1. Assistant Professor, Dept. of Civil and Environmental Engineering, California Polytechnic State Univ., San Luis Obispo, CA 93407 (corresponding author).
2. Engineer, Pacific Gas and Electric Company, San Francisco, CA 94105; formerly, Research Assistant, Dept. of Civil and Environmental Engineering, California Polytechnic State Univ., San Luis Obispo, CA 93407.
3. Assistant Professor, Dept. of Civil Engineering, Case Western Reserve Univ., Cleveland, OH 44106.