1. Associate Professor, College of Civil Engineering, Hunan Univ., Changsha, Hunan Province 410082, P.R. China; formerly, Postdoctoral Research Engineer, Drexel Univ., Philadelphia, PA 19104 (corresponding author).
2. Drexel Univ., Philadelphia, PA 19104.
3. Associate Professor, Drexel Univ., Philadelphia, PA 19104.
4. John Roebling Professor, Drexel Univ., Philadelphia, PA 19104.