1. Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, One Shields Ave., Davis, CA 95616.
2. Assistant Professor, Dept. of Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto, ON, Canada M5S 1A4.
3. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, 3101 Engineering Bldg. III, One Shields Ave., Davis, CA 95616 (corresponding author).