Update on Analytical and Experimental Research on Bridge Restrainers

Bridge restrainers are used to inhibit relative displacements, prevent unseating of the bridge, and transfer longitudinal seismic forces between adjacent spans at in-span hinges or at hinges between simply supported spans. They have proved to be very effective in earthquakes such as the ones in 1987 at Whittier Narrows, in 1989 at Loma Prieta, and in 1994 at Northridge. Two procedures are currently used to design restrainers in the United States. At the same time, various analytical studies have investigated the dynamic performance of restrainers in the cases of both simply supported and in-span hinges, and several new restrainer design methods have been developed. These studies have shown that although the currently used design methods are conservative in most cases, they neglect many parameters that are important for the response of hinges. Furthermore, new large-scale experimental studies either have been performed or are in the development stage. These studies are expected to enhance the understanding of the complicated phenomenon of hinge response to earthquake excitations. Most of the currently used design methods are presented, and the most recent analytical and experimental studies are discussed.