1. Doctoral Student, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 N. Mathews Ave., Room 3148, Urbana, IL 61801.
2. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 N. Mathews Ave., Room 2207, Urbana, IL 61801 (corresponding author).