1. Professor, Dept. of Civil Engineering, Zhejiang Univ., Hangzhou 310058, China.
2. Ph.D. Student, Dept. of Civil Engineering, Zhejiang Univ., Hangzhou 310058, China.
3. Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of South Carolina, Columbia, SC 29208.
4. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801 (corresponding author).