1. Professor, Dept. of Civil Engineering, Univ. of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
2. Former Research Fellow, Japan Society for the Promotion of Science for Young Scientists, Dept. of Civil Engineering, Univ. of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
3. Chief Researcher, BMG Corp., Nakase, Mihama-ku, Chiba 261-7125, Japan.