1. Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of California at Davis, One Shields Ave., Davis, CA 95616; formerly, Graduate Research Assistant, Dept. of Structural Engineering, Univ. of California, San Diego, La Jolla, CA 92093.
2. Professor, Dept. of Structural Engineering, MC-0085, Univ. of California, San Diego, La Jolla, CA 92093-0085 (corresponding author).