1. Assistant Professor, Dept. of Civil and Environmental Engineering, 800 Lancaster Ave, Villanova Univ., Villanova, PA 19085, US.
2. Professor and Head, Dept. of Civil and Environmental Engineering, 1372 Campus Delivery, Colorado State Univ., Fort Collins, CO 80523-1372, US (Corresponding author), e-mail: shackel@engr.colostate.edu