1. Professor, Dept. of Civil Engineering, National Taipei Univ. of Technology, No. 1, Section 3, Chung-Hsiao E. Rd., Taipei 10608, Taiwan (corresponding author).
2. Professor, Dept. of Civil and Construction Engineering, National Taiwan Univ. of Science and Technology, No. 43, Section 4, Keelung Rd., Taipei 10607, Taiwan.