1. Professor, Dept. of Civil and Environmental Engineering, Univ. of Michigan, Ann Arbor, MI 48109-2125 (corresponding author).
2. Lecturer, School of Civil Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150090, P.R. China; formerly, Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Univ. of Michigan, Ann Arbor, MI.
3. Professor and Chair, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, CA 95616.