1. Graduate Student, Dept. of Global Environment Engineering, Kyoto Univ., Kyoto 606-8501, Japan.
2. Professor, Dept. of Civil Engineering, Toyohashi Univ. of Technology, Toyohashi 441-8580, Japan.
3. Deceased December 14, 2001; formerly, Associate Professor, Dept. of Global Environment Engineering, Kyoto Univ., Kyoto 606-8501, Japan.