1. Research Fellow, Fonds National de la Recherche Scientifique and Univ. catholique de Louvain, Belgium.
2. Assistant Professor, Dept. of Civil Engineering, Indian Institute of Technology, Bombay, Mumbai, India - 400 076.
3. Graduate Student, Dept. of Civil Engineering and Hydrotech Res. Institute, National Taiwan Univ., 258 Chow-Shan Rd., Taipei 10617, Taiwan.
4. Professor, Dept. of Civil Engineering and Hydrotech Res. Institute, National Taiwan Univ., 258 Chow-Shan Rd., Taipei 10617, Taiwan (corresponding author).
5. Professor, Dept. of Civil Engineering, Univ. catholique de Louvain, Belgium.