1. Professor, Dept. of Civil Engineering, National Taiwan Univ., Taipei 106, Taiwan.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Houston, Houston, TX 77204-4003.
3. Assistant Professor, Dept. of Civil Engineering, National Yunlin Univ. of Science and Technology, Yunlin 123, Taiwan.
4. Graduate Student, Dept. of Civil Engineering, National Cheng-Kung Univ., Tainan 701, Taiwan.
5. Graduate Student, Dept. of Civil Engineering, National Taiwan Univ., Taipei 106, Taiwan.