DESIGN AND EXPERIMENTAL INVESTIGATION OF A NEW TYPE SLIDING RETAINER AND ITS EFFICACY IN SEISMIC FORTIFICATION

The regular retainer is ineffectual in seismic fortification for girder bridges in China. A new type aseismic retainer is proposed to achieve the improvement with respect to two performance indices: displacement control and force transfer. Quasi-static experiments are designed to comparatively investigate the seismic performance of the new retainer and the regular retainer. Simplified hysteretic analytical models are established for the two types of retainers respectively based on the recorded force-deformation relationship curves, and are used in comparative research of seismic fortification for a real bridge. The results show that the new retainer fails due to large-displacement sliding shearing on the top surface of the cap beam while the cap beam remains intact, which is favorable for post-earthquake repair or replacement. Compared with the regular retainer subjected to diagonally brittle shear failure, the ultimate deformation capacity and deformation ductility of the new retainer are significantly large. Furthermore, the new retainer is more efficient than the regular retainer in controlling the displacement of girders and the shear deformation of elastomeric bearings. Under small to moderate earthquakes, the new retainer has less effect on the seismic response of pier; but under large earthquakes, the new retainer, due to its large deformation ductility, is able to protect the elastomeric bearings and to prevent the unseating of girders when a larger transverse displacement response occurs.