1. Ph.D. Candidate, Dept. of Civil Engineering, Univ. of Hong Kong, Pokfulam Rd., Hong Kong; and Dept. of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, U.K. (corresponding author).
2. Professor, Dept. of Civil Engineering, Univ. of Hong Kong, Pokfulam Rd., Hong Kong.
3. Professor, Dept. of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, U.K.