1. Associate Professor, College of Civil Engineering, Fuzhou Univ., Fuzhou, Fujian Province 350108, P.R. China.
2. Professor, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, P.R. China (corresponding author).
3. Lecturer, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, P.R. China.
4. Professor, Institute for Infrastructure Engineering, Western Sydney Univ., Penrith, NSW 2751, Australia.