1. Res. Assoc., Dept. of Civ. Engrg., Kyoto Univ., Yoshida, Sakyoku, Kyoto 606-8501, Japan.
2. Assoc. Prof., Dept. of Civ. Engrg., Kyoto Univ., Yoshida, Sakyoku, Kyoto 606-8501, Japan.
3. Prof., Dept. of Civ. Engrg., Kyoto Univ., Yoshida, Sakyoku, Kyoto 606-8501, Japan.