Behaviour of High-Strength Concrete Circular Columns Reinforced with GFRP Bars and Spirals Under Simulated Seismic Loading

Circular reinforced concrete (RC) columns have many advantages compared to rectangular or square ones such as higher confinement efficiency and more appealing aesthetic appearance. The differences between the mechanical properties and behavior of FRP reinforcement with respect to steel include, but not limited to, the linear elastic behavior of FRP without yielding, lower strain capacity and different compressive and shear strengths. These properties significantly affect the response of FRP-RC columns as they directly affect confinement behavior. In addition, the seismic response and energy dissipation are greatly affected when FRP reinforcement is used. Therefore, developing independent code provisions for FRP-RC members is necessary. The experimental data available for FRP-RC circular columns under seismic loading, especially columns constructed with high-strength concrete (HSC), is very limited. Hence, the current provisions of the Canadian code for FRP-RC columns are very conservative, particularly for HSC, compared to those for steel-RC counterparts. In this study, two full-scale GFRP-RC circular columns were constructed and tested under a simultaneous seismic and axial loading. One specimen was constructed using HSC with 85 MPa concrete compressive strength, while normal-strength concrete (NSC) with 35 MPa was used for the other specimen as reference. Both test specimens had 350-mm diameter, 1,750-mm shear span, 1.2% longitudinal reinforcement ratio, with 85 mm spiral pitch. The results showed that the confinement requirements of the Canadian code for circular columns could be too conservative for NSC columns, while this is not the case for HSC ones, which need much more confinement reinforcement.