1. Professor, Dept. of Civil Engineering, National Cheng Kung Univ., Tainan, Taiwan 70101, R.O.C.
2. Dept. of Civil Engineering, National Cheng Kung Univ., Tainan, Taiwan 70101, R.O.C. (corresponding author).
3. Dept. of Civil Engineering, National Cheng Kung Univ., Tainan, Taiwan 70101, R.O.C.