Deformation Capacity Analysis of Large Rupture Strain FRP-Confined Concrete with Local Stress–Strain Effects

Ultimate deformation capacity is a key indicator for assessing the failure state of structural members, marking the final failure of concrete. This study investigates the deformation behavior of large rupture strain fiber-reinforced polymer (LRS-FRP)–confined concrete columns under axial compression, with a particular focus on the role of localized stress–strain responses in governing global structural deformation. Eighteen polyethylene terephthalate FRP-confined concrete specimens with varying corner radii and height-to-width ratios were tested to explore the influence of confinement efficiency on the stress–strain curves. The resulting stress–strain curves were categorized into two types: peak enhancement and ultimate enhancement curves, each associated with distinct deformation mechanisms. Axial strain distributions indicate that the extent of postpeak strain enhancement determines whether local damage remains confined or propagates, thereby governing the overall deformation characteristics of slender columns. Building upon these insights, a unified stress–strain model was developed that integrates both new data and validated literature results. The proposed model accurately predicts the ultimate strain of LRS-FRP-confined concrete with various cross-sectional shapes and slenderness ratios; by explicitly accounting for the influence of local damage propagation through the classification of stress–strain behavior, it outperforms existing models in predicting the ultimate deformation of slender columns. These findings provide a robust framework for designing LRS-FRP-confined concrete members, enabling more reliable assessment of failure modes and deformation capacities under extreme loading conditions.