1. School of Civil and Environmental Engineering, Nanyang Technological Univ., Block N1, #1B-36 Nanyang Ave., 63978 Singapore (corresponding author). E-mail: chrahardjo@ntu.edu.sg
2. School of Civil and Environmental Engineering, Nanyang Technological Univ., Block N1, #1B-36 Nanyang Ave., 63978 Singapore.
3. Dept. of Civil Engineering, Univ. Teknologi Petronas, Bandar Seri Iskandar, 31750 Tronoh, Perak Darul Ridzuan, Malaysia.