1. Assistant Professor, Dept. of Civil Engineering, Purdue Univ., 550 Stadium Mall Dr., Civil Engineering Building, Room 1235, West Lafayette, IN 47906 (corresponding author). E-mail: jvs@purdue.edu
2. Professor, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307.
3. Principal Research Associate, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307.
4. Group Leader, Lincoln Laboratory, 244 Wood St., Lexington, MA 02123.
5. Senior Associate, Haft, Harrison, and Wolfson, Inc., Boston, MA; formerly, Lincoln Laboratory, 244 Wood St., Lexington, MA 02123.