1. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 2340 G. G. Brown, 2350 Hayward, Ann Arbor, MI 48109.
2. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Michigan, 2340 G. G. Brown, 2350 Hayward, Ann Arbor, MI 48109 (corresponding author).