Unified model for evaluating ultimate strain of FRP confined concrete based on energy method

•Derivation of ultimate strain of FRP confined concrete columns with an energy method.•Unified ultimate strain model that is applicable to circular, square and rectangular columns.•Model applicable to both concentric and eccentric loading.•Improved accuracy compared with existing models.

An energy balance approach is adopted to develop the model for calculating the ultimate strain of fiber-reinforced polymer (FRP) confined concrete columns in this work. The proposed model can be used to predict the ultimate strain of columns under both concentric and eccentric loading. In the meantime, it makes use of a unified form so that it can be applied to different shapes of columns. A database that includes a large number of updated test results is used to evaluate the model parameters and coefficients. Compared with other existing models reported in extant literature, the proposed model exhibits a better performance.