1. Assistant Professor, Dept. of Civil and Construction Engineering, National Taiwan Univ. of Science and Technology, No. 43, Sec. 4, Keelung Rd., Taipei City 106, Taiwan, R.O.C. (corresponding author).
2. Postgraduate Student, Dept. of Civil and Construction Engineering, National Taiwan Univ. of Science and Technology, No. 43, Sec. 4, Keelung Rd., Taipei City 106, Taiwan, R.O.C.