Axial compression behavior of FRP reinforced concrete columns based on database analysis and finite element validation

Abstract

This study presents a comprehensive analytical evaluation of the axial compression behavior of fiber-reinforced polymer–reinforced concrete (FRP-RC) columns. The investigation focuses on the combined effects of transverse confinement, FRP material type, column geometry, and concrete compressive strength, while explicitly considering both short and slender column configurations to evaluate the influence of geometric slenderness on structural response. The compiled experimental database covers concrete strengths ranging from approximately 10 to 90 MPa and includes columns reinforced with glass fiber–reinforced polymer (GFRP) and carbon fiber–reinforced polymer (CFRP) longitudinal bars and transverse reinforcement. The database analysis indicates that reducing spiral pitch from relatively wide spacing (100–120 mm) to dense configurations (35–40 mm) leads to a significant increase in normalized axial strength (approximately 50–100%) and enhances post-peak stability. Increasing concrete compressive strength from 30 to 50 MPa is associated with an increase in peak load of approximately 20–40%, accompanied by a reduction in ductility of about 25–35%. Columns reinforced with CFRP generally exhibit higher axial capacity than their GFRP counterparts, with observed strength gains in the range of 15% to 50%, primarily due to the higher stiffness and confinement efficiency of CFRP. Geometric effects are also pronounced. Circular columns tend to provide 10–25% higher normalized capacity compared to square sections. In addition, increasing column slenderness (higher L/D ratio) is associated with reductions in axial strength of approximately 20–30%, reflecting the influence of stability and second-order effects. A nonlinear finite element model was employed to support and extend the experimental trends observed in the database analysis. The numerical simulations captured consistent behavioral patterns, confirming the sensitivity of peak load and post-peak response to confinement intensity, concrete strength, FRP stiffness, and slenderness ratio. Comparisons with common design provisions indicate generally good agreement between predicted and experimental strengths, with experimental-to-predicted ratios typically ranging from 0.95 to 1.10, although both conservative and unconservative predictions are observed, particularly for lightly confined or slender columns. The combined experimental synthesis and numerical validation provide a unified understanding of the governing mechanisms controlling the axial behavior of FRP-RC columns and offer a strengthened basis for future refinement of design recommendations.