1. Doctoral Candidate, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801.
2. Nathan M. and Anne M. Newmark Endowed Chair of Civil Engineering, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801 (corresponding author).