1. Professor, Dept. of Civil Engineering, National Cheng Kung Univ., 1 University Rd., Tainan 701, Taiwan (corresponding author).
2. Ph.D. Candidate, Dept. of Civil Engineering, National Cheng Kung Univ., 1 University Rd., Tainan 701, Taiwan.
3. Associate Professor, College of Civil Engineering, 1 Luhun St., Changsha, Hunan 410082, P.R. China.
4. Research Associate, Dept. of Civil Engineering, National Cheng Kung Univ., 1 University Rd., Tainan 701, Taiwan.