1. Associate Professor, Dept. of Civil Engineering, Shanghai Jiao Tong Univ., Shanghai 200240, China.
2. Dept. of Civil Engineering, Shanghai Jiao Tong Univ., Shanghai 200240, China.
3. Professor, Dept. of Civil Engineering, Shanghai Jiao Tong Univ., Shanghai 200240, China.
4. Associate Professor, Dept. of Civil Engineering and Engineering Mechanics, Univ. of Arizona, Tucson, AZ 85721 (corresponding author).