Design of seismic cable hinge restrainers for bridges

The collapse of bridges due to unseating at intermediate (in-span) hinges during recent earthquakes emphasizes the need to provide an adequate number of restrainers to limit the relative displacement between frames in a bridge with inadequate hinge seat width. Current restrainer design procedures do not account for the factors affecting the earthquake response of multiple-frame bridges. A parameter study indicates that maximum hinge displacement is a function of the frame period ratio, frame ductility, and the characteristics of the ground motion. A new design procedure for hinge restrainers, based on a linearized model, is developed. The procedure accounts for the dynamic characteristics out-of-phase motion of adjacent bridge frames. Inelastic behavior of frames is accounted for by using the substitute structure method. Parameter studies and case studies using over 26 different mound motion records show that the new procedure limits and the relative hinge displacement to a designer-specified value for a wide range of bridges.