1. Assistant Professor, Dept. of Civil and Environmental Engineering, Waseda Univ., Shinjuku-ku, Tokyo 169-8555, Japan.
2. Professor, Dept. of Civil and Environmental Engineering, Waseda Univ., Shinjuku-ku, Tokyo 169-8555, Japan (corresponding author).
3. Associate Professor, Dept. of Civil and Environmental Engineering, Maebashi Institute of Technology, Maebashi-shi Gunma 371-0816, Japan.
4. Associate Professor, Dept. of Civil and Environmental Engineering, Waseda Univ., Shinjuku-ku, Tokyo 169-8555, Japan.
5. Lecturer, School of Civil Engineering and Architecture, Changsha Univ. of Science and Technology, Hunan 410004, China; formerly, Visiting Scholar, Waseda Univ.