1. Department of Civil and Environmental Engineering, Graduate School of EngineeringTohoku University Aoba‐yama 6‐6‐06 Sendai 980‐8579 Japan
2. Department of Civil and Environmental EngineeringUniversity of Miyazaki Gakuen Kibanadai‐Nishi 1‐1 Miyazaki 889‐2192 Japan
3. Department of Civil and Environmental Engineering, Graduate School of Science and EngineeringEhime University Bunkyo‐cho 3 Matsuyama 790‐8577 Japan