A Macromechanical Constitutive Model for Rebar Buckling

Abstract

Rebar buckling and fracture have been experimentally observed to cause significant degradation of the mechanical properties of reinforced concrete (RC) elements and should be accounted for in the analysis of RC structures. While data on the material properties of steel rebar are widely available, test data on rebar buckling remain scarce. This paper proposes a macromechanical model capable of predicting rebar buckling responses solely on the basis of steel material properties and the rebar geometry, even when rebar buckling experimental data are not available. This is achieved by computationally building the uniaxial stress-strain constitutive response at each analysis step through the equilibrium in the deformed configuration of the buckled rebar and through the cross-sectional constitutive response. The equilibrium in the deformed configuration is treated in a manner consistent with the corotational formulation, while the cross-sectional constitutive response is built through integration of a uniaxial damage plasticity model over the cross-section area. Rebar buckling is triggered by an initial imperfection, while low-cycle fatigue effects are reproduced through the uniaxial damage plasticity steel material model, without the need for cycle-counting algorithms. The proposed model is translated to a computer code, calibrated to a set of experimental data, validated to separate test data, and subsequently used in the analysis of an experimentally studied RC column that experienced rebar buckling under cyclic loading. Using the proposed model, the analysis captured the response of the RC column and the experimentally observed strength deterioration due to rebar buckling.