1. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Hong Kong Polytechnic Univ., Hung Hom, Kowloon, Hong Kong SAR, P. R. China.
2. Professor, Dept. of Civil and Environmental Engineering, Hong Kong Polytechnic Univ., Hung Hom, Kowloon, Hong Kong SAR, P. R. China (corresponding author).