1. Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews Ave., Urbana, IL 61801 (corresponding author).
2. Professor, Dept. of Civil Engineering, Univ. of Illinois at Urbana-Champaign, 1212 NCEL, 205 North Mathews Ave., Urbana, IL 61801.