1. Research Professor, Civil, Environmental & Architectural Engineering, Korea Univ., 335 Engineering Building, Seoul 136-701, South Korea.
2. Associate Professor, Dept. of Civil & Environmental Engineering, Univ. of Washington, 214B More Hall, Seattle, WA 98195.
3. Professor, Dept. of Civil & Environmental Engineering, Univ. of Washington, 233B More Hall, Seattle, WA 98195 (corresponding author).
4. Professor, Civil, Environmental & Architectural Engineering, Korea Univ., 305 Engineering Building, Seoul 136-701, South Korea.