1. Doctoral Student, Dept. of Civil Engineering, Shanghai Jiaotong Univ., No. 800 Dongchuan Rd., Shanghai 200240, P.R. China.
2. Associate Professor, Dept. of Civil Engineering, Shanghai Jiaotong Univ., No. 800 Dongchuan Rd., Shanghai 200240, P.R. China (corresponding author).
3. Engineer, Shanghai Nuclear Engineering Research and Design Institute, No. 29 Hongcao Rd., Shanghai 200240, P.R. China.
4. Chief Engineer, Shanghai Nuclear Engineering Research and Design Institute, No.29 Hongcao Rd., Shanghai 200240, P.R. China.