1. Ph.D. Student, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, IL 61801; formerly, Graduate Student, Korea Univ., Seoul 136-701, Korea.
2. Ph.D. Student, School of Civil, Environmental, and Architectural Engineering, Korea Univ., Seoul 136-701, Korea.
3. Associate Professor, School of Civil, Environmental, and Architectural Engineering, Korea Univ., Seoul 136-701, Korea (corresponding author).