Inelastic buckling of corrosion damaged reinforcing bars

Abstract: In the seismic design and assessment of reinforced concrete structures in earthquake zones buckling of longitudinal reinforcement in plastic hinge regions is an important limit state that needs to be considered. If the structure is located in an environmentally aggressive area, it is also subject to material deterioration over its service life. Corrosion of reinforcement is the most common type of deterioration of Reinforced Concrete (RC) structures and bridges. In this research the nonlinear stress-strain behaviour of corroded reinforcing bars has been investigated by extensive experimental testing. The effect of different corrosion levels on the tension and compression behaviour of bars with different slenderness ratios is presented. The results of this study show that a corrosion level above 15% mass loss significantly affects the ductility and plastic deformation of reinforcement in tension and that corrosion changes the buckling collapse mechanism of the bars in compression. The results of buckling tests show that 10% mass loss produces about a 20% reduction in the buckling capacity of corroded bars. The results also show that the distribution of corrosion pits along the length of corroded bars is the most important parameter affecting the stress-strain response in both tension and compression. Furthermore, a constitutive material model to predict the post-yield buckling behaviour of high-strength steel without a yield plateau is also developed. The proposed analytical model is based on Dhakal-Maekawa buckling model. The analytical model has been validated against experimental tests on uncorroded and corroded bars. The results of this corrosion extended buckling model show a good agreement with the physical testing.

Keywords: Reinforcing steel; Corrosion; Inelastic buckling; Post-buckling; Stress-strain relationship; Constitutive models; Nonlinear analysis

Nonlinear cyclic behaviour of corrosion damaged reinforcing bars with the effect of inelastic buckling

Abstract: Corrosion of reinforcing bars is the most common reason for the premature deterioration of reinforced concrete structures and bridges in a chloride laden environment. There are large numbers of existing reinforced concrete bridges in earthquake prone regions that are suffering from corrosion. Therefore, in this research, the effect of corrosion on cyclic response of reinforcing bars is investigated experimentally. A total of 40 corroded reinforcing bars with varying mass loss and slenderness ratios have been tested. The effect of corrosion on the buckling behaviour of bars in compression, their fracture in tension and their hysteresis response is investigated. Furthermore, an analytical model is proposed to describe the low-cycle high amplitude fatigue degradation of corroded bars. The results of the experimental investigation show that corrosion has a significant influence on the buckling behaviour of corroded bars in compression and also changes their hysteresis response. In some cases the localised corrosion caused fracture of corroded bars in tension after a significant buckling episode in the previous compression cycle. The proposed corrosion extended low-cycle fatigue and inelastic buckling models have been incorporated into the existing material models and simulated computationally for the whole cyclic loops.  A good qualitative fit is observed between the computational simulation and the experimental response when the corrosion is relatively uniform along the bar. However, some disagreements were found between the computational and experimental responses in cases where the corroded bars had severe, localised, pitting corrosion. It was observed that the most important parameter governing the nonlinear cyclic response is the distribution of localised pitting corrosion along the length of the corroded bars. 

Keywords: Reinforcing steel bars; Corrosion; Inelastic buckling; Stress-strain relations; Nonlinear analysis; Cyclic behaviour; Low-cycle high amplitude fatigue

Finite element modelling of corroded reinforcing bars

Abstract: An optical surface measurement technique was used to characterise three-dimensional corrosion pattern of reinforcing bars subjected to accelerated corrosion. After the optical measurement process was performed, the corroded bar specimens were tested under monotonic and cyclic axial loading. The optical measurement data were used to develop a 3D micro-fibre finite element model developed for simulation of the physical testing and parametric study of the influence of corrosion pattern on stress-strain response of corroded bars. It was observed that the irregular cross sectional shape of pitted sections has a significant influence on the inelastic buckling and nonlinear cyclic response. 

Keywords: Reinforcing steel; Corrosion; Inelastic buckling; Stress-strain relations; Nonlinear analysis; Cyclic behaviour; Low-cycle fatigue

Development of an advanced phenomenologycal material model for reinforcing bars including inelastic buckling, fatigue degradation and corrosion damage

Abstract: A new phenomenological hysteretic model for reinforcing bars with and without corrosion damage is developed. The model simulates buckling of reinforcement, deterioration in post-buckling compressive strength due to strain history and the impact of low-cycle fatigue on tension response. The basic model, for uncorroded reinforcing bars, is calibrated using data from numerical simulations and corrosion damage parameters are calibrated using experimental data. The model is evaluated using a comprehensive experimental data set, and the results show that the model is in a good agreement with the data.   

Keywords: Reinforcing steel; Corrosion; Inelastic buckling; Hysteretic model; Constitutive modelling; Low-cycle fatigue