1. Professor, Dept. of Bridge Engineering, Southwest Jiaotong Univ., Chengdu 610031, Sichuan, P. R. China (corresponding author).
2. Ph.D. Candidate, Dept. of Bridge Engineering, Southwest Jiaotong Univ., Chengdu 610031, Sichuan, P. R. China.
3. Edwin B. and Norma S. McNeil Distinguished Professor, Dept. of Civil and Environmental Engineering, Louisiana State Univ., Baton Rouge, LA 70803.
4. Professor, Dept. of Bridge Engineering, Southwest Jiaotong Univ., 610031, Chengdu, Sichuan, P. R. China.