1. Postdoctoral Associate, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139.
2. Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of New Hampshire, Durham, NH 03824.
3. Chair and Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of New Hampshire, Durham, NH 03824.
4. Professor, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139 (corresponding author).