1. Professor, Institute of Structural Engineering, Zhejiang Univ., Hangzhou 310058, P.R. China.
2. Ph.D. Candidate, Institute of Structural Engineering, Zhejiang Univ., Hangzhou 310058, P.R. China.
3. Associate Professor, Institute of Structural Engineering, Zhejiang Univ., Hangzhou 310058, P.R. China (corresponding author).
4. Engineer, Henan Electric Power Testing and Research Institute, No. 87, Songshan Rd., Zhenzhou, Henan 450052, P.R. China.