1. Professor, Dept. of Civil Engineering, National Taiwan Univ., 1, Roosevelt Rd., Section 4, Taipei 106, Taiwan, R.O.C. (corresponding author).
2. Professor, Dept. of Engineering Science and Ocean Engineering, National Taiwan Univ., 1, Roosevelt Rd., Section 4, Taipei 106, Taiwan, R.O.C.
3. Graduate Student, Dept. of Civil Engineering, National Taiwan Univ., 1, Roosevelt Rd., Section 4, Taipei 106, Taiwan, R.O.C.