1. Technical Division I, ITC Corporation, 1-7-18, Okubo, Shinjuku-ku, Tokyo, 169-0072, Japan (corresponding author).
2. Professor, Dept. of Civil Engineering, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro-ku, Tokyo 152-8552, Japan.
3. General Manager, Construction and Technical Development Division, Oriental Shiraishi Corporation, 2-1-1, Hirakawa-cho, Chiyoda-ku, Tokyo 102-0093, Japan.