1. Postdoctoral Fellow, Dept. of Civil and Environmental Engineering, Univ. of Michigan, Ann Arbor, MI 48109-2125.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Michigan, Ann Arbor, MI 48109-2125 (corresponding author).
3. Leader, Structures Group, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8611.