Research on seismic performance of RC exterior beam-column joints considering bond degradation mechanism based on a novel combined spring element

To accurately evaluate the bond degradation mechanism between reinforcements and concrete under cyclic loading, finite element models for RC exterior beam-column joints incorporating bond degradation characteristics were developed in this study. A novel combined spring element was introduced using the finite element program ANSYS to simulate the bond degradation behavior, along with a calibration method for the force-displacement (F-D) curve of the combined spring elements. Additionally, a prediction model for the bond-slip constitutive relationship under cyclic loading was proposed based on damage theory. The validity of the combined spring elements and the bond-slip prediction model was verified through comparisons between simulation and experimental results. The Voce-Chaboche combined hardening model was employed to define the cyclic constitutive behavior of reinforcements. Simulated skeleton curves, hysteresis curves, stiffness degradation curves, and stress distributions were compared with experimental data. The results revealed that the Voce-Chaboche combined hardening model accurately captures the hysteretic behavior of reinforcements. The combined spring elements effectively simulate the bond degradation between reinforcements and concrete under cyclic loading. Furthermore, the development of plastic hinges during cyclic loading results in plastic elongation of the beam, adversely affecting the columns in the joints. The simulated hysteresis curves exhibit a pronounced pinching effect, with trends in strength and stiffness degradation closely aligning with experimental results. The established finite element modeling approach provides a theoretical and technical framework for accurately simulating the bond degradation mechanism of beam-column joints.