1. Research Associate, Dept. of Civil and Environmental Engineering, Saitama Univ., 255 Simo-Okubo, Sakura-Ku, Saitama 338-8570, Saitama, Japan.
2. Professor, Dept. of Civil and Environmental Engineering, Saitama Univ., 255 Simo-Okubo, Sakura-Ku, Saitama 338-8570, Saitama, Japan.