1. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 2204 Newmark Laboratory, 205 North Mathews Ave., MC-250, Urbana, IL 61801.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 2209 Newmark Laboratory, 205 North Mathews Ave., MC-250, Urbana, IL 61801 (corresponding author).
3. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 1212 Newmark Laboratory, 205 North Mathews Ave., MC-250, Urbana, IL 61801.