Constitutive model for reinforcing bars including bar buckling and low-cycle fatigue

In this paper, a path-dependent cyclic stress–strain model for reinforcing bars that incorporates the effect of bar buckling, low-cycle fatigue damage and loading history is proposed. A comprehensive experimental campaign is conducted to investigate the hysteretic behaviour of buckling-prone bars and the test results are used to develop and calibrate cyclic average stress versus average strain relationship for reinforcing bars. The parameters considered in this study include the slenderness ratio of reinforcing bars, grade of reinforcing bars and the loading history. Through a detailed analysis of test results, the effect of geometrical nonlinearity on the hysteretic response of the bar is evaluated and an analytical model simulating the effect of buckling on hysteretic response of the bar is developed. The cyclic model proposed herein captures the post-buckling stress deterioration, reduction of compressive stresses due to residual tensile strains (i.e. plastic strains), and reduction of unloading and reloading stiffnesses due to buckling and low-cycle fatigue damage in reinforcing bars. Comparison between experimental and analytical results shows that the proposed model can reliably predict the cyclic response of reinforcing bars including the effects of buckling and low-cycle fatigue.