1. Postdoctoral Fellow, Japan Society for the Promotion of Science, Dept. of Urban and Civil Engineering, Faculty of Engineering, Ibaraki Univ., Nakanarusawa-cho 4-12-1, Hitachi 316-8511, Japan.
2. Professor, Dept. of Urban and Civil Engineering, Faculty of Engineering, Ibaraki Univ., Nakanarusawa-cho 4-12-1, Hitachi 316-8511, Japan.