1. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois, Urbana-Champaign, IL 61801 (corresponding author).
2. Ph.D. Student, Dept. of Civil and Environmental Engineering, Univ. of Illinois, Urbana-Champaign, IL 61801.
3. Lecturer, Institute for Infrastructure Engineering, Univ. of Western Sydney, Penrith, NSW 2751, Australia.
4. Associate Professor, Dept. of Civil and Environmental Engineering, Seoul National Univ., Seoul 151-742, Korea.
5. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois, Urbana-Champaign, IL 61801.