1. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801 (corresponding author).
2. Research Assistant Professor, Dept. of Civil & Environmental Engineering, Washington State Univ., Pullman, WA 99163.
3. Visiting Scholar, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801.