1. INSA/GPI/LIPE, Complexe Scientifique de Rangueil, Toulouse, F-31077 Toulouse Cedex 4, France (E-mail: benaim@insa-tlse.fr)
2. Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive SE, 122 Civ. E., Minneapolis, MN 55455-0220, USA (E-mail: semme001@maroon.tc.umn.edu)