1. Ph.D. Candidate, School of Civil Engineering, Beijing Jiaotong Univ., Beijing 100044, China.
2. Master Student, School of Civil Engineering, Beijing Jiaotong Univ., Beijing 100044, China.
3. Master Student, School of Railway Engineering, Iran Univ. of Science and Technology, Tehran 16846-13114, Iran.
4. Professor, School of Civil Engineering, Beijing Jiaotong Univ., No. 3, Shangyuancun, Haidian District, Beijing 100044, China (corresponding author).