1. Research Fellow, School of Civil and Environmental Engineering, Nanyang Technological Univ., Nanyang Ave., Singapore 639798.
2. Associate Professor, School of Civil and Environmental Engineering, Nanyang Technological Univ., Nanyang Ave., Singapore 639798 (corresponding author).
3. Associate Professor, Dept. of Civil and Resource Engineering, The Univ. of Western Australia, 35 Stirling Hwy., Crawley, WA 6009, Australia.