1. Ph.D. Candidate, Dept. of Civil & Environmental Engineering, Univ. of Maryland, College Park, MD 20742.
2. Professor, Dept. of Civil & Environmental Engineering, Univ. of Maryland, College Park, MD 20742.
3. Associate Professor, Dept. of Civil & Environmental Engineering, Univ. of Incheon, Incheon 406-772, South Korea (corresponding author).