Structural behavior of GFRP-concrete composite columns under axial load

Glass Fiber Reinforced Polymer (GFRP) is a promising alternative to steel due to its high strength, lightweight properties, corrosion resistance, and low maintenance requirements. This study examines the effect of internal GFRP I-sections on the axial load capacity and fire resistance of reinforced concrete (RC) columns. The experimental program consisted of two groups: the first group, conventional RC columns, with one exposed to 500°C for 90 minutes and the other unheated, and the second group, GFRP I-section reinforced columns, similarly tested under fire and control conditions. Results show that GFRP-reinforced columns exhibited a 17% higher axial capacity than conventional RC columns. However, fire exposure reduced the axial strength of GFRP-reinforced columns by 39% compared to unheated specimens and by 14% compared to conventional RC columns. Theoretical axial load capacities were calculated using design codes, and finite element analysis (FEA) validated the experimental results. Additional parameters, including concrete strength, steel yield strength, reinforcement ratio, and GFRP section properties, were analyzed. The strong correlation between experimental, theoretical, and numerical results provides a foundation for developing practical design guidelines for GFRP-reinforced composite columns.