Flexural strength and behavior of steel and FRP-reinforced concrete-filled FRP tube beams

The flexural strength and behavior of reinforced concrete-filled fiber-reinforced polymer (FRP) tube (RCFFT) beams were investigated experimentally and theoretically. A total of ten beams were tested under four-point bending load. Six beams were reinforced with glass FRP bars while the rest were reinforced with conventional steel bars. Filament winded glass FRP tubes were used to act as stay-in-place formwork for the beam specimens. The test variables were the FRP tube thickness, concrete compressive strength, type of internal reinforcement (steel or FRP bars), and type of transverse reinforcement (spiral steel or FRP tube). Yield and ultimate strengths, failure modes, and ductility are discussed based on measured load, deflection and strain data. The test results indicated that the confinement using FRP tubes provided a potential enhancement in the ductility and strength of tested beams. A simplified analytical method was developed to predict the yield and resisting moments corresponding to the failure modes of the tested RCFFT beams. The analysis was conducted according to the equations derived from linear elastic analysis. This analysis was found to be acceptable for predicting the ultimate and yield moment capacities of the beams. In addition, improvement to the crack moment equation was suggested to account for the effect of confinement using FRP tubes.