Improved Nonlinear Cyclic Stress–Strain Model for Reinforcing Bars Including Buckling Effect and Experimental Verification

Buckling is an important nonlinear behavior of steel reinforcing bars subjected to repeated compression and tension strain reversals, which significantly affects the overall cyclic behavior of reinforced concrete (RC) elements and impairs their load-carrying and energy-dissipation capacities during strong earthquakes. The accuracy of numerical assessment of the seismic performance of RC elements can be much improved if the buckling effect is effectively included in the stress–strain model of reinforcing bars. In this paper, modified Gomes–Appleton cyclic steel stress–strain relationship intended for improved accuracy is presented, which is suitable for inclusion in programs based on Opensees platform for the nonlinear analysis of RC elements. The modification is developed to improve the simulation accuracy of the inelastic buckling stress–strain path by a simplified model based on the equilibrium of a plastic mechanism of buckled bar consisting of four plastic hinges. Then an adjustment coefficient is introduced to further modify the developed buckled bar stress–strain model. A comparison of the numerical simulated results with experimental results of 36 steel bars subjected to reversed tension-compression loading is performed to verify the accuracy and effectiveness of the proposed model.