1. Ph.D. Candidate, Dept. of Structural Engineering, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P.R. China.
2. Assistant Professor, Dept. of Structural Engineering, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P.R. China.
3. Professor, Dept. of Civil, Architectural and Environmental Engineering, Univ. of Colorado, Boulder, CO 80309.
4. Professor, Dept. of Structural Engineering, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P.R. China (corresponding author).
5. Professor, Dept. of Structural Engineering, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P.R. China.