Analytical investigation of the structural behavior of reinforced concrete columns wrapped with fiber polymer

In this study, the structural behavior of reinforced concrete columns externally confined with fiber-reinforced polymer (FRP) composites is analytically investigated. FRP confinement is widely recognized as an effective alternative strengthening technique to conventional methods, aiming to enhance both the strength and ductility of reinforced concrete columns. Traditionally, transverse reinforcement (TSR), externally bonded reinforcement plates, and steel or reinforced concrete jacketing have been employed to improve the strength and ductility of concrete members. Compared to these conventional techniques, FRP confinement offers several advantages, including high tensile strength and stiffness, lightweight properties, corrosion resistance, ease of installation, and efficient confinement performance. The mechanical properties of FRP confinement positively affect the behavior of reinforced concrete structures by increasing the compressive strength and strain capacity of concrete. Analytical calculations were conducted within the scope of this study using the ABAQUS/CAE software. Finite element modeling (FEM) and analytical approaches were employed to investigate the structural behavior of reinforced concrete columns strengthened with FRP under various confinement and loading conditions. The results obtained from the finite element models were verified by comparison with analytical and experimental data available in the literature. In this context, circular and rectangular reinforced concrete columns with different confinement methods including full FRP wrapping, TSR confinement, partial FRP arrangements, and combined FRP–TSR systems were modeled under axial and eccentric loading conditions. For each case, the effects of FRP and TSR volume ratios, the aspect ratio of rectangular sections, corner radius, unconfined concrete strength, and other critical parameters on confinement effectiveness were evaluated. The analysis results demonstrated that FRP confinement significantly enhances both the load-carrying capacity and ductility of circular and rectangular reinforced concrete columns under axial and eccentric loading conditions. The combined confinement method using FRP and TSR provides greater effectiveness and superior performance compared to the methods applied individually. The findings indicate that circular columns achieve higher confinement efficiency due to their geometric advantages, whereas rectangular columns exhibit lower efficiency because of the non-uniform distribution of lateral confining pressure around the section. Partial FRP wrapping configurations were generally more effective than full confinement, particularly for eccentrically loaded columns, which experience irregular distributions of bending moments along the column height. However, the effectiveness of partial confinement depends directly on the position and arrangement of the FRP strips, and its efficiency can exceed that of full confinement when equivalent volumetric ratios are used. For eccentrically loaded confined columns, P–M interaction diagrams developed through finite element modeling and analytical integration methods were employed to evaluate the effectiveness of FRP confinement. The results strongly indicate that FRP confinement provides a high level of efficiency in enhancing the structural behavior of reinforced concrete columns, highlighting its potential as a practical, effective, and applicable strengthening technique.