Experimental and analytical investigation on structural behavior of two-layer fiber-reinforced concrete beams reinforced with steel and GFRP rebars

Abstract

The combination of plain concrete and fiber-reinforced concrete in beams in the form of two-layer composite members can be an efficient solution to improve the flexural behavior, reach the optimum distribution of steel fibers, and reduce the cost of these structural elements. On the other hand, the glass fiber reinforced polymer (GFRP) rebar can serve as a proper alternative for the steel rebar in reinforced concrete beams considering its superior strength to weight ratio compared with the steel rebar. The objective of this research was to evaluate the structural performance of two-layer fiber-reinforced concrete beams with glass fiber-reinforced polymer (GFRP) and steel rebars under quasi-static loads. For this purpose, three groups of concrete beams reinforced with GFRP rebars and four groups of concrete beams reinforced with steel rebars were fabricated with one- and two-layer sections containing different volume fractions of steel fibers (Vf = 0, 0.75, and 1.5%), without using shear reinforcement. The longitudinal reinforcement ratios were 0.37 and 0.73% for GFRP and 1.05 and 2.1% for steel rebars, and the concrete compressive strengths were 33 and 64 MPa. The fabricated beams were then tested under three-point bending. The results of the layered concrete beams showed that adding fibers to the compression zone of the section led to a higher ductility in both GFRP rebar- and steel rebar-reinforced beams, while adding fibers to the tensile zone led to a higher ultimate flexural strength. Furthermore, an increase in the ratio of GFRP and steel reinforcement together with a greater concrete compressive strength in the layered beams enhanced their flexural performance in terms of load-carrying capacity, flexural stiffness, and ductility; however, replacing steel rebars with GFRP ones led to a decrease in these parameters. Finally, the flexural response of the layered concrete beams reinforced with GFRP and steel rebars was predicted via sectional analysis and using empirical equations developed for the mechanical properties of the constituent materials. The analytical results indicated a good agreement between the proposed model and the experimental results, to the extent that the model was able to properly predict the flexural behavior of the layered concrete beams in terms of the ultimate load-carrying capacity and mid-span deflection.