1. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 1351 Beal Ave., Ann Arbor, MI 48109.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 1351 Beal Ave., Ann Arbor, MI 48109 (corresponding author).
3. Professor, Dept. of Aerospace Engineering, Univ. of Michigan, 1320 Beal Ave., Ann Arbor, MI 48109.