1. Professor, Dept. of Structural Engineering, State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji Univ., Shanghai 200092, China.
2. Graduate Student, Dept. of Structural Engineering, Tongji Univ., Shanghai 200092, China.
3. Professor, Dept. of Civil and Environmental Engineering, Univ. of Maryland, College Park, MD 20742 (corresponding author).