Evaluation of the experimental curvature ductility of RC beams externally strengthened with CFRP bands

Abstract

This paper presents an experimental research about bending response of a set of reinforced concrete beams strengthened with external CFRP (RCB-SCFRPs). The aim of the research was to make an evaluation of curvature ductility using experimental data and to generate simplified expressions to estimate the ductility of RCB-SCFRP. In addition, the experimental behavior and the resulting failure modes on bending are also studied by experimental tests. Seventeen natural-scale RCB-SCFRPs with different configurations of reinforced steel bars and FRP (Fiber-reinforced polymer) bands from three manufacturers are designed and loaded under monotonic four points bending tests. In fact, three groups of RCB-SCFRPs were designed in order to evaluate the effect of FRP longitudinal ratio and the external transverse FRP reinforcement (Groups I and II) and to obtain the failure bending modes described in ACI 440.2R [1] (Group III).Flexural capacity and curvature ductility are some of the most important and well-known parameters for analysis and design of traditional RC beams. The calculation of these same parameters in the application of RCB-SCCFRP is not straightforward to compute. Because of this difficulty, the present research focuses on the study of bending behavior and evaluating ductility in terms of FRP axial rigidity, and the steel and CFRP reinforcement ratio.For this purpose, the experimental bending moment-curvature (M-Ф) diagrams were constructed using a proposed approach based on geometric compatibility. The effect of the transverse FRP reinforcement such as U-clamps is not completely clear, but in most cases, the RCB-SCFRPs with transverse reinforcement showed the best performance in final curvature and a greater ductility. Test results indicate that the RCB-SCFRP bending behavior was critically influenced by the FRP properties. Additionally, the FRP axial rigidity had a critically adverse effect on the curvature ductility of the RCB-SCFRPs tested.Furthermore, several expressions based on internal forces equilibrium for predicting the failure bending mode and curvature ductility of RCB-SCFRPs are proposed, which are consistent with experimental data.Finally, a simplified method is proposed to obtain a well-estimated value of curvature ductility considering FRP axial rigidity and steel reinforcement ratio, which could be very helpful to the researcher and designer engineer.