1. Professor, School of Civil Engineering and Mechanics, Huazhong Univ. of Science and Technology, Wuhan, Hubei 430074, China (corresponding author).
2. Shaw Professor and Head, Dept. of Civil and Environmental Engineering, Pennsylvania State Univ., University Park, PA 16802.
3. Professor and Head, Dept. of Civil and Environmental Engineering, Colorado State Univ., Fort Collins, CO 80523.