Behavior of RC interior beam-to-column joints with FRP-strengthened beam web openings under cyclic loading

Abstract

Despite the widespread adaption of the design criterion of strong column and weak beam (SCWB) in reinforced concrete (RC) frames, many existing RC frames cannot meet the design requirements of SCWB. Therefore, a novel beam opening (BO) technique for retrofitting RC frames that violate the SCWB design philosophy was proposed. The BO technique involves the creation of a web opening at the beam end near the joint to weaken its flexural capacity. In order to offset the reduced shear capacity due to the web opening, a fiber-reinforced polymer (FRP) shear strengthening system also needs to be applied around the opening. However, all previous relevant studies have been focused on the behavior of RC beams with FRP-strengthened web openings. To further verify the effectiveness of this technique, this study conducted experimental and numerical evaluations of RC joints with beam web openings under cyclic loading. Three full-scale RC interior beam-to-column joints were fabricated and tested under lateral cyclic loading and the results were evaluated in terms of failure modes, hysteresis behavior, ductility, energy dissipation, and stiffness degradation. The test results indicated that the inclusion of beam web openings successfully changed the failure mode of the joint from column-end failure to beam-end failure. Subsequently, finite element models of the three test specimens were established and the simulation results agreed well with the test results.