1. Louisiana State Univ., Dept. of Civil and Environmental Engineering, Baton Rouge, LA 70803, US (Corresponding author), e-mail: cwillson@lsu.edu
2. Colorado School of Mines, Dept. of Civil and Environmental Engineering, Golden, CO 80401, US.
3. Univ. of Wisconsin, Dept. Civil and Environmental Engineering, Madison, WI 53706, US.