1. Winzler and Kelly Consulting Engineers, 633 Third St., Eureka, CA 95501.
2. Professor, Dept. of Civil and Environmental Engineering, 18 Marston Hall 12A, Box 35205, Univ. of Massachusetts, Amherst, MA 01003-5205 (corresponding author).
3. Dept. of Mechanical and Industrial Engineering, Univ. of Massachusetts, Amherst, MA 01003-5205.
4. Dept. of Civil Environmental Engineering, 18 Marston Hall 12A, Box 35205, Univ. of Massachusetts, Amherst, MA 01003-5205.