Effect of steel fiber on flexural performance of bilayer concrete beams with steel and GFRP rebars: Experiments and predictions

Replacing steel rebars with glass fiber reinforced polymer (GFRP) rebars in concrete beams can lead to the production of lightweight and durable structural members. Meanwhile, layering concrete beams and using different volume fractions of steel fibers in the layers can be a proper method for improving structural performance and reducing construction costs of fiber reinforced-concrete beams. Therefore, this research aims to evaluate how bilayer steel fibrous concrete beam specimens with GFRP rebars behave under flexure. For this, 14 beam specimens reinforced with GFRP and steel fibers were manufactured in seven experimental groups without using any shear reinforcement. The effect of key variables such as reinforcement ratio, the volumetric content of steel fiber, and compressive strength of concrete on the performance of bilayer beams was examined. The main experiment of the current study involved three-point flexural tests, which were conducted on flexural specimens. The effective parameters on flexural behavior of beams such as flexural resistance, flexural stiffness, toughness, fracture energy, and load-displacement curve were extracted from the results. The results showed that the flexural properties of concrete beams increased by adding 0.75% steel fibers. Nevertheless, per the same fiber ratio, bilayer fibrous beam specimens had weaker flexural performance relative to one-layer fibrous concrete beam specimens. Additionally, when the GFRP bar was replaced with steel bar in the bilayer concrete flexural specimen, flexural resistance, toughness, fracture energy, and stiffness decreased while deflection in peak load increased significantly. Moreover, using high-strength concrete (HSC) in comparison to normal strength concrete (NSC) in bilayer GFRP reinforced beams improved flexural properties by almost 28%. After comparing the formulation to capture the flexural capacity of beam specimens in different specifications with results observed in this research, it is concluded that ACI 440.1R-06 and CAN/CSA S806-12 predict the deformation in service mode to great accuracy for beams reinforced with FRP as well as ACI 318, CAN/CSA A23.3, and ACI 440.1R-15 for steel-reinforced beams.