Abstract
Through proper arranging of a hybrid combination of longitudinal fiber reinforced polymer (FRP) bars and steel bars in the tensile region of the beam, the advantages of both FRP and steel materials can be sufficiently exploited to enhance the flexural capacity and ductility of a concrete beam. In this paper, a methodology for the flexural strength design of hybrid FRP-steel reinforced concrete (RC) beams is proposed. Firstly, based on the mechanical features of reinforcement and concrete and according to the latest codified provisions of longitudinal reinforcement conditions to ensure ductility level, the design-oriented allowable ranges of reinforcement ratio corresponding to three common flexural failure modes are specified. Subsequently, the calculation approach of nominal flexural strength of hybrid FRP-steel RC beams is established following the fundamental principles of equilibrium and compatibility. In addition to the common moderately-reinforced beams, the proposed general calculation approach is also applicable to lightly-reinforced beams and heavily-reinforced beams, which are widely used but rarely studied. Furthermore, the calculation process is properly simplified and the calculation accuracy is validated by the experimental results of hybrid FRP-steel RC beams in the literature. Finally, with the ductility analysis, a novel strength reduction factor represented by net tensile steel strain and reinforcement ratio is proposed for hybrid FRP-steel RC beams.
Highlights
The use of fiber reinforced polymer (FRP) as longitudinal reinforcement of concrete members has gained popularity due to its advantages, such as high strength, light weight, and non-corrosive properties
A novel strength reduction factor represented by net tensile steel strain and reinforcement ratio is proposed for hybrid FRP-steel reinforced concrete (RC) beams with the common flexural failure modes through ductility analysis
Corresponding to the aforementioned three types of flexural failure modes, the features of strain distribution on a cross-section of hybrid RC beam at the ultimate state could be schematically illustrated by Figure 1, where the letters FM and BFS stand for failure mode and balanced failure state, respectively, and the number next to the letters represents the specific category of failure mode and state defined in this study, respectively
Summary
The use of fiber reinforced polymer (FRP) as longitudinal reinforcement of concrete members has gained popularity due to its advantages, such as high strength, light weight, and non-corrosive properties. The load-carrying capacity, deflection, crack widths, and deformability of hybrid-reinforced concrete beams were predicted by the presented models. Based on the conventional sectional analysis, Kara et al [11] proposed the advanced moment-curvature relationship considering tension stiffening effect and numerically predicted the flexural capacity and the ultimate displacement of hybrid FRP-steel RC beams characterized by the possible flexural failure modes. Pang et al [17] analytically derived the proper reinforcement ratio limits to ensure the ductile failure of hybrid GFRP-steel RC beams and predicted the flexural strength. Experimentally studied the flexural behavior of hybrid GFRP-steel RC beams including response stages, failure modes, crack patterns, stiffness, toughness and ductility. A novel strength reduction factor represented by net tensile steel strain and reinforcement ratio is proposed for hybrid FRP-steel RC beams with the common flexural failure modes through ductility analysis
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