1. Professor and Chairman, Dept. of Civil Engineering, National Chiao Tung Univ., Hsinchu, Taiwan 30010, R.O.C. (corresponding author).
2. Graduate Student, Dept. of Civil Engineering, National Chiao Tung Univ., Hsinchu, Taiwan 30010, R.O.C.
3. Ph.D. Candidate, Dept. of Civil Engineering, National Chiao Tung Univ., Hsinchu, Taiwan 30010, R.O.C.