1. Professor, Dept. of Civil Engineering, National Univ. of Singapore, Blk E1A, #07-03, 1 Engineering Dr. 2, Singapore 117576, Singapore.
2. Research Scholar, Dept. of Civil Engineering, National Univ. of Singapore, Blk E1A, #07-03, 1 Engineering Dr. 2, Singapore 117576, Singapore (corresponding author).