1. Senior Bridge Engineer, Office of Earthquake Engineering, Caltrans, 1801 30th St., Sacramento, CA 95816.
2. Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of California, Los Angeles, CA 90095.
3. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Los Angeles, CA 90095.
4. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Los Angeles, CA 90095 (corresponding author).