1. Professor, Dept. of Civil Engineering, National Taipei Univ. of Technology, No. 1, Chung-Hsiao E. Rd., Sec. 3, Taipei 10608, Taiwan (corresponding author).
2. Dept. of Civil Engineering, National Taipei Univ. of Technology, No. 1, Chung-Hsiao E. Rd., Sec. 3, Taipei 10608, Taiwan.