components:i) a single-frequency, phase-measuring GPS

receiver,ii) a mobile computer (PDA or laptop or

equivalent),iii) software running on mobile computer,

GPS reference stations linked by lease lines tocontrol station

Control station with communication equipment

Legend

Rover with wired/wireless link to control station


iv) communication device operating onmobile computer,

v) communication device operating atSIMRSN control station, and

vi) software running at SIMRSN controlstation.

Components i) to iv) form the basicconfiguration of a typical roving station. Otherthan the above components, the system willalso make use of the SIMRSN with itsimplementation of the network data processingalgorithm, as well as a wireless data networkfor data communications between the rovingand the control stations. Figure 2 illustrates theinteraction between the various components ofthe proposed system whereby processing ofmeasurements are performed at the controlstation.

Figure 2. Interaction among system components

Current developmentsSoftware for the roving station is currentlybeing developed and the use of GSM (GlobalSystem for Mobile Communications) as themeans of wireless data communications isbeing looked into. Concurrent developmentwork on the SIMRSN is being carried out byfellow researchers from the Surveying andMapping Laboratory.

ConclusionThe development of a low-cost, high-accuracypositioning system would benefit users indifferent types of applications. Surveying andmapping users would improve theirproductivity when capturing location basedinformation. Vehicle tracking and fleetmanagement users would enhance theiroperational efficiency with better knowledgeand control over their fleet movement. Generalnavigation users and emergency vehicledrivers would find it easier to identify theirlocation and to navigate to their destinationwhen the system is supplemented with digitalmaps.

GPS receiver

Communicationdevice

Radio signalsfrom GPSsatellites

L1 and/or L2pseudo-range and

carrier phasemeasurements

Formatted PVTresults from

control station

Input OutputHardware & Software

Display ofPosition, Velocityand Time (PVT)

results

Formattedpseudo-rangeand/or carrierphase data to

control station

Control Station ofSIMRSN (with custom

software andcommunication device)

Roving Station

7

6

5

4

3

21

10

9

8

Mobile computer(with custom

software)


TRANSPORTATION

‘Left Turn On Red’ Traffic Scheme in SingaporeY D Wong ([email protected])Y T H Foo ([email protected])

Introduction

Left-turn-on-red (LTOR) traffic control is a traffic management practice that was first implementedin Singapore in 1997. Under LTOR control, a vehicle is permitted to make a left turn on a red trafficsignal indication, after stopping and giving way to other vehicles and to pedestrians. The scheme isaimed at providing left-turning traffic with increased operational efficiency, especially delaysavings, at a low cost. The LTOR control is operated under a sign-permissive system, and is appliedonly at side-road approaches of T-junctions. There are presently about 50 signalised T-junctionswith the LTOR facility. A study was carried out to evaluate the performance of the LTOR controlfrom three aspects: stopped delay, compliance with mandatory ‘stopping-first’ rule, and before-afteraccident occurrences.

Stopped delay

A ‘before-and-after’ stopped delay study was carried out at four LTOR junctions. The beforeobservations were made shortly before the implementation of the LTOR control, while the afterobservations were performed between 6 to 12 months after implementation. Each observationperiod lasted for a peak hour (5-6 p.m.) on a typical weekday. A significant reduction in stoppeddelay to the LTOR traffic was found (see Figure 1) while the traffic volumes for the differentmovements remained fairly constant in the before and after observation periods.

22

16

24

30

24 3

8

0

10

20

30

A B C DJunction

Before

After

Figure 1. Before and after stopped delay at four junctions


Compliance with mandatory stop before making LTOR

Under LTOR control, it is mandatory to stop first even if there is no conflict. LTOR manoeuvreswere studied for the 5-6 p.m. after period. At the LTOR lanes of the four junctions, a substantialmajority of the arrivals in the red signal indication period were able to execute LTOR withoutconflict. Of these non-conflict cases, a large proportion of the motorists did not come to a completestop before making the left turn (see Figure 2). It is appropriate to mention that the signage forLTOR has since been revised from ‘GIVE WAY’ to ‘STOP Before Turning’.

LTOR Non-Conflict Cases

0

20

40

60

80

100

A B C DJunction

Stop & Turn

Turn w/o Stop

Figure 2. Compliance with mandatory stop before making LTOR (non-conflict cases)

Before-After accident occurrences

Injury accident occurrences were compared for equal before and after durations at 51 LTORjunctions. Within a period of about a year to a year and a half after LTOR implementation, there wasno notable change in traffic safety. The number of accidents remained at about the same level (seeFigure 3) while the accident pattern by injury level and crash type remained about the same.


0

20

40

60

80

0 1 2 3Accident Counts

Before

After

Figure 3. Distribution of 51 LTOR junctions by accident counts

Concluding remarks

Based on the before-and-after studies, it was concluded that a significant reduction in stopped delayto the LTOR traffic was achieved. However, it was observed that a large proportion of LTORmotorists did not comply with the ‘stopping-first’ rule. No significant change in traffic safety wasdetected in the post-implementation period. Further efforts are currently underway to assess theeffects of recent revisions in the LTOR scheme as well as its longer-term impacts.


Modelling of Driver Perception-Response Times at Signalised JunctionsP K Goh ([email protected])Y D Wong ([email protected])

BackgroundAt junctions with traffic signal control, drivers’ right-of-way status is communicated by thesymbolic colour schemes of signal indications - green for right to proceed, and red for prohibitionof entry. The provision of an amber interval following the termination of green gives drivers someamount of time to respond to the loss of right-of-way.

For drivers caught within the junction approach during the onset of the amber indication, those nearthe stop-line can continue into the junction while distant drivers should slow down and come to astop. Drivers in the in-between position may opt to stop with rapid deceleration, or attempt to enterand clear the junction. The success of the stopping manoeuvre is dependent on the perception-response time (PRT) of the driver and the deceleration rate employed. The transportationcommunity usually adopts a design value of 1 second for PRT (ITE, 1994).

The design value was established based on a consideration of findings obtained from controlledexperiments, with limited input from on-site field studies at signalised junctions. The few on-sitefield studies that were conducted tended to yield PRT values higher than the normative designvalue. This discrepancy between the field-observed and design PRT values can be attributed to themanner in which subject drivers were chosen. In particular, it should be noted that earlier studiesdid not make a distinction between forced-paced and free-paced braking. Free-paced brakingapplies to situations where drivers have some leeway before needing to initiate any braking action,such as, when the driver is placed some distance from the stop-line during the onset of amber. Thisinevitably imposes some lag time onto the observed response times. In contrast, forced-pacedbraking requires immediate action. As such, it is more representative of a driver’s ability to respondto signal change and thus, more appropriate for design.

In an earlier investigation of PRT by the authors (Goh and Wong, 2000), a method was proposedthat excludes drivers with a superimposed lag time by restricting subject vehicles to a transitionalzone (TZ). The TZ, an empirically calibrated time domain, contains both stopping and crossingvehicles. It was found that PRT within the transitional zone had a narrower range of values with an85th percentile that was close to the PRT used for design.

A statistical distribution modelling exercise was carried out to fit empirical PRT values obtainedfrom a series of signalised junctions. Knowledge of the underlying PRT distribution is bothimportant and useful for analysing traffic interactions at signalised junctions.

MethodologyVehicles approaching a signalised junction were unobtrusively recorded using digital videoequipment under daytime, dry weather conditions. Two types of movements were chosen: straight-through movements where approaching vehicles could be obstructed by right-turning vehicles fromthe opposite approach (typical of flow at cross-junctions), and straight-through movements withoutany such conflicts (applicable to flow at ‘top’ of T-junctions). Together, they represent two extremesituations in the road system, with one having a high collision risk and the other having a negligiblecollision risk. The number and attributes of the study sites are shown in Table 1.


JunctionType

ApproachesStudied

SampleSize (TZ*)

Cross-jtn 4 109T-jtn 2 89

*TZ-Transitional zone

Table 1. Sample size and location

Data were extracted from video footage for non-platoon vehicles. The information for each subjectvehicle included its position (from stop-line to rear wheel of the vehicle) and speed, at onset ofamber, as well as whether it stopped or crossed the junction. The type of vehicle was also noted. Aprojected time interval was computed (distance÷speed), that represents the travel time required tocover the distance to the stop-line at the prevailing speed. The TZ was used to exclude those driverswith a superimposed lag time to their response. Details on the calibration of the transitional zonehave been presented elsewhere (Goh & Wong, 2000).

The statistical distributionThe observed cumulative PRT with respect to the projected time to the stop-line is plotted in Figure1. The modelled values from this study were fitted using a log-normal distribution (Equation 1).The log-normal probability density function has the form:

( )

:

lnln

2

1exp

2

12

Where

t

ttf

−−=ζ

λπζ

meandevStd

medianPRTt

==

+=

==

µσ

µσζ

λ

..

1ln2

2

Equation 1. The log-normal distribution

It can be seen from Figure 1 that the log-normal distribution is able to fit the observed PRT valuesfairly well (within 1 percent significance using Kolmogorov-Smirnov test). Several other statisticaldistributions were also tested but the log-normal distribution was found to be the best-fittingdistribution (Wong & Goh, 2001). The log-normal distribution was also found to be a good fittingmodel in previous studies, the results of which are presented in Figure 1 for comparison.

A major advantage of the log-normal model is its ease of use. The model is calculated with astandard normal distribution table and knowledge of the mean, median and standard deviation. Asan additional advantage, elaborate statistical programs are unnecessary for the use of this model.

It is pertinent to observe that, as compared to previous studies, the present study yielded values thatare consistent with the normative design value of 1 second (typically assumed to satisfy 85 percentof the driving population). Different percentile values can be readily estimated using the log-normaldistribution. As such, it thus becomes possible to incorporate the probabilistic distribution of PRTinto traffic simulations at traffic junctions. With increasing affluence and ageing populations,citizens in developed countries will demand safer roads. As such, design procedures may requiremore rigorous assessment and knowledge of the PRT distribution.


Concluding remarksThe findings reported here are part of ongoing research work into driver behaviour at signalisedjunctions. Other aspects being investigated include the characteristics of driver perception-brakingresponse latency and deceleration profiles, the red-running phenomenon, and junction crashes.

References

[1] Chang, M.S., Messer, C.J. and Santiago, A.J. “ Timing Traffic Signal Change IntervalsBased on Driver Behaviour”, Transportation Research Record 1027, TransportationResearch Board, Washington,. D.C., 1985. pp. 20-30.

[2] Gazis, D, Herman, R. and Maradudin, A. “The problem of the amber signal in traffic flow”,Traffic Engineering, July 1960, pp. 19-26 & 55.

[3] Goh, P.K. and Wong, Y.D. “Driver Stopping Response Latency at Signalised Junctions”,Civil Engineering Research No. 13, School of Civil & Structural Engineering, NanyangTechnological University, January 2000, pp. 40-41.

[4] ITE. “Determining Vehicle Signal Change and Clearance Intervals. ITE”, Technical CouncilTask Force 4TF-1, Institute of Transportation Engineers, Washington, D.C., 1994.

[5] Wong, Y.D. and Goh, P.K. “Perception-Braking Response Time of Unalerted Drivers atSignalized Intersections”, ITE Journal on the Web, Institute of Transportation Engineers,Washington, D.C., Spring 2001.


0

20

40

60

80

100

0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50

Gazis et al. (1960)

Chang et al. (1985)

NTU model (X-jtn)

NTU model (T-jtn)

NTU observed (X-jtn)

NTU observed (T-jtn)

Figure 1. Cumulative percentage of perception-response time (PRT) at signalised junctions

PRT (s)

Cum

ulat

ive

perc

enta

ge (

%)

Spatial Analysis and Modelling of Transport Demand

S H Lam ([email protected])C F Song

IntroductionSpatial distribution of transport demand is an important area in demand analysis, as the modelling of travel isintrinsically spatial. Yet it is also an area that receives rather limited attention especially in the urban activityand travel analysis fields. The relationship between geographic locations and people’s trip making behaviourare often not well described. There is also a lack of knowledge about how geographic characteristics affect theroute and mode decisions of travellers. With the rapid popularisation of GIS technologies, more and moreresearch and professional agencies are starting to adopt spatial analysis as a new way of exploring geographiccharacteristics in demand. However, most of these applications remain at the stage of data assembly andpresentation of model results. The analysis is largely unchanged and does not elaborate on the added capabilityin performing analysis in a spatial manner. In this paper, a GIS-based model for transport demand analysis willbe presented. The model consists of two major components: (i) demand analysis and (ii) demand modelling,making use of the spatial characteristics of travel data. The analysis is based on the data obtained from the 1997Home Interview Survey (HIS) conducted by the Land Transport Authority (LTA), which yielded a richdatabase containing information about travel behaviour in Singapore. A unique feature of the informationcaptured was the geographic locations of the trip records, which allow the identification of both the temporaland spatial movements of different samples at different times.

Data Integration and Geo-codingData from various data sources were first integrated with the travel data to formulate an integrated databasecontaining spatial, socio-economic and travel information. The whole of Singapore island is partitioned into 55zones by following the demarcation set out by the Urban Redevelopment Authority (URA) in its Master Plandefinitions. Land use and socio-economic information was captured from published data obtained from variousauthorities in Singapore. The HIS travel information contains trip records with both trip ends defined by streetnames, buildings, or unique six-digit postal codes. These trip ends were geo-coded making use of the ArcViewand the postal code database. The geo-coding of trip end data covered almost 90% of a total of 44,376 weekdaytrips captured in the 1997 HIS. The loss of some trip information was due to errors in capturing the addressinformation during the survey. The geo-coded trip information was subsequently mapped to the master planzoning scheme. Figure 1 displays the distribution of households in each of the eighty zones.

Figure 1. Distribution of households in zones

Spatial Analysis and ModellingThe analysis of data focuses on the spatial distribution of some of the key survey results. These includehousehold, personal and trip characteristics. The GIS platform provides a convenient way to display theseresults in a map-based environment. As shown in Figure 2, the trips made by the households within JurongWest town were plotted.

Figure 2. Trips made by the Jurong West Town households

The spatial characteristics are modelled statistically. One of the statistical models developed is the relationshipbetween the travel space with factors such as land use, socio-economic and transport characteristics of differenthouseholds. For simplicity, the travel space is represented by straight-line distances travelled (in km) byindividuals. The average travel space (in km) distributions of the eight major trip purposes can beconceptualised into radian graphs. The travel spaces in Jurong West were compared to those in Tampines andthere were notable differences as can be seen in Figure 3. Of the eight purposes shown, travel spaces for workwere the longest and did not differ much between the two towns, whereas in Jurong West, residents tend totravel longer for recreation and shopping than those living in Tampines. This could be due to the presence of aregional centre at Tampines, which can satisfy most of these demands. Further work will be carried out to relatethese patterns to external factors, which will help to explain how these factors affect the space travelled bydifferent individuals for different trip purposes. The results will be useful for planning of locations for variousfacilities in an urban area.

Figure 3. Travel spaces in Jurong West and Tampines

ConclusionsThe use of GIS facilitates a convenient way to perform advanced analysis of transport demand, especially inexploring its spatial nature and developing models that can enhance the state of transport demand modelling.The preliminary results presented in this paper also indicated the significance of geographic characteristics ontransport demand.


WATER

Dispersion of a Turbulent Circular WallJet

Adrian Wing-Keung Law ([email protected])Herlina ([email protected])

IntroductionOne of the simplest configurations for effluent disposalis a direct release through a submerged circular pipe.The pipe is usually secured near the bottom for ease ofconstruction. Initial mixing of the discharges is henceconstrained by the presence of the bottom boundary.Despite being practiced in many industrial projects,there has been little information on the near-fielddispersion characteristics in the literature. The lack ofinformation is partly due to the difficulties inconducting velocity and concentration measurementsvery close to a surface, where traditional intrusivemethods may alter the flow fields and are thus highlyundesirable. In this project, using non-intrusive laserimaging techniques, we quantify experimentally themixing properties of a wall jet where the density of thedischarges is the same as the receiving ambient. Aschematic diagram of the configuration is shown inFigure 1.

zm

zm/2

Um

ym/2

xy

z

Figure 1. Average velocity structure of a three-dimensional wall jet

Experimental ProceduresThe experiments were performed in a glass tank withdimensions of 3 m length, 1 m width, and 1 m depth.A false sloping bottom made from perspex of 1.20 mlength and 0.86 m width was submerged inside thetank and supported by a stainless steel framework. Analuminium orifice with a diameter of 5.5 mm throughwhich the discharge fluid entered the test tank wasplaced on top of the submerged floor. The jet wascontinuously injected into the test tank at a constantflow rate using a peristaltic pump.

Measurements were taken with the laser imagingtechniques of combining Digital Particle ImageVelocimetry and Planar Laser Induced Fluorescent

detailed in [1]. The flow field was illuminated by alaser light sheet produced by a dual-cavity miniNd:Yag laser with an energy level of 25 mJ per pulse.The wavelength of the laser light was 532 nm. Apicture of the illuminated instantaneous flow field isshown in Figure 2 with the laser light sheet projectingfrom underneath.

Figure 2. Flow field under laser light illumination

Polyamid particles with a nominal diameter of 50µmwere introduced into the flow as tracer. The laser lightwas emitted in pulse-pairs to generate a stroboscopiceffect that captures the movement of the particles. Asynchronised CCD camera with a resolution of 1008 x1018 pixel2 then captured the illuminated flow field.For the concentrations, a dissolvable fluorescent dyewas added to the discharge as tracer. Whenilluminated by the pulsing laser light sheets, the dyetracer emits fluorescent light at a wavelength of 590nm (orange). The fluorescence intensity is a function ofboth the dye concentration and the intensity of theincident light. Therefore, if the incident light intensityremains constant, the concentration distribution in theflow field can be determined by noting the variation ofgreyscales in the fluorescence images captured byanother CCD camera.

ResultsQuantitative relationships were obtained for thevariation of the velocities and concentrations for theentire structure of the wall jet. The relationships arelisted in Table 1. Agreement between the equationsand the experimental data is satisfactory.

ConclusionsA detailed experimental study was conducted toinvestigate the dispersion characteristics of a three-dimensional turbulent wall jet. The study yieldsquantitative relationships that satisfy both the massconservation and momentum balance. More resultscan be found in [2].


Table 1 Quantitative relationships

Velocity Concentration

Stream-wise

−

=

2/m

71

2/mmo

m

z

z68.0erf

1

z

z48.1

U

U2

2/cmmo

m

z 21.1

zexp

C

C

−=

Span-wise 1

y

y965.0

1

U

U2

2/m

m+

=

1y

y965.0

1

C

C2

2/m

m+

=

Decay066.1

o

mo

d

x23.9

U

U−

=

1

o

mo

d

x97.6

C

C−

=

Half-height

60.0042.02/ +=d

x

d

zm 31.0061.02/ +=d

x

d

zcm

Half-width

91.121.02/ −=d

x

d

ym 331.02/ −=d

x

d

ycm

References[1] Law, A.W.K. and Wang, H.W. (2000).

“Measurements of mixing processes usingcombined DPIV and PLIF.” Journal ofExperimental Thermal and Fluid Science, Vol.22(3-4), pp213-229.

[2] Law, A.W.K. and Herlina (2000). “Anexperimental study on turbulent circular walljets.” To appear in ASCE Journal of HydraulicEngineering.


Prediction of Transition in Oscillatory Boundary Layers by k-ε Model

Ahmad Sana ([email protected])Shuy Eng Ban ([email protected])

Introduction

The coastal bottom boundary layers undergo transition from laminar to turbulent or vice versain response to changing field conditions. Due to the importance of transitional characteristics ofbottom boundary layer in relation to the sediment movement, a lot of research has been done inthe past. Although many experimental and analytical studies have been carried out, the idea ofusing turbulence models to tackle this phenomenon is relatively new. With the availability ofexcellent computing facilities at affordable costs, this option is gaining more popularity amongthe hydraulic and coastal engineers. The benefit of using a good turbulence model is that itproduces detailed boundary layer properties to facilitate precise estimation of sedimentmovement under a variety of hydraulic conditions. For a turbulence model to be good, anessential requirement is computational economy with reasonable accuracy. With the largenumber of turbulence models available, it is very difficult for practising engineers to choose themost suitable one. The present study deals with the application of a low Reynolds number k-εmodel to a transitional oscillatory boundary layer. The term low Reynolds number implies thatthis model is applicable over the whole cross-stream dimension including the low Reynoldsnumber region (viscous sublayer).

k-ε model and oscillatory boundary layers

The k-ε model was originally developed by Jones and Launder(1972) for steady flowphenomena. Later it was applied to a number of turbulent boundary layers including theoscillatory ones and a number of modifications were proposed to improve its efficiency. Patel etal. (1985) reviewed some of the versions of two-equation models in relation to steady flowphenomena. Tanaka and Sana(1994) reviewed some of the older versions with reference tooscillatory boundary layer properties by using the available experimental data. As a result ofthis study it was found that the original model by Jones and Launder(1972)(JL Model)performed better than the rest of models tested, especially considering the transitional propertiesof oscillatory boundary layers. A similar conclusion has been obtained by Sana andTanaka(2000) after reviewing the original and four newer versions with reference to theavailable Direct Numerical Simulation (DNS) data for oscillatory boundary layers. Anotherinteresting result of this study concerns the nature of damping functions used in Low Reynoldsnumber k-ε models. The damping function used in many of the newer versions involves the wallco-ordinates y+ (=yuf/ν, y = cross-stream distance, uf = shear velocity and ν = kinematicviscosity). In case of oscillatory flow the bottom shear stress goes to zero twice in a wave cycleand at that time the damping function becomes zero in the whole of the cross-stream dimension,which is physically incorrect.

Methodology

In the present study, two of the available versions of k-ε model that meet the requirements ofdamping function outlined by Sana and Tanaka(2000) have been tested against the DNS data bySpalart and Baldwin(1989) for sinusoidal oscillatory boundary layer on a smooth boundary. Thedetails of the governing equations and numerical procedure are provided in Sana and


Tanaka(2000). Here the k-ε models proposed by Yang and Shih(1993)(YS Model) and Abe etal.(1994)(AKN Model) have been tested. The detail about these models is excluded for the sakeof brevity.

Results and discussion

The velocity profile in oscillatory boundary layers shows a distinct overshooting which isefficiently predicted by the models tested here as shown in Figure 1. The cross-stream co-ordinate is normalized by the Stokes length δ l. The YS and AKN models show betterperformance in predicting the velocity profile than that of the JL model from ωt=0o (t = time) toωt=120o, i.e. during acceleration phase and early part of deceleration. At ωt=150o all the threemodels show deviation from the DNS data, which shows the poor performance of these modelsunder deceleration.The comparison of turbulent kinetic energy k (normalized by maximum free-stream velocityUo) profiles is presented in Figure 2. At ωt=30o and ωt=180o, the YS model clearlydemonstrates its supremacy over the other two models by reproducing the k profile especiallynear the wall. During deceleration (ωt=150o) none of the models can predict the cross-streampeak k value, the AKN model performs better far from the wall, though. An interesting featureof the transitional oscillatory boundary layers, i.e. a sudden increase in wall shear stress (τo) indeceleration (ωt=150o) has been very well predicted by the JL model and to some extent by theYS and AKN models as may be observed in Figure 3. The wall shear stress is normalized bymass density ρ and maximum free-stream velocity Uo.

Figure 1. Comparison of velocity profile between JL, YS, AKN model and DNS data


Figure 2. Turbulent kinetic energy profiles

Figure 3. Wall shear stress, free-stream velocity and acceleration

The magnitude of the maximum wall shear stress predicted by the YS and AKN models iscloser to the DNS value than than that by the JL model. It can be observed that this sudden


increase in shear stress occurs at the inflection point in the temporal variation of acceleration(d(U/Uo)/d(ωt)).

Conclusions

The newer versions of k-ε model perform better than the JL model as far as near wall velocitiesand turbulent kinetic energy are concerned. During deceleration (ωt=150o) none of the testedmodels could predict the velocity as well as turbulent kinetic energy precisely. Furtherinvestigation on the predictive ability of these models has to be carried out in order to proposethe possible improvement for better prediction during deceleration.

References

[1] Abe, K., Kondoh, T. and Nagano, Y., 1994, Int. J. Heat Mass Trans., 37, No.1.[2] Jones, W.P. and Launder, B.E., 1972, Int. J. Heat Mass Trans., 15.[3] Patel, V.C., Rodi, W. and Scheuerer, G., 1985, AIAA J. 23, No.9.[4] Sana, A. and Tanaka, 2000, J. Hyd. Engg., ASCE, 126, No.9.[5] Spalart, P. R. and Baldwin, B. S., 1989, Turbulent Shear Flows 6.[6] Tanaka, H. and Sana, A., 1994, Sediment Transport Mechanisms In Coastal Env. And

Rivers.[7] Yang, Z. and Shih, T. H., 1993, AIAA J., 31, No.7.


Turbulence Characteristics of Flow over an Abrupt Change in Bed Roughness Yee-Meng Chiew ([email protected]) Xingwei Chen ([email protected])

IntroductionAn abrupt change in bed roughness in open channel flow is common in hydraulicengineering. A typical example of such an occurrence is the placement of large riprap stoneson a river bed to prevent excessive erosion. Many of the previous studies of thisphenomenon were conducted in close-circuit wind or water tunnels. Of particularsignificance in these experiments was the detection of an overshooting property of the bedshear stress. This describes an abrupt increase of the bed shear stress just downstream fromthe step change (from smooth to rough) in roughness, and which decreases monotonously inthe streamwise direction before slowly returning to its equilibrium value. Fredsoe et al.(1993) reported that the maximum augmented bed shear stress could be as high as about 2.5times its asymptotic value.

The response of velocity and turbulence to a step change in bed roughness in open-channelflow has been investigated experimentally by Nesu and Tominaga (1994). They also reportedthe overshooting property when the flow Froude number = 0.4. However, close examinationsof their data show that the overshooting behavior was only apparent from their resultscalculated using the k-ε model. Their measured data do not support this behaviorunequivocally. This is especially so when one examines their measured data plotted with y/has a function of vu ′′− /Umax

2, where h = flow depth, Umax = maximum flow velocity. In fact,the study of Nesu and Tominaga did not clearly show how the bed shear stress would respondto an abrupt change of bed roughness from smooth to rough in open-channel flow. To thisend, this study aimed to investigate experimentally the response of the bed shear stress to anabrupt change in roughness in open channel flow through the measurements of velocity andturbulence using an acoustic Doppler velocimeter (ADV).

Experimental setupThe rough bed section was simulated by gluing a layer of uniform marble with a diameter =1.12 cm on the flume. The width of the roughened section is the same as the flume (= 0.7 m),and its length is 2 m. The leading edge of the rough bed section is located at a distance 16 mfrom the upstream end of the flume. The beds on both the upstream and downstream end ofthe marble layer section were also roughened with uniform sediment particles with a mediangrain size, d50 = 0.1 cm. Accordingly, the mean bed roughness height, k, is 1.12 cm and 0.1cm for the marble and the sand bed, respectively. Figure 1 shows the schematic layout of theexperimental setup. The two-dimensional instantaneous velocities were measured using anADV system. The mean and turbulent properties of the flows were analyzed.

yx Marble

h

200 cm


Figure 1. Test flume with sudden change of bed roughness

Results and discussionThe flow in the experiment is fully turbulent and the Froude number is 0.43. The water depthis 15.2 cm. Figure 2 shows the distributions of the Reynolds shear stress, represented by

vu ′′− , over the sand and marble bed. Each of the Reynolds shear stress distributions wasmeasured at different x-location along the flume, with x = 0 occurring at the section wherethe bed roughness changes abruptly from smooth to rough. A positive x-value refers to asection downstream of the x = 0 section and vice-versa. The experimental data show that thedistribution of the Reynolds shear stress at x = 10 cm does not change significantly comparedwith that at x = -3 cm, although the roughness has changed abruptly at x = 0. The data at x =10 cm appear to display a memory effect of the upstream flow condition. The response to thechange of roughness is, however, obvious at x = 30 cm where the Reynolds shear stress nearthe bed increases quickly as shown in Figure 2(a). Figure 2(b) illustrates that the near bedReynolds shear stress has reached its equilibrium value (≈ 13 cm2/s2) after 90 cm from theleading edge of marble bed. However, the shear stress distribution is still changing and isapproximately in equilibrium at about x = 180 cm where a linear distribution is observed.

(a) (b) Figure 2. Distributions of Reynolds shear stress along the bed

As we know, the total shear stress distribution, τ(y), in a two-dimensional uniform flow is

dydu

vu µρτ +′′−= (1)

and dydu

µ can be neglected for fully turbulent flow. Extending the Reynolds shear stress

distributions to the boundary, the values of vu ′′− at the bed can be evaluated. The

-u'v' (cm2/s2)0 2 4 6 8 10

y (c

m)

0

2

4

6

8

10

12

14

16

x=30 cmx=10 cmx=-3 cm

-u'v' (cm2/s2)0 2 4 6 8 10 12 14 16

y (c

m)

0

2

4

6

8

10

12

14

16

x=90 cmx=140 cmx=180 cmFull developed


experimental data expectedly show that the value of the bed vu ′′− is larger on the marblebed than that on the sand bed. The increase is gradual, extending from a value of about 7.4cm2/s2 in the sand bed over a transitional regime, reaching an asymptote value to 14.3 cm2/s2

on the marble bed. The distance from the leading edge of the marble bed to where the shearstress is at its asymptotic value is approximately 90 cm although the bed roughness changesabruptly. The shear velocity, *u , can be calculated using:

*u =00 =

′′−=y

vuρτ (2)

where 0τ is bed shear stress. When *u is normalized by its average value on the sand bed,

ou∗ , the streamwise variation of ouu ∗∗ is plotted in Figure 3 as a solid line. As expected, thevalue of ouu ∗∗ changes gradually from unity to its equilibrium value of approximately 1.42over a transitional regime of about 90 cm. The variation of the shear velocity can also beevaluated by fitting the measured of velocity profile to the logarithmic law in a fully roughcondition:

Aky

uu

s

+= ln5.2*

(3)

where u = time average velocity at a vertical distance y from the boundary; sk = equivalent

roughness height, and is assumed = 50d ; and A = integration constant. The fitted results of

*u are superimposed in Figure 3. The measured and computed data compare reasonablywell. Similar to its counterpart of the measured distribution, the computed results also showthat the bed shear stress changes gradually in the transitional regime.

Figure 3. Distributions of shear velocity along the abrupt changed roughness bed

x (cm)-60 -40 -20 0 20 40 60 80 100 120 140

u */u*o

0.5

1.0

1.5

2.0

2.5

By -u'v'By Log-Law


ConclusionsThis study shows the Reynolds shear stress characteristic in open channel flow with an abruptchange in bed roughness from smooth to rough. The response of the Reynolds shear stressdistribution to the sudden change in roughness occurs over the transitional lengths along thebed. Over this transitional length, the bed shear stress changes gradually from its small valueon the upstream smooth bed to the equilibrium value on the rough bed. The result is differentfrom that measured previously in close-conduit flow where an overshoot property of the bedshear stress has been reported. The present study shows that it takes a longer transitionallength for the Reynolds shear stress distribution to reach its equilibrium state.


Alluvial Bed Resistance and Mean Flow Velocity in Flumes and Natural ChannelsGuoliang Yu ([email protected])

Siow-Yong Lim ([email protected])

Introduction

An accurate method to predict the bed formroughness is crucial in determining the overallflow resistance and the mean flow parametersin alluvial channels with bed forms. Since thefirst rational approach by Einstein andBarbarrosa (1952), many other approacheshave been proposed over the last few decadesto predict the bed resistance on alluvial bed.However, many are either not user-friendlyfor computer, or are not adaptable totransition and upper flow regimes. White et al(1981) made comparisons of many of thepredictive equations. They concluded thatamongst the calculated bed friction valueswhich lie within a factor of 2 of the measuredvalues, their equation scored the highest(89%); Einstein and Barbarossa (1952), 21%;Engelund (1966), 83%; and Raudkivi (1967),73%. For the ±25% error band, the score ismuch lower, i.e., White et al (48%), Engelund(38%); and Raudkivi (25%). Brownlie (1981)has compiled by far one of the mostcomprehensive documentation of existingflume and field data in this area. He evaluatedsix methods for predicting friction factor(Brownlie, 1983) and found that nonecompletely satisfied his criteria. Based ondimensional analysis, he then proposed anempirical method to predict the flow depth forthe lower and the upper regime flows. Wu andWang’s (1999) method includes a roughnessparameter A in the non-dimensional shearstress and the flow Froude number. They used494 flume and 450 field data, out of which90% of the flume and 87% of the field dataagree within the ±20% error band when theirequation is used to predict the water depth. Inthis paper, we have indirectly formulated anequivalent bed form roughness without usingthe bed form dimensions. This has led to thedevelopment of a more accurate bedresistance formula to predict the mean flowvelocity in flumes and natural channels.

Alluvial bed resistance and mean flowvelocity

The bed resistance in a two dimensionalalluvial channel with a large aspect ratio maybe divided into the skin resistance related tothe sediment grains on the bed and the formresistance related to the bed forms. Based on aregression of 468 flume data covering a widerange of flow and sediment characteristics, anequation to compute the equivalent bed formroughness size, ksf, has been proposed asfollows:

06.0

50

gb

4

g

b15.0g

50

sf

d

RR

RR

3dk −

σξ= − (1)

where d50= sand size of which 50% is finer,σg= geometric gradation of sediment mixture,Rb= hydraulic radius related to the bed afterthe Einstein sidewall correction, Rg=hydraulic radius due to the grain which can bewritten as

2/3

2/10

′= U

Sn

Rg (2)

where n′ is the Manning roughness coefficientdue to the grain, being assumed to be

196/150dn =′ in the present study (Chien and

Wan, 1999), and S0 is the hydraulic energyslope. The coefficient ξ is 1 if Rg < Rb,otherwise ξ = 0.25. The sign denotes

absolute value for50dRR gb −

. In equation (1), σg

has a negative effect on ksf, which is logicalbecause the coarser particles in a sedimentmixture tend to stablise the bed, and wouldreduce the bed form size accordingly.

Using this modified ks, a new predictiveformula for the mean flow velocity in alluvialchannels is proposed as follows:

−

ξσ+σ

κ=

−

06.0

50

gb4

g

b15.0g

2g

50

b

0b

d

RR

RR

3

dR

27.12ln

SgRU (3)

where U = mean flow velocity, S0= energyslope, g = gravitational acceleration, κ = vonKarman constant, 0.41, the grain roughnesssize is assumed equal to σg

2d50 to take intoconsideration the non-uniformity of the bedmixture.

Application in flumes and natural channels

The data in Figure 1 have been used todevelop Equation (1). A back calculation wasdone to provide a first check on the validity ofEquation (3). Further confirmation of theapplicability of Equation (3) was conducted

using independent flume database of 2857sets and 786 field data sets from differentrivers. Figures 1 and 2 show typical resultsbetween the measured and predictedvelocities. The comparison showed that97.5% of the 4111 sets of data tested werewithin the ±20% error bands. This accuracy inprediction, and the fact that it is achieved for97.5% of the large database used testifies tothe generality and reliability of the formulasin predicting the bed resistance and meanflow velocity in alluvial channels for all flowregimes. The agreement for the field data isparticularly encouraging.

References:

[1] Wu, W. and Wang Sam S.Y. (1999).“Movable bed roughness in alluvialrivers.” J. of Hydr. Engrg., ASCE,125(12), 1309-1312.

[2] Brownlie, W.R. (1983). “Flow depthin sand-bed channels.” J. of Hydr.Engrg., ASCE, 109(7),959-990.

Figure 1. Flume data Group 1: Comparisons between predicted and experiment velocities

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.5 1.0 1.5 2.0 2.5

Measured mean velocity, (m/s)

Cal

cula

ted

mea

n ve

loci

ty,

(m/s

)

Vanoni & Brooks, 1957 Stein, 1965

West Bengal, 1965 Soni, 1980

Willis, 1979 Sato, et al, 1976

Nordin, 1976 Foley, 1975

Costello, 1974 Willis et al, 1972

Onishi et al, 1972 Taylor, 1971

Davies, 1971 Pratt, 1971

Line of perfect agreement

+20%

-20%

Figure 2. Field data: Comparisons between predicted and measured

velocities

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Measured mean velocity, (m/s)

Cal

cula

ted

mea

n ve

loci

ty, (

m/s

)

Yellow River and its canals

Sacramento River

Red River

Colorado River

Missouri River

Snake Clearwater

Portugal River

Niobrara River data

Mountain Creek

Middle Loup River

ACOP Canal

Line of perfect agreement

+20%

-20%


Feasibility of Utilising Reclaimed Lands in Singapore asGroundwater SourceMzila N ([email protected])Shuy E B ([email protected])

IntroductionWhen the current phases of the land reclamation works at Changi are completed, theywill yield a reclaimed land area of about 25 million m2. The land is being reclaimed byfilling up the original seabed with a fairly homogeneous layer of granular material todepths ranging from 6 to 15 m. Figures 1 and 2 show a schematic plan and arepresentative geologic section of the reclaimed area. The reclamation is being carriedout in four phases; Phases 1A and 1B were completed in 1994, Phase 1C wascompleted in 1997, while the latest phase called area A is still in progress. The filledmaterial forming the upper stratum consists mainly of coarse sand, and is boundedbelow by the original soft clay seabed with traces of seashell fragments. The upper‘unconfined aquifer’ is characterised by high porosity values of over 35 %, and ahydraulic conductivity of about 60 m per day. This study looks into the feasibility ofdeveloping the reclaimed land as a potential groundwater source.

Figure 1. Schematic layout of reclaimed area

ws-137 ws-128 ws-112 ws-107


Figure 2. A representative geologic section of the reclaimed land (cross section throughdotted line in Figure 1)

Salinity distribution of existing groundwaterThe reclaimed land sits on an original open seabed. When first completed, thegroundwater in it was saline. Over a period of sustained natural rainwater recharge, theoriginal seawater has gradually been replaced by fresh rainwater. To assess the extentto which the saline water has been displaced by freshwater, field measurements of thegroundwater salinity were carried out at 50 standpipes that had been installed at the sitefor groundwater level monitoring. The field salinity surveys were conducted over theperiod from October 1999 to March 2000. The YSI Model 33 Salinity-Conductivity-Temperature (S-C-T) Meter was used for salinity measurement. Figures 3 to 6 show themeasured salinity profiles at four selected stand pipes. The results show that the uppergroundwater layer is very fresh, with salinity values of below 1000 mg/l, or 1 ppt, todepths of 4 to 10 m below the water table. Thereafter, the salinity typically increasesfrom 1000 mg/l to 4000 mg/l over the next 2-m increase in depth. This indicates a well-defined interface between fresh and saline water layers within the groundwater body.


Groundwater 24/1/2000 (Ws 112)

-101234567

0 1 2 3 4 5 6Salinity ppt

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Groundwater qualityA groundwater sample was collected from standpipe a4s-17 for quality analyses in thelaboratory. The results were compared with the constituent concentrations before andafter reverse osmosis at Water Factory 21, Orange County (National Research Council,USA, 1994) in Table 1. The results show that the concentrations of Chloride, Nitrate,and Total Dissolved Solids are below those obtained after Reverse Osmosis, while theSulphate concentration was higher at the study area. A more extensive field samplingand laboratory analysis programme is in progress for a more comprehensive qualitycharacterisation of the groundwater.

Table 1. A comparison of quality parameters of groundwater at Changi and that ofWater Factory 21.

Constituent Units Changi A4s-17

Water Factory 21before Reverse Osmosis

Water Factory 21 afterReverse Osmosis

TDS mg/l -- 1230 72Sodium Mg/l 1.89 270 24Iron Mg/l 0.04 0.04 0.04Magnesium Mg/l 38.2 4.3 0.1Zinc Mg/l 0.39 0.05 0.05Copper Mg/l 0.03 0.0013 0.001Mercury ppb 0.4 0.5 0.5Lead Ppb ND 1 1Manganese Mg/l 0.17 0.02 0.0015Chloride Mg/l 31.46 373 40

Feasibility of the reclaimed land as a groundwater sourceThe reclamation works being carried out at Changi have unintentionally created asubstantial highly permeable, unconfined coastal aquifer which could potentially bedeveloped as a groundwater source. Based on the groundwater table records in January2000 and the results of field salinity surveys, there are about 8.9x106 m3 of aquifervolume with groundwater salinity of less than 1000 mg/l, 5.2x106 m3 of aquifer withsalinity of between 1000 mg/l and 2000mg/l and 3.4x106 m3 of aquifer with salinityvalues between 2000mg/l and 4000mg/l. Groundwater with salinity of 1000mg/l isdefined as weakly fresh and treatable for potable use (Bolle I., Lebbe L.C., and De


Breuck W. 1990). The ground porosity was computed from density readings measuredat 89 different bed locations distributed throughout the study area. Effective porosityover the whole area ranges from 35 percent to 50 percent, which are typical values forcoarse sand. Assuming an average porosity of 35 percent, the total volume of ‘usable’groundwater in storage is estimated at 18.9 million m3. The high porosity andpermeability of the ground allows practically all the natural rainfall over the surface,which averages about 2.4 m each year, to be readily infiltrated. In the longer term, acentralised wastewater treatment plant has been planned at the reclaimed site. Thiscould provide a steady source of treated wastewater for recharging the groundwater.The potential sustainable yield from this man-made aquifer, taking into account thecombined natural rainwater and potential artificial recharge, could be economicallyviable. The water recharge and extraction scheme could face two major challenges. Thefirst is the risk of long term salt-water intrusion caused by excessive deep wellpumping. Groundwater abstraction from coastal aquifers has been practised in manyparts of the world for a long time, and there are established techniques for controllingthe salt-water intrusion. Hence technical solutions exist today which could effectivelycounter the problem of salt water intrusion. The second problem is the quality of theextracted groundwater. The quality can be maintained by controlling the quality of therecharge water, and hence the standard of treatment at the wastewater treatment plant,and by optimising the travel distance and resident time of the recharge water in theground. Further studies are being carried out to assess the viability of developing thereclaimed land as a groundwater source.

References[1] Bolle I. Lebbe L.C., and De Breuck W.,(1991) A mathematical model of the

evolution of the fresh-water lens under dunes and beach with semi-diurnal tides.Hydrogeology of Salt Water Intrusion, a selection of SWIM Papers. Vol. 11147-163. IAH.

[2] National Research Council (U.S.) Committee on Ground Water Recharge.Ground ater recharge using waters of impaired quality, Washington, D.C.:National Academy Press, 1994 pp 283.

Acknowledgement:The generous cooperation and assistance of SPECS Consultants Pte Ltd in providingessential data and information needed for this study is gratefully acknowledged


Effect of Urbanisation Sequence on Flood Peak Increase of an Overland PlaneTommy S. W. Wong ([email protected])

While many studies have shown that urbanisation causes flood peaks to increase, acomparison of their results shows that the differences are large. One reason may bedue to different locations of urbanisation within a basin. However, to assess theinfluence of location or sequence of urbanisation on the flood peak is no easy task.First, it is impractical to carry out an experimental study. Even on a small basin, theconstruction, maintenance, and demolition costs of such a study will be prohibitivelyhigh, the duration will be extremely long, and then the urbanisation patterns will belimited. Second, if the study is carried out by means of observed flood data, in orderto obtain various degrees of urbanisation, it will be necessary to combine data fromseveral basins. Since the physical characteristics of drainage basins are mostlyheterogeneous, and the hydrometeorological characteristics of causative storms aremostly different, to combine the flood data from these basins will require muchsubjective interpretation. Indeed, due to all these practical difficulties, the issue hasnever been resolved.

On the other hand, by applying a physics-based method such as the kinematic wavemethod to an idealised situation such as the overland plane, it is feasible to carry out atheoretical study. Analytical solutions for the given situation could be obtained, inwhich the influence of each individual parameter such as the Manning resistancecoefficient, n, or the runoff coefficient, C, on the flood peak can be clearly revealed.

In this study, by considering urbanisation on an overland plane as a process whereby arelatively rough, permeable surface is gradually replaced by a relatively smooth,impermeable surface, the effect of urbanisation sequence on the flood peak is assessedby the kinematic wave method. In the assessment, two opposing urbanisationsequences are considered: one from downstream to upstream, and the other fromupstream to downstream (Figure 1). Further, the reduction in surface roughness isrepresented by the ni/np ratio, and the reduction in permeability is represented by theCi/Cp ratio. The subscript i denotes the properties that relate to the impermeablesurface, and the subscript p denotes the properties that relate to the permeable surfaceof the plane. The ratios ni/np = 1/10 and Ci/Cp = 10 represent a large reduction insurface roughness and permeability; while the ratios ni/np = 1/2 and Ci/Cp = 2represent a small reduction in surface roughness and permeability. For bothurbanisation sequences and for all degrees of urbanisation, the results (Figure 2) showthat surface conversion from rough to smooth and from permeable to impermeablecauses the flood peak to increase. For a partially-urbanised plane and for the samedegree of urbanisation, urbanisation at the downstream end generally causes greaterincreases in the flood peak. This phenomenon can be attributed to the partial-areaeffect, which means that the flood peak derived from the downstream urbanisedportion of the plane is greater than that derived from the entire plane. In terms ofurbanisation sequence, the downstream to upstream urbanisation sequence generallycauses greater increases in the flood peak. The effect of urbanisation sequence on theflood peak is significant for the larger reductions in surface roughness andpermeability.


Flow

Flow

upstream

upstream

downstream

downstream

Figure 1. Sequence of urbanisation on an overland plane

Figure 2. Flood peak increase on an overlandplane with two opposing urbanisation

0 10 20 30 40 50 60 70 80 90 100

60

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ni/np =1/2 & Ci/Cp = 2

ni/np =1/5 & Ci/Cp = 5

Downstream to Upstream

ni/np =1/10 & Ci/Cp = 10

ni/np =1/5 & Ci/Cp = 5

Upstream to Downstream

ni/np =1/2 & Ci/Cp = 2

ni/np =1/10 & Ci/Cp = 10

CSE Research Bulletin No. 14. January 2001: Research Reports

ISSN 0219-0370 January 2001 NO. 14

Abstracts of all the research reports are available in the form of PDF (portable document file) format. If

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RESEARCH REPORTS

Modelling of Phosphorus Dynamics in Aquatic Sediments with SpecialApplication to a Tropical ReservoirCandidate : Hong WangReport No: CSE/PhD/2000/23Sediment phosphorus models, consisting of six interrelated equations, have beendeveloped to predict the dynamic behaviour of organic, exchangeable particulate anddissolved phosphorus in aquatic sediments. The models concentrate on the active toplayer on the sediment-water interface. This layer is divided into aerobic and anaerobiclayers. The proposed models involve biological and geochemical mechanismsassociated with the phosphorus in sediments. Compared with existing models, theproposed system directly models the dynamics of dissolved and particulatephosphorus incorporating the kinetics and non-linear isotherms of sorption processes.Such an approach will dynamically couple the two forms of phosphorus. Theseimprovements realise the buffer function of sediments in modelling phosphorusdynamics. The models were solved by numerical integration and coded with dynamicsimulation software “Powersim” which makes the models run in the form of flow-charts under MS Windows. Field investigations and laboratory experiments have beenconducted to understand the dynamic characteristics of phosphorus in Kranji reservoirand to estimate the relevant parameters for the model application. The decompositionof organic matter in sediments was investigated to determine its kinetics and fractionsby incubating sediment samples in the laboratory for 7 months. Sorption kinetics andisotherms of phosphorus in sediments, under both aerobic and anaerobic conditions,were experimentally investigated. The quarterly released fluxes of phosphorus fromthe sediments were simulated by incubating undisturbed sediment cores in thelaboratory. The models were validated using the field measurements of ChesapeakeBay US and then applied to Kranji reservoir in Singapore to determine short and long-term predictions of phosphorus dynamics and also to appraise internal loading insediments. As an extension, three rehabilitation techniques, which may be used for in-site treatment to reduce the internal loading of phosphorus, have been evaluated usingthe derived models.

Stability and Strength Of Steel Structures under Thermal EffectsCandidate: Toh Wee SiangReport No: CSE/PhD/2000/24This thesis presents both numerical and analytical methods for the analysis of steelstructures under thermal effects. These methods comprise finite element method(FEM), first- and second-order elastic-plastic hinge methods, and the Rankineapproach. These methods deal with rigid-jointed plane frames subjected to elevatedtemperatures. The classical plastic theorems have been successfully extended toincorporate the thermal effects, with new definitions and mathematical proofs. TheRankine approach allows for the interaction of strength and stability aspects of astructure to determine an approximation of fire resistance of steel members andframes. The strength and stability aspects can be evaluated from the plastic andelastic buckling analyses, respectively. A consistently good agreement with bothnumerical and test results shows that for steel structures under thermal effects, theFEM provides an economical way to investigate the structural behaviour, while theRankine approach provides a quick tool to assess the ultimate fire resistance.


Pile-Soil Interaction In Layered Soil MediaCandidate: Zhou HanbinReport No: CSE/PhD/2000/25A semi-analytical numerical method for pile-soil interaction in layered soil media isproposed in this thesis. The analysis incorporates both the merits of simplicity offinite layer method for soil continuum and the generality and flexibility of finiteelement method for piles and raft. The formulation is versatile and efficient. It isconvenient for developing parametric studies and investigating the influence ofparameter variation on pile foundation response. The numerical evaluations andvalidations for the analysis of single piles, pile-pile interactions, pile groups, rafts andpiled rafts are presented. Special attention is given to the piles and pile groups inlayered and non-homogeneous soils. The non-linear response of piled raft is alsoaddressed. Parametric studies were carried out to identify the influence of variousgoverning factors. The typical parameters of the soils and piles are discussed toenhance the understanding of the pile–soil interaction.

Evaluation of Load Transfer Behaviour of Bored Piles in Residual SoilIncorporating Construction EffectCandidate: Zhu HongReport No: CSE/PhD/2000/26Large diameter bored piles are widely used for the support of heavy loads in areascovered by residual soils. Current practice for the design of bored piles in residualsoils is inadequate due to a lack of understanding of load transfer along the piles andinsufficient consideration of construction effect. In order to improve the design ofbored piles in residual soils, one needs to have a full understanding of the loadtransfer behaviour and to be able to correctly evaluate the load transfer curves fromsite investigation data using a procedure that incorporates the construction effect.In this study, extensive laboratory and in-situ tests were carried out to investigate theconstruction effect such as soaking and placing of fresh concrete on the soil propertiesfor a residual soil formation in Singapore. The shear strength and the deformationalproperties of the residual soil were found to deteriorate with soaking. There was amoisture change in the soil near soil-concrete interface due to interaction between soiland fresh concrete. The moisture change was found to be highly dependent on theliquidity index of the soil and the water/cement ratio. From a parallel study involvingpullout tests on miniature bored piles, the ultimate unit shaft resistance was found tobe reduced by 5-10% when the borehole was soaked for 0.5-2 hours and up to 20%for a longer duration of soaking. Similar orders of reduction were also found in loadtests of full-scale bored piles. A finite element analysis indicated that the soil adjacentto the shaft will undergo distinctive changes in stress states and deformation patternsat different construction stages and that the horizontal stress will not return to itsoriginal state. The minimum horizontal stress was found to occur some distance awayfrom the shaft and the after-construction coefficient of earth pressure K was found tobe dependent on the coefficient of earth pressure at rest K0, the support and theconcrete pressure. An analytical model developed in consideration of the stresshistory of the soil and the stress path encountered was proposed for predicting thestress changes around the shaft during the various stages of construction. Thistheoretical approach provides a useful insight into construction factors that affect thepile performance, and a framework for the development of refined analysis of thebehaviour of bored piles. A procedure that accounts for the nonlinear decrease of


modulus with an increase in strain/stress level and construction effects was developedfor the analysis of the load transfer along a bored pile. Results of the analysis, whencompared with results from load tests on several instrumented bored piles, showedthat the proposed approach is capable of producing load-transfer (t-z) curves and,subsequently, the load-displacement curves for bored piles in residual soils.

Parametric Study of Strengthened Multiplanar Tubular JointsPrincipal Investigator: Fung Tat ChingReport No: CSE/2000/72This report presents the experimental and numerical studies of the ultimate capacitiesof doubler plate reinforced uni-planar T and multi-planar XT tubular joints. Two full-scale test specimens (one T joint and another XT joint) were tested to failure undercompressive in-plane brace load. The finite element results were compared with theexperimental results and good agreements were obtained. The finite elementmodelling techniques were then verified and can be used with confidence. Aparametric study was then carried out based on the test specimens’ dimensions andconfigurations with various brace loading. The contribution of the doubler plate wasfound to be significant. The ultimate capacity and joint stiffness for the reinforcedjoints were much higher than the un-reinforced joints. The influences of the geometricparameters were then investigated. It was found that the brace thickness to chordthickness ratio and the doubler plate length would not have much influence on theultimate capacity. On the other hand, the brace diameter to chord diameter ratio, thechord radius to chord thickness ratio and the axial load in the out-of-plane braces werefound to have strong influence on the ultimate capacity of the doubler plate reinforcedtubular joints.

Behaviour of Soil Nailed Retaining StructuresPrincipal Investigator: Low Bak KongReport No: CSE/2000/73The behaviour of nailed soil walls was studied using model tests and numericalmethods. The influence of nail length, nail inclination, facing stiffness and method ofnail installation on the behaviour of the walls was investigated. Pull-out tests werealso conducted to study the mobilised bond stress at the nail-soil interface. The mainmodel tests were carried out in a concrete-lined and sheltered trench, and involved sixsoil nailed walls each 2.4 m high, 5.0 m long, and 3.0 m wide. The walls had differentnail length, nail inclination and density of sand. The behaviour of the walls and thestrains in the soil nails were monitored both during excavation stages and undersurcharge loading. Numerical modelling using the programs FLAC and ABAQUSshowed reasonable agreement with the measured behaviour of the test walls and soilnails. Program FLAC was subsequently used to study the influence of otherparameters which were not varied in the actual tests. The experimental and numericalstudies indicated only small bending moments in the nails. Axial tension is thepredominant force. The contribution of nail bending stiffness to the stability of thetrench-scale nailed soil walls appears to be small. At failure, the slip surface of thenailed soil is curved and becomes nearly vertical where it meets the horizontal groundsurface.

CSE Research Bulletin No. 14. January 2001: Publications

ISSN 0219-0370 January 2001 NO. 14

The CSE publications list is available in the form of PDF (portable document file) format. If you do not

have PDF, please click to download and install the Acrobat Reader for Windows 95, Windows 3.1, Window-NT, DOS, Macintosh, OS2, LINUX, etc. To view and print the article, run Acrobat Reader and click the link below.

CSE publications list

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Publications of academic staff in journals and conference proceedings during the period from1 July 1999 to 30 June 2000. Authors who are not members of the School are marked by *.

Abella, C.A.,* Ivanov, V.N., Kim, I.S.,* and Doncel, G.F.,* 2000. Labeled trinucleotides asquantitative probes for in situ hybridization to identify Bacillus spp. Molecular and CellularProbes, Vol. 14, pp. 89-93.

Agus, S.S., Leong, E.C. and Rahardjo, H., 1999. Field measurements of permeability for residualsoils. Proceedings of the 5th International Symposium on Field Measurements in Geomechanics,Leung et al. (Eds), A.A. Balkema, Singapore, 1-3 December, pp. 537-542.

Agus, S.S., Leong, E.C. and Rahardjo, H., 2000. A triaxial permeameter for unsaturated soils.Proceedings of the Asian Conference on Unsaturated Soils, Unsaturated Soils for Asia, H.Rahardjo, D.G. Toll and E.C. Leong (Eds), A.A. Balkema, Singapore, 18-19 May, pp. 365-370.

Appan, A. and Hong, W.,* 2000. Sorption isotherms and kinetics of sediment phosphorus in atropical reservoir. Journal of Environmental Engineering, ASCE, Vol. 126, No. 11, pp. 993-998.

Appan, A., 1999. Pollution control and management aspects of water resources development inSingapore. (Invited paper) Presented at Water Management Asia 99 Conference held in Singapore,1-2 December.

Appan, A., 1999. Quenching urban thirst in the next millennium. (Invited paper) Presented at theGlobal Change Conference on “Understanding the Earth System: Compartments, Processes andInteractions”, 24-26 November, Bonn, Germany.

Appan, A., 1999. Trends in water demands and the role of rainwater catchment systems in the nextmillennium. (Keynote address), Proceedings of the 9th International Conference on RainwaterCatchment Systems, Petrolina, Brazil, 6-9 July, pp. 6-10.

Appan, A., 1999. Water pollution control – The Singapore experience. Presented in Seminarsponsored by APCEL, Ministry of Foreign Affairs & World Bank Institute in Allson Hotel,Singapore, 17 November.

Appan, A., 1999. Water supply and sanitation: trends and developments. (Invited paper)Proceedings of the 9th Water Symposium, Stockholm International Water Institute, Stockholm,Sweden, 9-12 August, pp. 341-352.

Aung, K.K.*, Rahardjo, H., Toll, D.G.* and Leong, E.C., 2000. Mineralogy and microfabric ofunsaturated residual soil in “Unsaturated Soils for Asia“, eds.: Rahardjo, H. et al., Proceedings ofthe Asian Conference on Unsaturated Soils (UNSAT-ASIA 2000) – From Theory to Practice,Singapore, 18-19 May, Balkema, pp. 317-321.


Bo, Myint-Win*, Chu, J., and Choa, V.*, 1999. Factors affecting the assessment of degree ofconsolidation. Proceedings of the 5th International Symposium on Field Measurements inGeomechanics, 1-3 December, Singapore, pp. 481-486.

Bo, Myint-Win*, Chu, J., and Choa, V.*, 2000. Discharge capacity of prefabricated vertical drain.Proceedings of the 2nd Asian Geosynthetics Conference, 29-31 May, Kuala Lumpur, Vol. 2, pp.167-172.

Brownjohn, J.M.W. and Xia, P., 1999. Finite element modelling, prototype testing and modelupdating of a curved cable-stayed bridge. Proceedings of the International Conference onApplications of Modal Analysis, Gold Coast, Australia, December, 10 p.

Brownjohn, J.M.W. and Xia, P., 2000. Dynamic assessment of curved cable-stayed bridge bymodel updating. Journal of Structural Engineering, ASCE, February, Vol. 126, No. 2, pp. 252-261.

Brownjohn, J.M.W., 1999. Dynamic performance and characteristics of highway bridges.Proceedings of the International Conference on Current and Future Trends in Bridge Design,Repair and Maintenance, Singapore, October, pp. 551-562.

Brownjohn, J.M.W., 1999. Energy dissipation in one-way slabs with human participation.Proceedings of the Asia Pacific Vibration Conference, Singapore, December, Vol. 1, pp. 155-160.

Brownjohn, J.M.W., Lee, H.J.* and Cheong, K.C.*, 1999. Dynamic performance of a curvedcable-stayed bridge. Engineering Structures, Vol. 21, pp. 1015-1027.

Brownjohn, J.M.W., Pan, T.C. and Deng, X.Y., 2000. Correlating dynamic characteristics fromfield measurements and numerical analysis of a high rise building. Earthquake Engineering andStructural Dynamics, Vol. 29, No. 4, pp. 523-543.

Brownjohn, J.M.W., Pan, T.C. and Deng, X.Y., 2000. Macro-updating of finite element modellingfor core systems of tall buildings. Proceedings of the 14th Engineering Mechanics Conference,ASCE, Austin, Texas, 21-24 May, p. 6.

Cai, J.G. and Zhao, J., 2000. Comparisons between effects of linear and nonlinear deformationalbehaviors of fractures on P-wave attenuation. Proceedings of the 4th North American RockMechanics Symposium, Seattle, USA.

Cai, J.G. and Zhao, J., 2000. Effects of multiple parallel fractures on apparent attenuation ofwaves in rock masses. International Journal of Rock Mechanics and Mining Sciences, Vol. 37, pp.661-682.


Chan, T.K. and Poh, C.K.*, 2000. Behaviour of precast reinforced concrete pile caps.Construction and Building Materials, March, Vol. 14, No. 2, pp. 73-78.

Chan, T.K. and Porter Goff, R.F.D.*, 2000. Welded aluminium alloy connections: a simplifiedplastic model. Proceedings of the Institution of Civil Engineers, Structures & Buildings, May, Vol.140, No. 2, pp. 161-168.

Chan, T.K. and Porter Goff, R.F.D.*, 2000. Welded aluminium alloy connections: test results andBS8118. Thin Walled Structures, April, Vol. 36, No. 4, pp. 265-287.

Chan, T.K., Lim, S.H.*, Tan, H.T.W.* and Lim, C.P.*, 1999. Variation of bending capacity alongthe lamina length of a grass, imperata cylindrica var. major (Gramineae). Annals of Botany,December, Vol. 84, No. 6, pp. 703-708.

Chang, M.F., 1999. Enhancing the value of load tests on preliminary bored piles. Proceedings ofthe Civil and Environmental Conference – New Frontiers and Challenges, Bangkok, November,Vol. 2, pp. V∼29-V∼38.

Chang, M.F., 2000. Basal stability analysis of braced cuts in clay. Journal of Geotechnical andGeoenvironmental Engineering, ASCE, March, Vol. 126, No. 3, pp. 276-279.

Chang, M.F., Teh, C.I. and Cao, L.F., 1999. Critical state parameters of saturated clays frommodified cam clay model. Canadian Geotechnical Journal, Canada, October, Vol. 36, No. 5, pp.876-890.

Chen, C.N., Law, A.W.K. and Sun, W.D., 1999. Measures to mitigate the formation of sandbars atcoastal drainage outlets. ENV-NTU-NUS R&D Symposium, May.

Chen, S.G., Jain, M. and Zhao, J., 2000. A new model of joint shear strength under cyclic loads.Proceedings of the 4th North American Rock Mechanics Symposium, Seattle, USA.

Chen, S.G., Zhao, J. and Zhou, Y.X.,* 2000. 3DEC modelling of a small-scale field explosion test.Proceedings of the 4th North American Rock Mechanics Symposium, Seattle, USA.

Cheng, N.S. and Chiew, Y.M., 1999. Analysis on initiation of sediment suspension. Journal ofHydraulic Engineering, ASCE, Vol. 125, No. 8, pp. 855-861.

Cheng, N.S. and Chiew, Y.M., 1999. Closure to Pick-up probability for sediment entrainment.Journal of Hydraulic Engineering, ASCE, Vol. 125, No. 7, pp. 786-788.


Cheng, N.S. and Chiew, Y.M., 1999. Incipient sediment motion with upward seepage. Journal ofHydraulic Research, IAHR, Vol. 37, No. 5, pp. 665-681.

Cheng, N.S. and Law, A.W.K., 2000. Decay of turbulence generated by oscillating grid.Proceedings of the Symposium on Stochastic Hydraulics, Beijing, China, pp. 167-172.

Cheng, N.S., Law, A.W.K. and Findikakis, A.N.*, 1999. Effect of nearshore currents on oiltransport. Proceedings of the 3rd International Symposium on Ecohydraulics, Utah City, Utah,USA (in CD-ROM).

Cheng, Q.H.*, Lok, T.S. and Xie, Z.C.*, 1999. Geometrically non-linear analysis including sheardeformation of composite laminates. Journal of Thin-Walled Structures, UK, September, Vol. 35,No. 1, pp. 41-59.

Cheong, H.K. and Macalevey, N., 2000. Experimental behaviour of jacketed reinforced concretebeams. Journal of Structural Engineering, ASCE, June, Vol. 126, No. 6, pp. 692-699.

Cheong, H.K., Tay, J.H. and Show, K.Y., 2000. Utilization of municipal solid waste fly ash asinnovative civil engineering materials. Proceedings of the International Symposium - SustainableConstruction: Use of Incinerator Ash, University of Dundee, UK, 20-21 March, pp. 369-380.

Chiew, S.P. and Dai, C.W., 1999. Experimental study of steel I-beam to CFT column connections.Proceedings of the 2nd International Conference on Advances in Steel Structures, Hong Kong, 15-17 December, Vol. I, pp. 291-304.

Chiew, S.P. and Dai, C.W., 1999. Steel I-beam to CFT column multiplanar connections withdifferent stiffening details. Proceedings of the 6th International Conference on Steel and SpaceStructures, Singapore, 1-3 September, pp. 407-414.

Chiew, S.P. and Soh, C.K., 2000. Strain concentrations at intersection regions of a multiplanartubular DX-Joint. Journal of Constructional Steel Research, UK, February, Vol. 53, No. 2, pp.225-244.

Chiew, S.P. and Wu, N.W., 1999. Multiplanar effects in fatigue design of steel tubular XT- andXX-Joints. Proceedings of the 6th International Conference on Steel and Space Structures,Singapore, 1-3 September, pp. 253-262.

Chiew, S.P., Dong, Y.X. and Soh, C.K., 1999. Concrete-steel plate interface characteristics forcomposite construction. Proceedings of the 7th International Conference on Civil and StructuralEngineering Computing – Computing Developments in Civil and Structural Engineering, CIVIL-COMP’99, Oxford, UK, 13-15 September, pp. 35-40.


Chiew, S.P., Dong, Y.X. and Soh, C.K., 1999. Non-linear finite element modeling of concrete-filled steel tube columns. Proceedings of the 7th International Conference on Civil and StructuralEngineering Computing, CIVIL-COMP’99 – Development in Analysis & Design using FiniteElement Methods, Oxford, UK, 13-15 September, pp. 197-204.

Chiew, S.P., Soh C.K. and Wu, N.W., 2000. SCF equations for fatigue design of steel multiplanartubular XX-Joints. Proceedings of the 10th International Offshore and Polar EngineeringConference, ISOPE-2000, Seattle, USA, 28 May – 2 June, Vol. IV, pp. 34-40.

Chiew, S.P., Soh, C.K. and Wu, N.W., 1999. Experimental and numerical stress analyses of atubular XT-joint. Journal of Structural Engineering, ASCE, November, Vol. 125, No. 11, pp. 1239-1248.

Chiew, S.P., Soh, C.K. and Wu, N.W., 1999. SCF equations for the fatigue design of multiplanartubular XT-Joints. Proceedings of the 9th International Offshore and Polar Engineering Conference,ISOPE-99, Brest, France, 30 May – 4 June, Vol. IV, pp. 82-89.

Chiew, S.P., Soh, C.K. and Wu, N.W., 2000. General SCF design equations for steel multiplanartubular XX-Joints. International Journal of Fatigue, UK, April, Vol. 22, No. 2, pp. 283-293.

Chiew, S.P., Soh, C.K., Fung, T.C. and Soh, A.K.*, 1999. Numerical study of multiplanar tubularDX-joints subject to axial loads. Journal of Computers and Structures, UK, July, Vol. 72, No. 6,pp. 749-761.

Chiew, Y.M. and Lim, F.H., 2000. Failure behavior of riprap layer at bridge piers under live-bedconditions. Journal of Hydraulic Engineering, ASCE, Vol. 126, No. 1, pp. 43-55.

Choi, E.C.C. and Hidayat, F., 2000. Turbulence characteristics during thunderstorms - somepreliminary results. APEC Workshop on Alignment of Standards in the Building Industry,Melbourne.

Choi, E.C.C., 1999. Extreme wind characteristics in Singapore. Journal of Wind Engineering andIndustrial Aerodynamics, Netherlands, Vol. 83, pp. 61-69.

Choi, E.C.C., 2000. Wind characteristics of tropical thunderstorms. Journal of Wind Engineeringand Industrial Aerodynamics, Netherlands, Vol. 84, pp. 215-226.

Chow, K.K., Wang, J.Y. and Tay, J.H., 2000. Hydroponic cultivation of leafy vegetables in primaryand secondary municipal wastewater. Proceedings of the World Congress on Soilless Culture on‘Agriculture in the Coming Millennium,’ Israel, 14–18 May.


Chu, J. and Leong, W.K.*, 1999. Discussion on Static liquefaction of very loose sand. CanadianGeotechnical Journal, Vol. 36.

Chu, J., Bo, M.W.*, and Choa, V.*, 1999. Determination of undrained shear strength of clay bydirect simple shear tests. Proceedings of the 11th Asian Regional Conference on Soil Mechanicsand Foundation Engineering, Seoul, 16-20 September, Vol. 1, pp. 49-52.

Chu, J., Leong, W.K.*, Jai, X.L.*, and Lee, C.W.*, 1999. Stability of submarine granular slopes.Proceedings of the 2nd International Conference. on Landslides and Stability and Safety ofInfrastructures, Singapore, 27-28 July, pp. 139-147.

Chuang, P.H. and Kong, F.K.*, 1999. Discussion by A. N. Beal on “Large-scale tests on slenderreinforced concrete columns”. The Structural Engineer, 9 December, Vol. 77, No. 23 & 24.

Chuang, P.H. and Li, X.*, 1999. Non-iterative flexibility method for nonlinear analysis of frames.Journal of Structural Engineering, ASCE, Vol. 125, No. 11, pp. 1338-1346.

Chuang, P.H. and Li, X.*, 1999. Nonlinear frame analysis using flexibility approach withmathematical programming application. USNCCM99 Book of Abstracts, USACM/USNCCM995th US National Congress on Computational Mechanics, University of Colorado, Boulder,Colorado, editors: Alejandro Carosio, Pawel Smolarkiewicz, Kaspar Willam, and Jisung Yang, 4-6August, pp. 488-489.

Chui, P.C., Tay, J.H., Terashima, X.*, Ozaki, H.* and Jeyaseelan, S., 1999. Nitrogen removal insubmerged filter with no recirculation. Proceedings of the 7th IAWQ Asia-Pacific RegionalConference on Water Quality and Pollution Control, Taipei, Taiwan, 18-20 October, Vol. 2, pp.251-256.

Chui, P.C., Terashima, Y.*, Tay, J.H. and Ozaki, H.*, 1999. Simultaneous organics and nitrogenremoval using submerged filters. Proceedings of the Conference on Biofilm Systems, New York,USA, October.

Chui, P.C., Terashima, Y.*, Tay, J.H., Ozaki, H.* and Jeyaseelan, S., 1999. Nitrogen removal in asubmerged filter with no effluent recirculation. Journal of Water Science and Technology, Vol. 42,Nos. 3-4, pp. 51-58.

Cui, S., Cheong, H.K. and Hao, H., 1999. Experimental study of dynamic buckling of plates underfluid-solid slamming. International Journal of Impact Engineering, UK, Vol. 22, pp. 675-691.

Cui, S.J., Cheong, H.K. and Hao, H., 2000. Experimental study of dynamic post-bucklingcharacteristics of columns under fluid-solid slamming. International Journal of EngineeringStructures, Vol. 22, No. 6, pp. 647-656.


Deutscher M.S.*, Gasmo, J.M.*, Rahardjo, H., Leong, E.C. and Tang, S.K.,* 2000. Changes inmagnitude and distribution of pore-water pressures for a typical residual soil slope in Singapore in“Unsaturated Soils for Asia“, eds. Rahardjo, H. et al., Proceedings of the Asian Conference onUnsaturated Soils (UNSAT-ASIA 2000) – From Theory to Practice, Singapore, 18-19 May,Balkema, pp. 777-782.

Eriktius, D.T.*, Leong, E.C. and Rahardjo, H., 2000. Use of municipal solid waste fly ash as anadmixture for peaty soils. Proceedings of the 4th Kansai International Geotechnical Forum(KIGForum 2000), Creation of New Geo-Environment, Kyoto, Japan, 24-26 May, pp. 149-154.

Fung, T.C., 1999. Complex-time-step methods for transient analysis. International Journal forNumerical Methods in Engineering, November, Vol. 46, Issue 8, pp. 1253-1271.

Fung, T.C., 1999. Weighting parameters for unconditionally stable higher-order accurate timestep integration algorithms Part 1. First order equations. International Journal for NumericalMethods in Engineering, July, Vol. 45, No. 8, pp. 941-970.

Fung, T.C., 1999. Weighting parameters for unconditionally stable higher-order accurate timestep integration algorithms Part 2. Second order equations. International Journal for NumericalMethods in Engineering, July, Vol. 45, No. 8, pp. 971-1006.

Fung, T.C., Chan, T.K., and Soh, C.K., 1999. Ultimate capacity of doubler plate-reinforcedtubular joints. ASCE Journal of Structural Engineering, August, Vol. 125, No. 8, pp. 891-899.

Fung, T.C., Soh C.K. and Qin, F., 1999. Seismic behaviour of completely overlap tubular joints.Proceedings of the 7th International Conference on Civil and Structural Engineering Computing(CIVIL-COMP99), 13-15 September, Oxford, England. Computer Techniques for Civil andStructural Engineering, Edited by B.H.V. Topping and B. Kumar, Civil-comp press, pp. 139-146.

Gasmo, J.M.*, Rahardjo, H. and Leong, E.C., 2000. Infiltration effects on stability of a residualsoil slope. Computer and Geotechnics, April, Vol. 26, pp. 145-165.

Gasmo, J.M.*, Rahardjo, H., Deutscher, M.S.* and Leong, E.C., 2000. Preliminary assessment ofslope stability with respect to rainfall-induced slope failures in “Unsaturated Soils for Asia“, eds.:Rahardjo, H. et al., Proceedings of the Asian Conference on Unsaturated Soils (UNSAT-ASIA2000) – From Theory to Practice, Singapore, 18-19 May, Balkema, pp. 783-788.

Goh, A.T.C., 1999. Genetic algorithm search for critical slip surface in multi-wedge stabilityanalysis. Canadian Geotechnical Journal, Vol. 36, No. 4, pp. 382-391.

Graham, N.*, Chen, X.G. and Jeyaseelan, S., 1999. Preparation of activated carbon from sewagesludge and waste materials. Proceedings of the International Conference on Civil and


Environmental Engineering, New Frontiers and Challenges, Bangkok, Thailand, 8-12 November,Vol. 1 (Part I) Environmental Engineering, pp. II-113-121.

Han, K.K.* and Rahardjo, H., 2000. “Mechanism of rain-induced slope failures in residual soils.”in “Unsaturated soils for Asia“, eds: Rahardjo, H. et al., Proceedings of the Asian Conference onUnsaturated Soils (UNSAT-ASIA 2000) – From Theory to Practice, Singapore, 18-19 May,Balkema, pp. 505-508.

Hao, H. and Ma, G.W.,* 1999. An investigation of the coupled torsional-pounding responses ofadjacent asymmetric structures. Proceedings of the 7th East Asia-Pacific Conference on StructuralEngineering & Construction, August 27-29, Kochi, Japan, pp. 788-793.

Hao, H. and Zhang, S.R., 1999. Quasi-stationary ground motion simulation and site amplificationcalculation. Journal of Earthquake Engineering and Engineering Vibration, December, Vol. 19,No. 4, pp. 33-42.

Hao, H. and Zhang, S.Y., 1999. Spatial ground motion effect on relative displacement of adjacentbuilding structures. International Journal of Earthquake Engineering and Structural Dynamics,Vol. 28, pp. 333-349.

Hao, H., Cheong, H.K. and Cui, S., 2000. Analysis of imperfect column buckling underintermediate velocity impact. International Journal of Solids and Structures, UK, Vol. 37, pp.5297-5313.

Hao, H., Liu, X.Y. and Jay Shen, 2000. Pounding response of adjacent buildings subjected tospatial earthquake ground excitations. International Journal of Advances in StructuralEngineering, May, Vol. 3, No. 2, pp. 145-162.

Hao, H., Ma, G.W.* and Seah, C.C., 1999. Parametric study of rock mass damage to blast loads.Proceedings of the 3rd Asia-Pacific Conference on Shock & Impact Loads on Structures, 24-26November, Singapore, pp. 149-154.

He, L.*, Leong, E.C. and Rahardjo, H., 1999. Rapid measurement of soil matric suction by time-domain reflectometry. Proceedings of 5th International Symposium on Field Measurements inGeomechanics, Leung et al. (Eds), A.A. Balkema, Singapore, 1-3 December, pp. 543-548.

Hulme, T.W.* and Zhao, J., 1999. Editorial: Tunnelling and underground space development inSingapore. Tunnelling and Underground Space Technology, Vol. 14, pp. 407.

Irawan, P., and Lim, C.S.*, 1999. Analysis of reinforced concrete slabs under punching shear.Proceedings of the 7th East Asia-Pacific Conference on Structural Engineering and Construction,Kochi, Japan, 27-29 August, Vol. 2, pp. 1247-1252.


Ivanov, V. and Kim, I.S.,* 1999. Microbiological monitoring of environmental engineeringsystems by fluorescencent in situ hybridization and fluorescence spectrometry. Proceedings of the2nd International Symposium on Advanced Environmental Monitoring, Kwangju, Korea, pp. 98-99.

Ivanov, V., 2000. Monitoring the bacterial neuston. In: Rapid Methods for Analysis of BiologicalMaterials in Environment (P.J. Stopa and M.A. Bartoszcze, eds.) Kluwer Academic Publishers, pp.67-72.

Ivanov, V., Kim, I.S.*, and Abella, C.A.,* 1999. Analysis of microbial diversity in environmentalsystems by specific and non-specific fluorescence in situ hybridization combined with fluorescencespectrometry. Proceedings of the 7th IAWQ Asia-Pacific Regional Conference. Taipei, Taiwan,18-20 October, pp. 304-309.

Ivanov, V.N. and Stabnikova, E.V.,* 1999. Use of data on the DNA G+C content in the study ofmolecular phylogeny of methanogenic archaebacteria. Microbiology (Moscow), Vol. 68, No. 5,pp. 710-715.

Jeyaseelan, S. and Chen, X.G., 2000. Aquous adsorption study for organic dyes by the activatedcarbon derived from sewage sludge. Proceedings of the World Congress and Exhibition of theAssociation on Resources, Recycling and Re-generation, Toronto Convention Center, Toronto,Canada, 2-5 June, CD-Rom.

Jeyaseelan, S. and Chen, X.G., 2000. Study of leaching and adsorption of heavy metals by theactivated carbon derived from sewage sludge. Proceedings of the World Congress and Exhibitionof the Association on Resources, Recycling and Re-generation, Toronto Convention Center,Toronto, Canada, 2-5 June, CD-Rom.

Kim, I.S.,* and Ivanov, V.N., 2000. Detection of nitrifying bacteria in activated sludge byfluorescent in situ hybridization and fluorescence spectrometry. World Journal of Microbiologyand Biotechnology, Vol. 16, No. 5, pp. 425-430.

Kim, I.S.,* Stabnikova, E. V.,* and Ivanov, V.N., 2000. Hydrophobic interactions within biofilmsof nitrifying and denitrifying bacteria in biofilters. Bioprocess Engineering 22, Vol. 4, pp. 285-290.

Krumholz, L.R.*, Harris, S.H.*, Tay, S.T. and Suflita, J.M.*, 1999. Characterization of twosubsurface H-2-utilizing bacteria, Desulfomicrobium hypogeium sp nov and Acetobacteriumpsammolithicum sp nov., and their ecological roles. Applied and Environmental Microbiology,Vol. 65, pp. 2300-2306.

Lan, S.R.*, Heng, L.*, Lok, T.S., Xiao, J.R.* and Lu, Xiaohua*, 2000. Explosive testing ofcomposite structural components. Proceedings of the DTG Technology Seminar - Building and


Infrastructure, Lands and Estates Organisation, Ministry of Defence, Singapore, February, pp. E1-E12.

Law, A.W.K. and Wang, H.W.,* 1999. Simultaneous velocity and scalar measurements ofaxisymmetric plume using combined DPIV and PLIF. Proceedings of the 3rd International PIVWorkshop, Santa Barbara, USA, pp. 445-450.

Law, A.W.K., 2000. Taylor dispersion of contaminants due to surface waves. Journal ofHydraulic Research, IAHR, Vol. 38, No. 1, pp. 41-48.

Lee, C.K., 2000. Automatic metric advancing front triangulation over curved surfaces.Engineering Computations, Vol. 17, No. 1, pp. 48-74.

Lee, C.K., Lie, S.T. and Wong, S.M., 1999. Model and mesh generation of cracked tubular joints.Proceedings of the European Conference on Computational Mechanics 99, Munich, Germany,31 August – 3 September, (CD-ROM Proceedings).

Lee, C.K., Lie, S.T., Huang, Z.W. and Wong, S.M., 2000. Finite element modelling of tubular Y-joint. Proceedings of the 4th Asia Pacific Structural Engineering & Construction Conference(APSEC 2000) Kuala Lumpur, Malaysia, 13-15 September, Vol. 2, pp. 315-322.

Lee, T.T.*, Rahardjo, H. and Leong, E.C., 1999. Simulation and natural runoff measurement onresidual hillslopes. Proceedings of the 5th International Symposium on Field Measurements inGeomechanics, Singapore, 1-3 December, pp. 387-391.

Leong, E.C., Rahardjo, H. and Low, B.K., 1999. Suction profiles and stability of residual soilslopes. Proceedings of the International Symposium on Slope Stability Engineering-IS-Shikoku’99, N. Yagi, T. Yamagami and J-C Jiang (Eds), Matsuyama, Shikoku, Japan, 8-11 November, pp. 387-392.

Leong, E.C., Rahardjo, H., Gasmo, J.M.* and Deutscher, M.S.,* 1999. Ground penetrating radartechnique for site charaterization in residual soils. Proceedings of the 11th Asian RegionalConference on Soil Mechanics and Geotechnical Engineering, Hong et al. (Eds), Balkema,Rotterdam, pp. 27-30.

Leong, W.K.*, Chu, J., and Teh, C.I., 2000. Liquefaction and instability of a granular fill material.Geotechnical Testing Journal, American Society for Testing and Materials, Vol. 23, No, 2, pp. 178-192.

Li, Bing and Tiong, R.L.K., 1999. Risk management model for international construction jointventures. Journal of Construction Engineering and Management, ASCE, Vol. 125, Issue No. 5, pp.377-384.


Li, Bing and Tiong, R.L.K., Wong, W.F. and Chew, D., 1999. Risk management in internationalconstruction joint ventures. Journal of Construction Engineering and Management, ASCE,July/August, Vol. 125, No. 4, pp. 277-284.

Li, H.B., Zhao, J. and Li, T.J.,* 1999. Triaxial compression tests of a granite at different strainrates and confining pressures. International Journal of Rock Mechanics and Mining Sciences, Vol.36, pp. 1057-1063.

Li, H.B., Zhao, J., Li, T.J. and Gao, J.G.,* 2000. Theoretical strength of a granite under dynamicuniaxial compressive load. Proceedings of the 4th North American Rock Mechanics Symposium,Seattle, USA.

Li, Q.M. and Jones, N.*, 1999. Shear and adiabatic shear failures in an impulsively loaded fullyclamped beam. International Journal of Impact Engineering, Vol. 22, pp. 589-607.

Li, Q.M. and Jones, N.*, 2000. On dimensionless numbers for dynamic plastic response of structuralmembers. Archive of Applied Mechanics, Vol. 70, pp. 245-254.

Li, Q.M. and Ma, G.W., 2000. Effects of damping on dynamic plastic response of circular plate.Key Engineering Materials, Vols. 177-180, pp. 285-290.

Li, Q.M., 1999. Dissipative flow model based on dissipative surface and irreversiblethermodynamics. Archive of Applied Mechanics, Vol. 69, pp. 379-392.

Li, Q.M., 2000. Continuity conditions at rigid-plastic interface of rigid-perfectly plastic structuralelements. International Journal of Solids and Structures, Vol. 37, pp. 3651-3665.

Li, Q.M., 2000. Energy correlations between a damaged macroscopic continuum and its subscale.International Journal of Solids and Structures, Vol. 37, pp. 4539-4556.

Li, Q.M., Mines, R.A.W.* and Birch, R.S.*, 1999. Combined strain rate and temperature effects oncompressive strength of Rohacell-51WF structural foam. Proceedings of the 3rd InternationalConference On Shock and Impact Loads on Structures, Singapore, November, pp. 221-226.

Li, Q.M., Mines, R.A.W.* and Birch, R.S.*, 2000. The crash behaviour of Rohacell-51WF foam.International Journal of Solid and Structures, Vol. 37, pp. 6321-6341.

Lie, S.T. and Yan, S., 1999. Weld magnification factors of non-load-carrying fillet welds.Proceedings of the 6th International Conference on Steel & Space Structures, 1-3 September,Singapore, pp. 279-288.


Lie, S.T., Chiew, S.P., Lee, C.K. and Huang, Z., 2000. Modelling arbitrary through thicknesscrack in a tubular T-joint. Proceedings of the 10th International Offshore and Polar EngineeringConference and Exhibition, Seattle, USA, 28 May - 2 June, pp. 53-58.

Lie, S.T., Xiang, Z., Wang, B. and Cen, Z., 2000. Experimental and numerical simulation of 3Dfatigue crack for plate-to-plate welded joints. International Journal of Fatigue, Vol. 22, pp. 411-424.

Lie, S.T., Xu, K. and Cen, Z., 1999. Multiple crack analysis using symmetric Galerkin boundaryelement method. Proceedings of the 4th Asia-Pacific Conference on Computational Mechanics, 15-17 December, Singapore, pp. 353-358.

Lie, S.T., Xu, K. and Cen, Z., 2000. Single domain cracks analysis using symmetric Galerkinboundary element methods. International Conference on Computational Engineering Science(ICES), Los Angles, California, USA, 21-25 August, pp. 93-98.

Lie, S.T., Yu, G. and Fan, S.C., 2000. Dynamic response of structural-acoustic interactions in timedomain by coupling boundary and finite elements. Proceedings of the 1st Conference: LocalDefense Research and Development Partnership, NUS, Faculty of Engineering, 14 March,Singapore.

Lie, S.T., Yu, G. and Fan, S.C., 2000. Further improvement to the stability of coupling BEM/FEMscheme for 2-D elastodynamic problems. Computational Mechanics, Vol. 25, No. 5, pp. 468-476.

Lie, S.T., Zhao, Z. and Yan, S., 2000. Two-dimensional and three-dimensional magnificationfactors, Mk, for non-load-carrying fillet welds cruciform joints. Engineering Fracture Mechanics,Vol. 65, pp. 435-453.

Lim, S.Y. and Cheng, N.S., 1999. Closure to prediction of live-bed scour at bridge abutments.Journal of Hydraulic Engineering, ASCE, Vol. 125, No. 9, pp. 985-986.

Lin, T.H.*, Wong, K.K.F. and Teng, N.J.*, 2000. Micromechanics of hysteresis loops of fatigue insingle crystal. Journal of Applied Mechanics, ASME, Vol. 67, pp. 338-343.

Liu, Q., Zhao, J., Lee, K.W. and Yang, K.S.,* 1999. Potential rock cavern development in theJurong sedimentary formation. Proceedings of the World Tunnel Congress '99, Oslo, Norway.

Lo, E.Y.M. and Lee, W.K., 2000. Wave scattering by a surface piercing membrane of finite extent .Proceedings of the 4th International Conference On Hydrodynamics, Yokohama, Japan, 7-9September, pp. 717-722.


Lo, E.Y.M., 2000. Performance of a flexible membrane wave barrier of a finite vertical extent.Coastal Engineering Journal, Japan Society of Civil Engineers, Vol. 42, No. 2, pp. 237-251.

Lok, T.S. and Cheng, Q.H.*, 1999. Closed-form solution for the free vibration of a truss-coresandwich panel. Proceedings of the 7th East Asia-Pacific Conference on Structural Engineering andConstruction, Kochi, Japan, August, pp. 285-290.

Lok, T.S. and Cheng, Q.H.*, 1999. Response of truss-core sandwich panels to air-blast loading.Proceedings of the 3rd International Conference on Shock and Impact Loads on Structures,Singapore, November, CI-Premier, pp. 257-266.

Lok, T.S. and Cheng, Q.H.*, 2000. Dynamic behavior of truss-core sandwich panel as anorthotropic thick plate. Proceedings of SPACE 2000, Aerospace Division, ASCE, Albuquerque,February, Ed. S.W. Johnson, et al., pp. 342-348.

Lok, T.S. and Cheng, Q.H.*, 2000. Elastic stiffness properties and behavior of truss-coresandwich panel. Journal of Structural Engineering, ASCE, May, Vol. 126, No. 5, pp. 552-559.

Lok, T.S. and Cheng, Q.H.*, 2000. Free vibration of clamped orthotropic sandwich panel. Journalof Sound and Vibration, USA, January, Vol. 229, No. 2, pp. 311-327.

Lok, T.S. and Xiao, J.R.*, 1999. Flexural strength assessment of steel fiber reinforced concrete.Journal of Materials in Civil Engineering, ASCE, August, Vol. 11, No. 3, pp. 188-196.

Lok, T.S. and Xiao, J.R.*, 1999. Steel fibre reinforced concrete panels exposed to air blastloading. Structures and Buildings, Journal of the Institution of Civil Engineers, UK, Paper 11927,November, Vol. 134, pp. 319-331.

Lok, T.S., Chong, W.H.* and Soh, T.B.*, 1999. Steel fibre reinforced concrete subjected tomultiple ballistic impact. Proceedings of the 3rd International Conference on Shock and ImpactLoads on Structures, Singapore, November, CI-Premier, pp. 241-256.

Lok, T.S., Xiao, J.R.* and Lan, S.R.*, 1999. Damage of steel fibre reinforced concrete structuressubjected to explosive loading. Proceedings of the 7th East Asia-Pacific Conference on StructuralEngineering and Construction, Kochi, Japan, August, pp. 1259-1264.

Lok, T.S., Xiao, J.R.*, Lan, S.R.* and Heng, L.*, 1999. Compressive cyclic response of steel fibrereinforced concrete. Proceedings of the Asia-Pacific Conference on Fibre Reinforced Concrete,Singapore, August, CI-Premier, pp. 99-108.


Low, B.K. and Teh, C.I., 1999. Probabilistic analysis of pile deflection under lateral loads.International Conference on Applications of Statistics and Probability (ICASP8), Sydney,Australia, December, Vol. 1, pp. 407-414.

Low, H.Y. and Hao, H., 1999. An investigation of dynamic responses of RC slabs with stochasticproperties subjected to blast loading. Proceedings of the 3rd Asia-Pacific Conference on Shock &Impact Loads on Structures, 24-26 November, Singapore, pp. 267-272.

Lu, Y., Hao, H., Ma, G.W.* and Zhou, Y.X.*, 2000. Response of model structures under simulatedunderground-blast induced excitations. Proceedings of the 12th World Conference on EarthquakeEngineering, 31 January – 4 February, Auckland, New Zealand, Paper 0972. (In CD-ROM)

Lu, Y., Hao, H., Ma, G.W.* and Zhou, Y.X.,* 1999. Effects of principal input frequency onstructural response to blasting induced ground excitations. Proceedings of the 3rd Asia-PacificConference on Shock & Impact Loads on Structures, 24-26 November, Singapore, pp. 273-280.

Luk, J.Y.K., 1999. Electronic road pricing in Singapore. Road & Transport Research Vol. 8, No.4, pp. 20-32.

Luk, J.Y.K., 1999. Incident detection on urban arterial roads. Proceedings of the 5th InternationalConference and Exhibition on City Planning, Transportation and Traffic Engineering, 16-18September, Singapore, pp. 1-10.

Ma, G.W.* and Hao, H., 1999. Investigation on limit angular velocity of annular disc.Proceedings of the 4th Asia-Pacific Conference on Computational Mechanics, 15-17 December,Singapore, pp. 399-404.

Ma, G.W.,* Hao, H. and Zhou, Y.X., 1999. Numerical investigation of in-plane failure of masonry.Proceedings of the 7th East Asia-Pacific Conference on Structural Engineering & Construction, 27-29 August, Kochi, Japan, pp. 417-422.

Ma, G.W.,* Hao, H., Lu, Y. and Zhou, Y.X.,* 1999. Damage assessment of infilled frame toground excitations. Proceedings of the 3rd Asia-Pacific Conference on Shock & Impact Loads onStructures, 24-26 November, Singapore, pp. 289-296.

Ma, G.W.,* Hao, H., Lu, Y. and Zhou, Y.X.,* 1999. Damage assessment of RC frame subjected tounderground blasting-induced ground motion. Proceedings of the 3rd Asia-Pacific Conference onShock & Impact Loads on Structures, 24-26 November, Singapore, pp. 281-288.

Ma, G.W.,* Hao, H., Lu, Y. and Zhou, Y.X.,* 2000. Damage assessment of reinforced concreteframe. Proceedings of the PARARI, An International Explosive Ordnance Symposium, Canberra,Australia, 10-12 November (in CD-ROM).


Megawati, K. and Pan, T.-C., 2000. Estimation of maximum credible ground motion intensity inSingapore due to long-distance Sumatra earthquakes. Invited Paper, Proceedings of the 2nd Multi-Lateral Workshop on Development of Earthquake and Tsunami Disaster Mitigation Technologies,Earthquake Disaster Mitigation Research Centre, 1–2 March, Kobe, Japan, pp. 323-331.

Menon, A.P.G. and Lam, S.H., 1999. Singapore's road pricing system – January 1994 toSeptember 1998. Research Report NTU/CTS/00-05, Centre for Transportation Studies

Menon, A.P.G., 2000. ERP in Singapore - A perspective one year on. Traffic Engineering +Control (tec), February, pp. 40-45.

Mines, R.A.W.*, Li, Q.M. and Birch, R.S.*, 2000. Static behaviour of transversely loaded CFRPlaminate panels subjected to in-plane tension. Strain, Vol. 36, pp. 71-80.

Ming, D.H.* and Chiew, Y.M., 2000. Experimental study for shoreline changes behind a detachedbreakwater. Journal of Waterway, Port, Coastal, and Ocean Engineering, ASCE, Vol. 126, No. 2,pp. 63-70.

Na, Y.M.*, Choa, V.,* Chang, M.F., Teh, C.I. and Bo Myint Win* 1999. Estimation ofgeotechnical parameters of granular soils from various in-situ tests. Proceedings of the 11th AsianRegional Conference on Soil Mechanics and Geotechnical Engineering, Seoul, August, Vol. 1, pp.277-280.

Ng, C.W.W.*, Chiu, C.F.* and Rahardjo, H., 2000. Behaviour of unsaturated loosely compactedfill materials in Hong Kong in “Unsaturated Soils for Asia“, eds.: Rahardjo, H. et al., Proceedingsof the Asian Conference on Unsaturated Soils (UNSAT-ASIA 2000) – From Theory to Practice,Singapore, 18-19 May, Balkema, pp. 551-556.

Nguyen, D.M., Chan, T.K. and Cheong, H.K., 1999. Effects of plate length on the strength ofreinforced concrete beams bonded with CFRP plates. East Asia-Pacific Conference on StructuralEngineering & Construction, Kochi, Japan, August, pp. 1277-1282.

Nguyen, D.M., Chan, T.K. and Cheong, H.K., 1999. Interaction behaviour between plate-adhesive-concrete and premature failures of FRP-strengthened beam. East Asia-PacificConference on Structural Engineering & Construction, Kochi, Japan, August, pp. 1289-1294.

Olszewski, P. and Tan, C.S.*, 1999. Walking lessons: pedestrian travel in Singapore. TrafficEngineering and Control, Vol. 40, No. 10, pp. 480-483.

Olszewski, P., 2000. Comparison of the HCM and Singapore models of arterial capacity.Proceedings of the 4th International Symposium on Highway Capacity, Transportation ResearchBoard, Maui, USA, pp. 87-98.


Pan, J.L.*, Goh, A.T.C., Wong, K.S. and Selby, A.R.*, 1999. Three-dimensional finite elementanalyses of passive pile behaviour. Proceedings of the 7th International Conference on Civil andStructural Engineering Computing, Oxford, September, pp. 1-6.

Pan, T.-C. and Li, J., 1999. Parallel processing for transient response of structures. Proceedingsof the International Conference on Parallel and Distributed Processing Techniques andApplications, 28 June – 1 July, Las Vegas, Nevada, USA, Vol. III, pp. 1430–1436.

Pan, T.-C. and Lu, Q.R., 2000. Response of buildings to long-distance earthquakes with siteeffects. Proceedings of the 12th World Conference on Earthquake Engineering, Auckland, NewZealand, January/February.

Pan, T.-C. and Megawati, K., 2000. Progress report on seismic hazard assessment of Singapore.Invited Paper, Proceedings of the Workshop on Ground Motion Modelling Techniques for AsianCountries, The University of Tokyo, 4 March, Tokyo, Japan, pp. 92-102.

Pan, T.-C. and Megawati, K., 2000. Seismic hazard assessment of Singapore. Invited Paper,Proceedings of the 2nd Multi-Lateral Workshop on Development of Earthquake and TsunamiDisaster Mitigation Technologies, Earthquake Disaster Mitigation Research Centre, 1-2 March,Kobe, Japan, pp. 87-92.

Pan, T.-C. and Zhu, Z.F., 1999. Seismic response of segmental buildings. Invited Paper,Proceedings of the International Post-SMiRT Conference Seminar on Seismic Isolation, PassiveEnergy Dissipation and Active Control of Vibrations of Structures, 23-25 August, KoreaEarthquake Engineering Research Center, Cheju, Korea, Vol. I, pp. 539–552.

Pan, T.-C., 1999. Characteristics of seismic risks in Southeast Asia. International Insurance andActuarial Journal, Vol. 3, No. 1, pp. 15-31.

Poh, T.Y.*, Goh, A.T.C., Wong, K.S., Wong, I.H.* and Poh, K.B.*, 1999. Determination ofbending moments in diaphragm walls. Proceedings of the 5th International Symposium on FieldMeasurements in Geomechanics, Singapore, December, pp. 223-228.

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CSE Research Bulletin No. 14. January 2001: Editoral Board

ISSN 0219-0370 January 2001 NO. 14

Shuy Eng Ban - Chairman Robyn Collins (Language editor) Carmel Heah (Language editor) Chin Chen Onn Fung Tat Ching Low Bak Kong James Luk Niall MacAlevey Tor Yam Khoon Wang Jin-Yuan Lee Chi King (Online edition)

ADDITIONAL COPIES AND ENQUIRIES

For general enquiries about this publication, and to request for hard copies, please write to :

The Dean School of Civil and Structural Engineering Nanyang Technological University Nanyang Avenue Singapore 639798 Tel : 7905264 Fax : 7910676 Email : [email protected]

Published by Dean School of Civil and Structural Engineering, Nanyang Technological University

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