1. Ph.D. Candidate, College of Civil Engineering, Hunan Univ., Changsha 410082, P.R. China.
2. Associate Professor, College of Civil Engineering, Hunan Univ., Changsha 410082, P.R. China (corresponding author).
3. Graduate Research Assistant, College of Civil Engineering, Hunan Univ., Changsha 410082, P.R. China.