1. Professor, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan.
2. PhD candidate, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan.
3. Graduate Research Assistant, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan.