1. Dept. of Civil and Environmental Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokusaka, Kanagawa 239-8686, Japan.
2. Professor, Dept. of Civil Engineering, Univ. of British Columbia, 2324 Main Mall, Vancouver BC, Canada V6T 1Z4.
3. Graduate Student, Dept. of Civil Engineering, Univ. of British Columbia, 2324 Main Mall, Vancouver BC, Canada V6T 1Z4.