1. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., Pittsburgh, PA 15213.
2. 611 Auburn Ave., UP, Buffalo, NY 14222.formerly, Graduate Research Assistant, Carnegie Mellon Univ., Pittsburgh, PA 15213.
3. School of Civil and Environmental Engineering, Cornell Univ., Ithaca, NY 14853.formerly, Graduate Research Assistant, Carnegie Mellon Univ., Pittsburgh, PA 15213.
4. Professor, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., Pittsburgh, PA 15213 (corresponding author).