1. Ph.D. Candidate, School of Civil Engineering, Southwest Jiaotong Univ., 111 North Section One, Second Ring Rd., Chengdu 610031, China.
2. Professor, School of Civil Engineering, Southwest Jiaotong Univ., 111 North Section One, Second Ring Rd., Chengdu 610031, China (corresponding author).
3. Ph.D. Candidate, Department of Civil Engineering, Missouri Univ. of Science and Technology, 1401 North Pine St., Rolla, MO 65401.