Analysis-Oriented Stress–Strain Model for Prestressed FRP-Confined Circular Concrete

To develop an analysis-oriented stress–strain model for prestressed fiber-reinforced polymer (FRP)-confined circular concrete, the path-dependent responses of prestressed FRP-confined concrete and actively confined concrete were systematically investigated. Existing experimental data were used to examine the applicability of the stress-path independence and strain-path independence assumptions under different prestressing methods. The filament winding method generally satisfies the stress-path independence assumption, with relative errors in axial stress mostly within 10%, whereas direct application of the actively confined concrete model to expansive-concrete method specimens results in errors close to 20%. After accounting for the initial confinement effect, these errors are generally reduced to within 10%. Strain-path comparisons further show that the prestress-induced initial lateral strain should be considered; after removing this initial strain component, the lateral strain–axial strain relationship shows strong consistency with that of actively confined concrete. Accordingly, the peak stress, peak strain, and lateral strain–axial strain relationship were modified, and a strain-controlled incremental calculation procedure was established to generate the complete stress–strain response. Validation against compiled published experimental data yielded an R² of 0.931 and a MAPE of 8.88% for compressive-strength prediction, while the predicted axial stress–strain and lateral dilation responses also showed reasonable agreement with the experimental results. The proposed model can therefore support nonlinear analysis over the complete loading range and quantitative assessment of strength and deformation for different prestress levels and FRP confinement parameters within the validated range.