1. Johnson Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Berkeley, CA 94720-1710.
2. Associate Professor, Dept. of Civil and Environmental Engineering, California Polytechnic State Univ., San Luis Obispo, CA 93407.
3. Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of California, Berkeley, CA 94720-1710.