Compressive Response of Concrete Confined with Steel Spirals and FRP Composites

This article presents the results of an experimental and analytical study on the behavior of concrete cylinders externally wrapped with fiber-reinforced polymer (FRP) composites and internally reinforced with steel spirals. The experimental work was carried out by testing twenty-four 150 × 300 mm ² concrete cylinders subjected to pure compression with various confinement ratios and types of confining material. The test results show that the compressive response of concrete confined with both FRP and steel spirals cannot be predicted by summing the individual confinement effects obtained from FRP and steel spirals. This is largely attributable to differences in the inherent material properties of FRP and steel. A new empirical model to predict the axial stress-strain behavior of concrete confined with FRP and steel spirals is proposed. Comparisons between experimental results and theoretic predictions show agreement.