Effect of test parameters on flexural strength of circular fiber-reinforced polymer-confined concrete beams

This paper presents experimental results of a study conducted to investigate the use of filament-wound fiber-reinforced polymer tubes as a stay-in-place structural formwork for concrete beams. The experimental study was carried out on a total of seven concrete-filled fiber-reinforced polymer tube beams of 213 mm diameter and 2000 mm long. Five concrete-filled fiber-reinforced polymer tube beams and two control specimens without tube were tested under four-point bending. One control specimen was reinforced with spiral steel while the other had no transverse reinforcement. The test parameters used in this investigation include the type of internal reinforcement (steel or glass fiber-reinforced polymer bars), the type of transverse reinforcement (spiral-steel or fiber-reinforced polymer tube), fiber-reinforced polymer tube thickness and the concrete compressive strength. The fiber orientations of the tubes were mainly in the hoop direction. The test result indicated that the two control specimens failed in shear; however, using glass fiber-reinforced polymer tubes instead of transverse spiral-steel changed the mode of failure of the five concrete-filled fiber-reinforced polymer tube beams to flexural failure. The experimental cracking moments of the steel and fiber-reinforced polymer-concrete-filled fiber-reinforced polymer tube beams were compared to theoretical predictions provided by North American codes, design guidelines and the available equations in the literature. The test results indicate that the fiber-reinforced polymer tube enhances the crack and ultimate moment capacities of the test specimens, whereas it provides a longitudinal reinforcement in the tension side. In addition, improvement to the crack moment equation is suggested to account for the effect of confinement.