1. Doctoral Candidate, Dept. of Civil and Environmental Engineering, Univ. of Illinois, Urbana, IL 61801.
2. Nathan M. and Anne M. Newmark Endowed Chair in Civil Engineering, Univ. of Illinois, Urbana, IL 61801 (corresponding author).
3. William J. and Elaine F. Hall Endowed Professor in Civil and Environmental Engineering, Univ. of Illinois, Urbana, IL 61801.