1. Structural Engineer, Consoer Townsend Envirodyne Engineers, 303 East Wacker Dr., Suite 600, Chicago, IL 60601.
2. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois, 3108 Newmark Civil Engineering Laboratory, MC-250, 205 North Mathews Ave., Urbana, IL 61801 (corresponding author).
3. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois, 1116 Newmark Civil Engineering Laboratory, MC-250, 205 North Mathews Ave., Urbana, IL 61801.