1. Academic Staff, Centre for Science and Mathematics, Republic Polytechnic, Singapore 738964; formerly, School of the Built Environment Heriot-Watt Univ., Edinburgh EH14 4AS, U.K.
2. Professor, Dept. of Civil Engineering Systems, Heriot-Watt Univ., Edinburgh EH14 4AS, U.K. (corresponding author). E-mail: p.w.jowitt@hw.ac.uk