1. Professor, Dept. of Civil and Construction Engineering, National Taiwan Univ. of Science and Technology, 43 Keelung Rd., Daan District, Taipei 106, Taiwan.
2. Ph.D. Candidate, Dept. of Civil and Construction Engineering, National Taiwan Univ. of Science and Technology, 43 Keelung Rd., Daan District, Taipei 106, Taiwan (corresponding author).