Strut-and-tie modelling for the analysis and design of RC beam-column joints

Beam-column joints have been recognised as one of the potentially weaker elements of reinforced concrete moment-resisting frame structures when subjected to seismic lateral loading. Prior earthquake reconnoitring reported the notable damage that can develop from inappropriate beam-column joint design. Design formulae available in building codes and literature differ considerably in functional form, do not consider all of the key variables that affect the joint response, and broadly predict quite different values of shear strength from one another. A mathematical model based on the strut-and-tie model is developed to estimate the shear strength of exterior and interior reinforced concrete beam-column joints. The proposed model leads to an explicit single closed-form expression for computing the shear strength and accounts for the shear stress contributions provided by the diagonal concrete strut and the shear reinforcement (including both joint hoops and column intermediate bars), while considering those variables that significantly affect the behaviour of such joints. Model parameters were calibrated using the experimental results of 454 exterior and interior joints available in the literature. When compared to a number of predictive expressions for the shear strength of joints, the proposed model provides the best fit with the measured shear strength. Further, a set of simple code-oriented design formulae, with conservative predictions, is proposed to facilitate practical engineering design.