1. Professor, Dept. of Civil Engineering, National Chung Hsing Univ., Taichung 402, Taiwan (corresponding author).
2. Senior Assistant, Dept. of Civil Engineering, National Chung Hsing Univ., Taichung 402, Taiwan.
3. Professor, Dept. of Civil Engineering, National Chung Hsing Univ., Taichung 402, Taiwan.