1. Graduate Student, Dept. of Civil and Environmental Engineering, 4105 Seamans Center for the Engineering Arts and Sciences, The Univ. of Iowa, Iowa City, IA 52242.
2. Allen S. Henry Chair Professor, Dept. of Civil and Environmental Engineering, 4119 Seamans Center for the Engineering Arts and Sciences, The Univ. of Iowa, Iowa City, IA 52242 (corresponding author).