1. Associate Professor, Dept. of Architecture and Environment System, Akita Prefectural Univ., Akita 015 0055, Japan (corresponding author).
2. Head, Design Section, Yokohama Port and Airport Technology Investigation Office, Ministry of Land, Infrastructure and Transport, Yokohama 221-0053, Japan.
3. Head, Structural Dynamics Division, Port and Airport Research Institute, Yokosuka 239 0826, Japan.