1. Postdoctoral Fellow, Dept. of Civil and Environmental Engineering, Colorado School of Mines, 1012 14th St., Golden, CO 80401.
2. Professor, Dept. of Civil and Environmental Engineering, Colorado School of Mines, 1012 14th St., Golden, CO 80401 (corresponding author).
3. Associate Professor, Dept. of Structural Engineering, Univ. of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093.