1. Research Fellow, School of Civil and Environmental Engineering, Nanyang Technological Univ., 50 Nanyang Ave., Singapore 639798.
2. Professor, School of Engineering and Information Technology, Univ. of New South Wales, Canberra, Northcott Dr., Campbell, ACT 2600, Australia.
3. Professor, School of Civil and Environmental Engineering, Nanyang Technological Univ., 50 Nanyang Ave., Singapore 639798 (corresponding author).