1. Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Utah, 122 South Central Campus Dr., 104 EMRO, Salt Lake City, UT 84112.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Wisconsin, 1415 Engineering Dr., 3216 Engineering Hall, Madison, WI 53706 (corresponding author). E-mail: noguera@engr.wisc.edu