1. Lecturer in Civil Engineering, School of Engineering, RMIT Univ., Melbourne, VIC 3001, Australia (corresponding author).
2. Professor of Civil Engineering, Dept. of Engineering, Univ. of Cambridge, Trumpington St., Cambridge CB2 1PZ, U.K.
3. Professor of Civil Engineering, Dept. of Civil and Environmental Engineering, Cornell Univ., Room 273 Hollister Hall, Ithaca, NY 14853.
4. Group Leader, Fundamental Technology Research Institute, Tokyo Gas Co., Ltd., Yokohama 230-0045, Japan.