1. Lecture, College of Civil and Transportation Engineering, Hohai Univ., No. 1, Xikang Rd., Nanjing, Jiangsu 210098, P.R. China (corresponding author).
2. Professor, College of Civil and Transportation Engineering, Hohai Univ., No. 1, Xikang Rd., Nanjing, Jiangsu 210098, P.R. China.