1. Research Fellow, Nanyang Technological Univ., School of Civil and Environmental Engineering, BLK. N1, No. B1b-09, 50 Nanyang Ave., Singapore 639798 (corresponding author).
2. Associate Professor, Nanyang Technological Univ., School of Civil and Environmental Engineering, BLK. N1, No. 01a-37, 50 Nanyang Ave., Singapore 639798.