1. Graduate Student, School of Civil and Environmental Engineering, Cornell Univ., Hollister Hall, Ithaca, NY 14853-3501.
2. Senior Lecturer, School of Civil and Environmental Engineering, Cornell Univ., Hollister Hall, Ithaca, NY 14853-3501 (corresponding author).
3. Professor, School of Civil and Environmental Engineering, Cornell Univ., Hollister Hall, Ithaca, NY 14853-3501.