Circular Concrete Columns and Beams Reinforced with GFRP Bars and Spirals under Axial, Eccentric, and Flexural Loading

Abstract

Glass fiber-reinforced polymer (GFRP) reinforcement has been considered as a replacement for the traditional steel reinforcement, mainly due to its corrosion resistance. In this paper, a total of 13 concrete columns and beams (length/diameter = 5.3) fully reinforced with GFRP longitudinal bars and spirals were experimentally studied. An additional two reference columns were also constructed with steel rebars and GFRP spirals to quantify the effect of the long bars. Factors such as the number of longitudinal bars, the pitch of the spirals, and load eccentricities were examined. It was found that the load capacities of the specimens with GFRP reinforcement were up to 12.3% lower than those with steel reinforcement; however, with sufficient transverse reinforcement, the GFRP-reinforced specimens were up to 15% more ductile. Reducing the pitch of the GFRP spirals and increasing the number of longitudinal reinforcing bars both resulted in an increase in the ductility and load capacity, demonstrating the contribution of transverse and longitudinal reinforcement. Strains well beyond the ultimate strain capacity of the concrete were measured in the longitudinal GFRP bars, illustrating the significant confinement provided by the spirals. The experimental results were favorably underpredicted by the recommended simplified method derived in this paper. In order to simplify the design process of circular members, a factor βc was introduced to the current design rules in the international design standards and validated by the experimental results.