1. Professor, Dept. of Civil Engineering, Kobe Univ., 1-1 Rokkodai, Nada, Kobe 657-8501, Japan (corresponding author).
2. Associate Professor, Dept. of Environmental and Civil Engineering, Okayama Univ., 3-1-1 Tsushima-naka, Okayama 700-8530, Japan.
3. Engineer, Construction Technology Institute (CTI) Co. Ltd., 2-31 Hachobori, Nakaku, Hitorsima 730-0013, Japan.
4. Engineer, Hanshin Railway Co. Ltd., 116 Kitashirouchi, Amagasaki 660-0826, Japan.