1. Professor, College of Civil Engineering, Hunan Univ., Changsha, Hunan 410082, China.
2. Lecturer, College of Civil Engineering, Hunan Univ., Changsha, Hunan 410082, School of Civil Engineering and Architecture, Changsha Univ. of Science and Technology, Changsha, Hunan 410076, China (corresponding author).
3. Associate Professor, College of Civil Engineering, Hunan Univ., Changsha, Hunan 410082, China.
4. Senior Engineer, Design Institute for Communic. Planning and Survey, Changsha, Hunan 410011, China.