1. Dept. of Civil and Environmental Engineering, Univ. of Connecticut, 261 Glenbrook Road, Unit 2037, Storrs, CT 06269-2037. E-mail: acb@engr.uconn.edu
2. Ralph M. Parsons Laboratory, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, 48-321, 15 Vassar Street, Cambridge, MA 02139.