99-0013 Critical Seismic Issues for Existing Steel Bridges P.Ritchie, N. Kauhl and J. Kulicki 1999 Modjeski & Masters, Inc. 132 PB2000-101697 25 The overall objective of this task was to examine, evaluate, and improve design methodologies for hinge restrainers currently in use by Caltrans and AASHTO. This report addresses hinge restrainers and seat width design for multiple-frame bridges. The authors developed a numerical model to investigate the response of these bridges when subjected to earthquake ground motion, focusing on the longitudinal reponse of the frames and the hinges. They examined the effects of various dynamic characteristics on the inelastic earthquake reponse of these types of bridges. On the basis of this analysis, a new, greatly simplified design procedure for hinge restrainers and hinge seat widths was developed and verified by a series of parameter studies and case studies. Highway bridges. Hinges. Fasteners. Mathematical models. Ductility.