1. Professor, Dept. of Civil Engineering, Univ. of Washington, 233B More Hall, Seattle, WA 98195-2700 (corresponding author).
2. Associate Professor, Dept. of Civil Engineering, Univ. of Washington, 214B More Hall, Seattle, WA 98195-2700.
3. Engineer, Reid Middleton, 728 134th St. SW, Suite 200, Everett, WA 98204; formerly, Graduate Student, Dept. of Civil Engineering, Univ. of Washington, Seattle, WA.