1. State Key Laboratory of Safety and Health for In-service Long Span Bridges; Jiangsu Transportation Institute; Nanjing 211112 China
2. Department of Civil Engineering; The University of Tokyo; Tokyo 113-8656 Japan
3. Department of Civil Engineering; Yokohama National University; Yokohama 240-8501 Japan
4. Institute of Advanced Sciences; Yokohama National University; Yokohama 240-8501 Japan