1. Structural Engineer, Skidmore, Owings and Merrill LLP, 1 Front St., San Francisco, CA 94111.
2. Associate Professor, Newmark Civil Engineering Laboratory, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, MC-250, 205 North Mathews Ave., Urbana, IL 61801 (corresponding author).