1. Department of Civil Engineering, Nagaoka National College of Technology, Nishi-Katakai 888, Nagaoka 940-8532, Japan
2. Department of Civil Engineering, Kure National College of Technology, Agaminami 2-2-11, Kure 737-8506, Japan
3. Department of Civil Engineering, Kochi National College of Technology, Monobe-Otsu 200-1, Nangoku 783-8508, Japan
4. Department of Environmental Systems Engineering, Nagaoka University of Technology, Kamitomioka 1603-1, Nagaoka 940-2188, Japan