1. Associate Professor, Dept. of Civil and Environmental Engineering, Nagaoka Univ. of Technology, Nagaoka, Niigata 940-2118, Japan (corresponding author).
2. Doctoral Student, Dept. of Civil and Environmental Engineering, Nagaoka Univ. of Technology, Nagaoka, Niigata 940-2118, Japan.
3. Technical Staff, Dept. of Civil and Environmental Engineering, Nagaoka Univ. of Technology, Nagaoka, Niigata 940-2118, Japan.