Numerical analysis on seismic behavior of RC beam-column joints with headed diagonal bars and the influence of reinforcement detailing

This paper presents the results of numerical analysis on reinforced concrete interior beam-column joints with headed diagonal bars, utilizing 3D nonlinear finite element analysis procedures. A fracture-plastic model incorporating a smeared fixed crack approach and crack/crush band model was employed to simulate the complex behavior of these interior joints under reversed cyclic loading. Four interior beam-column joints from the literature were modeled and validated, and their detailed seismic performance was further evaluated. In addition, new parametric studies were undertaken to explore the influence of various reinforcement details on the joints' seismic performance and cracking behavior. Based on the results presented, it was shown that the utilization of headed diagonal bars led to an improved load capacity and energy dissipation. The extent of joint deterioration in specimens with headed diagonal bars, however, varied depending on the quantity of joint stirrups provided. In addition, a successful plastic hinge relocation away from the beam-column interface was obtained in the simulated models, consistent with experimental observations. Furthermore, the results from the parametric studies revealed that removing joint stirrups led to strength degradation and shear failure modes, while increasing beam longitudinal bar diameter enhanced load capacity but also strength degradation, prompting flexure-shear dominant failure modes. Moreover, the variation in bond properties between the diagonal and straight segments of headed bars was shown to have little impact on overall seismic performance, although it was important to note that joint cracks were more uniformly distributed with bonded properties, leading to more stable strength degradation.