1. Assistant Professor, School of Civil and Environmental Engineering, Nanyang Technological Univ., Singapore 639798 (corresponding author).
2. PhD candidate, School of Civil and Environmental Engineering, Nanyang Technological Univ., Singapore 639798.
3. Lecturer, Dept. of Mechanical, Aerospace, and Manufacturing Engineering, UMIST, P.O. Box 88, Manchester M60 1QD, U.K.