1. Lecturer, Dept. of Civil Engineering, Rajamangala Institute of Technology, Patumthani 12110, Thailand.
2. Professor, Dept. of Civil Engineering, King Mongkut’s Univ. of Technology Thonburi, Pracha-utid Rd., Bangmod, Toongkru, Bangkok 10140, Thailand (corresponding author).
3. Professor, Dept. of Civil Engineering, National Univ. of Singapore, Kent Ridge, Singapore 119260.