| After repeated earthquake events, it has been addressed and emphasized that beam-column connections are critical regions in multi-story reinforced concrete frames. High inelastic actions are reported to concentrate at the joint regions when the building is excited by a severe earthquake. Despite the significant number of researches conducted on beam-column connections, design recommendations of different codes conflict with each other. In addition, the current recommendations do not account for new materials such as steel fibers or when high strength concrete is used which independently may reduce the steel congestion in the joint. Furthermore, recent earthquake records indicate the disastrous effects when high vertical ground motion co-exists with high horizontal excitation. This fact has been emphasized by the recent Northridge earthquake of January 17, 1994. The present investigation is devoted to study the seismic shear capacity of interior beam-column joints under the influence of certain key parameters. The parameters are the column load to reflect the influence of the vertical excitation, the use of steel fibers as main shear reinforcement in the joint, the amount of conventional joint shear reinforcement, and the use of high strength concrete. A review of the available research work was undertaken and a comparison between various codes was conducted. Ten interior beam-column connections were tested in this experimental program. A new column-load device was designed and used to apply the required level of tensile or compressive axial load on the moving column. All specimens failed due to the predefined shear mode of failure. An analytical model was developed to study the shear behavior of the joint core. The model satisfies compatibility of strains and equilibrium of stresses in an average sense. The concrete contribution and the truss action are included in the model formulation. The model predicts the dilation of the joint core and estimates the joint shear strength with sufficient accuracy. Practical conclusions and design guidelines are drawn based on the present experimental and analytical study. |
