1. Assistant Professor, School of Civil and Construction Engineering, Oregon State Univ., 220 Owen Hall, Corvallis, OR 97331 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Washington, Box 352700, Seattle, WA 98195.
3. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Washington, Box 352700, Seattle, WA 98195.
4. Professor Emeritus, Dept. of Civil and Environmental Engineering, Univ. of Washington, Box 352700, Seattle, WA 98195.