AbstractExtensive experimental and theoretical studies of large rupture strain (LRS) fiber-reinforced polymer (FRP)-confined concrete columns have been conducted based on small-scale columns, mostly with a diameter of 150 mm. This paper presents the first-ever study on the axial performance of LRS polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) FRP-confined large-scale concrete columns. Twenty PET FRP-confined circular concrete columns and 20 PEN FRP-confined square concrete columns were loaded concentrically. The cross-sectional diameter or side length ranged from 100 to 400 mm. The effects of specimen size and FRP volume ratio on the failure mode, axial stress–strain relationship, and dilation behavior were investigated. The load-carrying capacity and ductility of LRS FRP-confined concrete increased with an increase of the FRP volume ratio. As the specimen size increased, the confinement efficiency of the FRP decreased, resulting in a lower strength enhancement. The accuracy of existing size-dependent strength models was also evaluated using the residual error. Furthermore, a modified size-dependent model for LRS FRP-confined circular/square concrete columns was developed, which was shown to have a more satisfactory performance than the existing models. The proposed model can serve as a basic model for the seismic analysis of strengthened reinforced concrete (RC) columns with LRS FRP, with the possible size effect duly accounted.