1. Ph.D. Candidate, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 University Rd., Hsinchu, Taiwan 300, ROC (corresponding author).
2. Associate Professor, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 University Rd., Hsinchu, Taiwan 300, ROC.
3. Professor, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 University Rd., Hsinchu, Taiwan 300, ROC.