To investigate the shear-resisting behavior of cap beams in RC rigid frame bridges under seismic loading, experiments were conducted using two seismically-strengthened pier specimens. The hoop tie ratio was used as the parameter. According to the experiments, the beams of the specimens suffered shear damage after plastic hinges were formed at four positions. It was found that the hoop tie ratio of the beam does not affect the maximum strength of the beam, but significantly affects its deformation capacity. The FEM analysis showed that strain of hoop ties increased as the deformation of the beam increased, which suggests that shear damage to the beam was caused by the decrease of shear resisting capacity of the concrete in the beam.