Structural behavior of RC columns retrofitted with FRP under axial load

The strengthening of reinforced concrete columns using fiber-reinforced polymer (FRP) composites has garnered significant attention in recent years due to its numerous advantages.RC columns primarily support axial compression loads and often require strengthening to improve their axial strength and ductility.This research investigates the analytical structural axial behavior of rectangular RC columns retrofitted externally with FRP, internally strengthened with transverse steel reinforcement (TSR), or strengthened using a combination of FRP and TSR techniques, applied externally and internally, respectively.The research also aims to identify precise stress-strain models that accurately represent the mechanical behavior of rectangular RC columns which experience irregular stress variations due to their geometry, in three different confinement configurations: FRP, TSR, and combined confinement of FRP and TSR, under pure axial compression loads.Furthermore, five rectangular and square cross-sectional RC columns with various dimensions and confinement configurations have been analyzed using three confinement methods under pure axial compressive load, and all influential parameters were investigated analytically with the proposed models.The results show that the stress-strain relationships obtained from the suggested models are in good agreement with experimental data taken from the literature and previous studies.Based on the findings, combined confinement reinforcement using FRP and TSR demonstrates greater benefits than individual methods in improving the structural axial behavior of rectangular RC columns under axial loads, making this technique particularly effective for enhancing axial load-bearing capacity and ductility.