Energy balance method for modeling ultimate strain of fiber-reinforced polymer-repaired concrete

The energy balance method has been widely used in the extant literature to derive the ultimate axial strain of conventional confined concrete columns. However, researchers noted that this method yields unrealistic results compared to experimental data when it is applied to fiber-reinforced polymer (FRP) confined concrete columns. Therefore, it is deemed that the existing ultimate strain model based on the energy method cannot be directly applied to FRP-repaired concrete. With this model shortcoming in mind and through a theoretical analysis with proper calibration, the current study extended the energy balance approach to develop a generalized model to determine the ultimate strain of FRP repaired concrete columns. This proposed new model can be used to predict the ultimate strain of repaired columns under both concentric and eccentric loadings. Because this model is established in a unified form without any restrictions to the cross-sectional geometry, it is applicable to different shapes of repaired columns. On the other hand, although the energy balance method is unconservative for heavily damaged concrete, it exhibits a better performance with respect to the existing models when compared with the test result.