1. Post-Doctoral Fellow, Division of Structural and Geotechnical Engineering, Hokkaido Univ., Sapporo 060-8628, Japan.
2. Professor, Division of Structural and Geotechnical Engineering, Hokkaido Univ., Sapporo 060-8628, Japan.
3. Research Associate, Division of Structural and Geotechnical Engineering, Hokkaido Univ., Sapporo 060-8628, Japan.