1. Research Associate, Dept. of Civil and Environmental Engineering, Nagaoka Univ. of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan.
2. Professor, Dept. of Civil and Environmental Engineering, Nagaoka Univ. of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188, Japan.
3. Senior Research Engineer, Technical Research Institute, Hazama Co., Ltd., 515-1 Karima, Tsukuba, Ibaragi 305-0822, Japan.