1. Professor, School of Civil Engineering, Central South Univ., Changsha, Hunan 410075, China.
2. Ph.D. Student, School of Civil Engineering, Central South Univ., Changsha, Hunan 410075, China; Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Univ. of California, Berkeley, Berkeley, CA 94720 (corresponding author).
3. Graduate Student, School of Civil Engineering, Central South Univ., Changsha, Hunan 410075, China.
4. Professor, School of Science, Engineering, and Technology, Pennsylvania State Univ. Harrisburg, Middletown, PA 17057.