Post-earthquake reconnaissance confirmed that the high vulnerability of non-seismically detailed RC frame structures could be related to shear failure in the core of the beam–column joints which might cause the collapse of the structure. The main focus was given on developing a simplified numerical model to simulate RC beam–column joints collapse based on theoretical formulations and experimental observations. For this, a joint model has been proposed so that nonlinearities in the joint core were considered by two diagonal axial springs. According to the principal stress approach, a more refined calibration of principle tensile stress versus joint rotation relation was developed to calculate the characteristics of these springs. In the model, the effects of the main factors influencing the mechanical behavior of RC joints i.e. column intermediate bars, joint aspect ratio, joint shear reinforcements, type of beam bar anchorage, etc. were considered. To verify the simplified numerical model, it was vastly applied to experimental specimens available in the literature. Results revealed that the model was capable of estimating inelastic response of RC joints with reasonable precision. Furthermore, assuming the joint core to behave as a rigid body, even for joints reinforced by shear reinforcements might bring about non-conservative predictions in terms of strength and ductility capacities. Based on a parametric study, it was also concluded that the effectiveness of the influential factors of RC beam–column joints is noticeably a function of the level of the axial load applied on the column. Using experimentally computed factors and simple procedure to calculate joint characteristics could make the model properly suitable for practical applications.
