Cyclic behavior and shear strength of exterior reinforced concrete beam-column joints with inclined columns

Abstract

The adoption of inclined columns results in inclined beam-column joints (BCJs). Although the behavior of regular BCJs have been widely investigated, researches on the cyclic behavior and shear strength of inclined BCJs are limited, and further investigations are required to ensure seismic safety of the frames adopting inclined columns. In this work, cyclic behavior of inclined BCJs was first experimentally studied by testing 3 exterior BCJ specimens. After that, a finite element model was developed and validated by the experimental results. The model was subsequently used for parametric study to reveal the effects of key parameters on the joint shear strength. In the end, a theoretical model based on the softened strut and tie model was proposed to estimate the joint shear strength of inclined BCJs. Results showed that the inclination caused an initial joint shear force under column axial load, leading to different joint behavior in positive and negative loading directions. The joint shear strength was increased in the inclination direction but declined in the other direction, while the ductility showed an opposite trend. Meanwhile, regardless of the inclination direction, energy dissipation and equivalent viscous damping of BCJs were reduced and stiffness degradation was slowed. The parametric study revealed that the inclination effect was amplified with higher inclinations. The overall joint shear strength can be effectively enhanced by adopting higher concrete strength and column axial load. Increasing the joint stirrup ratio was also beneficial for the shear strength, but its efficiency was relatively lower. Based on the comparison of the predicted joint shear strengths and those from experimental and numerical programs, it was proved that the modified strut and tie model was advantageous over the formulas in GB 50010 in capturing the shear strengths. This work contributes to understanding the cyclic behavior and shear strength of inclined BCJs to improve seismic safety of frames adopting inclined columns.