Numerical Investigation of Axial Compression Behavior of FRP-confined RC Columns Based on a Damage-plasticity Model

To further investigate the mechanisms and parametric influences of Fiber-Reinforced Polymer (FRP) confinement on the axial compressive capacity and ductility of Reinforced Concrete (RC) columns, this study employs the Ferrotto damage plasticity model to develop a three-dimensional finite element model. The model was calibrated and validated using the full-scale specimens K1/K3 from Matthys’ experiments, followed by a parametric analysis examining the effects of FRP layer number and concrete strength. The results indicate that the model accurately replicates the experimental stress-strain curves. FRP confinement leads to a more uniform distribution of lateral and axial stresses with higher magnitude in the concrete core, while reducing the stirrup stress at the mid-height of the column by approximately 50% compared to unconfined columns. As the number of FRP layers increases from 2 to 4 and then 6, the load-bearing capacity initially rises nearly linearly before the growth rate gradually slows, with ductility consistently improving. Higher concrete strength enhances the bearing capacity, but the relative increase diminishes progressively; meanwhile, the ultimate compressive strain decreases as concrete strength rises. The proposed model, which requires no user subroutines and balances convergence with accuracy, can serve as an effective tool for the analysis and design of FRP-confined RC columns under axial compression. Moreover, it provides detailed stress-strain field information that contributes to a deeper understanding of the mechanical behavior of FRP-confined concrete columns.