1. Associate Professor, Dept. of Civil and Environmental Engineering, National Univ. of Kaohsiung, Kaohsiung 811, Taiwan, ROC (corresponding author).
2. Professor, Dept. of Civil Engineering, National Chung-Hsing Univ., Taichung 402, Taiwan, ROC.
3. Graduate Research Assistant, Dept. of Civil Engineering, National Chung-Hsing Univ., Taichung 402, Taiwan, ROC.