1. Professor, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 Univ. Rd., Hsinchu, Taiwan 300, Republic of China.
2. Ph.D. Candidate, Dept. of Civil Engineering, National Chiao Tung Univ., Hsinchu, Taiwan, Republic of China (corresponding author).
3. Post-Doctor, Dept. of Civil Engineering, National Chiao Tung Univ., Hsinchu, Taiwan, Republic of China.