Stiffness-based stress–strain model of FRP-confined high-strength and ultra-high strength concrete column with various corner radii

Abstract

This study introduces a unified design-oriented stress–strain model tailored for fiber-reinforced polymer (FRP)-confined high-strength concrete (HSC) with diverse cross-sectional shapes. The proposed stress–strain model incorporates more suitable mathematical forms, incorporating post-peak axial stiffnesses as crucial parameters, thereby enabling the model to accurately capture the three types of post-peak stress–strain behavior observed in FRP-confined HSC: strain-hardening, strain softening, and strain softening recovering to strain hardening. This variation in post-peak axial stiffness arises due to insufficient FRP confinement at the initial peak strength point, as well as changes in the confinement stiffness ratio stemming from the altered dilation behavior of FRP-confined HSC during the post-peak stage. To address the nonuniform effects of FRP confinement, the concept of effective confinement rigidity was defined, unifying the behavior of FRP-confined circular and square HSC. Additionally, the model incorporates the ultimate condition and the characteristic point on the post-peak branch, representing the change in FRP confinement stiffness, to establish the stress–strain model for FRP-confined HSC. The model parameters were evaluated using available experimental results, and the stress–strain curves derived from the proposed model were compared with existing models in the literature, revealing the proposed model's accuracy and rationality.