1. Department of Civil Engineering, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi-ku, Osaka 535-0085, Japan
2. River Structure Section, River and Coastal Engineering Division, NEWJEC, 1-20-19 Shimanouchi, Chyuo-ku, Osaka 542-0082, Japan
3. Research Center for Urban Safety and Security, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan