1. Professor, Dept. of Bridge Engineering, Civil Engineering School, Southwest Jiaotong Univ., Chengdu, Sichuan 610031, China (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, CA 95616.
3. Ph.D. Student, Dept. of Bridge Engineering, Civil Engineering School, Southwest Jiaotong Univ., Chengdu, Sichuan 610031, China.
4. Ph.D. Student, Dept. of Bridge Engineering, Civil Engineering School, Southwest Jiaotong Univ., Chengdu, Sichuan 44000, China.