1. Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of California, Irvine, CA 92697-2175.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Irvine, CA 92697-2175.
3. Air Force Research Laboratory, RQRP Branch, 10 East Saturn Blvd., Edwards Air Force Base, CA 93524 (corresponding author).