Effect of axial compression ratio on dynamic mechanical properties of RC beam–column joints

The dynamic mechanical properties of 15 interior beam–column joint specimens subjected to various axial compression ratios are studied. Failure patterns of beam–column joints and development of cracks are predicted by a softened strut-and-tie model and binomial logistic regression model. According to the Coulomb failure criterion and Mohr's circle theory, a model to calculate the shear strength of concrete is derived under the shear compression state. In terms of the effects of different strain rates and axial compression ratios, the carrying capacity, stiffness and carrying capacity degradation, energy dissipation, displacement ductility, bond slip and failure mode of beam–column joints are discussed in detail. Finally, different building codes are selected to compare the results. It is found to be unsafe to substitute the dynamic strengths of concrete and reinforcement bar directly into the quasi-static design formulas to calculate the shear carrying capacity of the beam–column joint, because the shear carrying capacity of the joint is overestimated. To make a more reasonable assessment of the effect of strain rate and axial compression ratio, an empirical equation to predict the dynamic increase factor of horizontal shear carrying capacity of beam–column joints under different axial compression ratios and strain rates is proposed through multiple linear regression analysis.