Flexural behavior of rectangular FRP-tubes filled with reinforced concrete: Experimental and theoretical studies

This paper presents experimental and theoretical investigations on the flexural behavior of rectangular concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) beams with steel rebar. Seven full-scale CFFT beams, 3200 mm long and 305 × 406 mm2 cross section, were tested under a four-point bending load and were compared to two control steel-reinforced concrete (RC) beams. The CFFT beams had the same flexural steel reinforcement, but they had different wall thicknesses of filament-wound FRP tubes. The experimental results indicate an outstanding performance of the CFFT beams in terms of strength and energy absorption compared to the RC beams since their flexural strength and energy attained values 344% and 1052% higher than that of the RC beams, respectively. A strain compatibility/equilibrium model was developed to predict the moment-curvature response of the CFFT section addressing the issue of confinement and tension stiffening of concrete. The analytical results match well the experimental results in terms of moments, curvature, strains, and neutral axis location. Based on the model, the deflection can be predicted by integrating the curvatures along the span of the flexural member.