Assessment and design of restrained reinforced concrete beams subjected to hysteresis elongation effects

In reinforced concrete frame structures, beams subjected to cyclic loading exhibit hysteresis elongation, which is typically restrained by adjacent members. This restraint induces axial compression in the beams, leading to overstrength and increased force demands on joints and columns. However, due to the lack of predictive models for this restraint-induced axial compression, current seismic design procedures do not explicitly account for its potentially adverse effects. To address this gap, a detailed modeling approach incorporating bond-slip behavior is firstly validated against available experimental results to ascertain its ability to capture elongation restraint effects. Following validation, 312 nonlinear cyclic simulations are conducted to assess the influence of geometric, detailing, and material parameters on the response across a wide range of axial restraint stiffnesses. The results reveal that, while the restraint-induced axial compression level is affected by several parameters, it is primarily governed by the longitudinal reinforcement ratio and the concrete compressive strength. Based on these findings, a simple predictive model is developed to estimate the induced compression level, and its accuracy is verified against the numerical and experimental results. Using this model, a design and detailing procedure is suggested for beam elements, with due account for the restraint-induced axial compression. The application of the procedure to representative beam-column subassemblies shows its effectiveness in mitigating beam overstrength and limiting excessive joint shear demands. The study offers a fundamental quantitative approach for addressing the adverse consequences of restrained beam elongation under cyclic loading in order to enhance the seismic performance of reinforced concrete frame structures. • A refined modeling procedure is used to assess elongation restraint effects under cyclic loads. • The numerical modeling approach is validated in detail against experimental results. • Key parameters influencing elongation restraint effects are identified and discussed. • A simplified prediction model is proposed to estimate restraint-induced axial compression. • A design method is developed to account for restraint-induced axial compression.