1. School of Civil Engineering, Southwest Jiaotong Univ., Chengdu, Sichuan, China
2. Professor, School of Civil Engineering, Southwest Jiaotong Univ., Chengdu, Sichuan, China
3. School of Civil Engineering, Southwest Jiaotong Univ., Sichuan, Chengdu, China
4. School of Civil Engineering, Southwest Jiaotong Univ., Chengdu, Sichuan, China (corresponding author).