1. Assistant Professor, Dept. of Civil, Arch. and Environment Engineering, Missouri Univ. of Science and Technology, Rolla, MO 65409; formerly, Graduate Resident Assistant, Dept. of Structural Engineering, Univ. of California-San Diego, La Jolla, CA 92093.
2. Professor, Dept. of Structural Engineering, Univ. of California-San Diego, La Jolla, CA 92093 (corresponding author).