1. MacLean Professor of Engineering, Dartmouth College, Hanover NH 03755.
2. Professor and Chair, Dept. of Civil and Environmental Engineering, Univ. of Wisconsin-Madison, 2205 Engineering Hall, 1415 Engineering Dr., Madison, WI 53706 (corresponding author).
3. Professor and Chair, Dept. of Civil and Environmental Engineering, Bucknell Univ., Lewisburg, PA 17837.
4. Associate Professor, Dept. of Civil Engineering, Rose-Hulman Institute of Technology, Terre Haute, IN 47803.