Shear behavior of SFRC beams reinforced with FRP stirrups: Experimental and analytical investigations

The shear properties of eight steel fiber reinforced concrete (SFRC) beams reinforced with glass fiber reinforced polymer (GFRP) stirrups, referred to as GFRP-R-SFRC beams, are reported under four-point loading. Two parameters of the volume fraction of steel fibers (V_f) and the shear span ratio (λ) are considered, and their effects on the failure mode, mid-span deflection, crack width, strains of SFRC and longitudinal rebars, and shear capacity of GFRP-R-SFRC beams are then investigated. As the λ increases from 1.5 to 3.0, the GFRP-R-SFRC beams sequentially experience three failure modes: diagonal compression failure, shear compression failure, and diagonal tension failure. The incorporation of 1.5% steel fibers results in a reduction of the maximum deflection, maximum crack width, rebar strain and concrete strain by 2.3%, 16.8%, 15.7%, and 5.1%, respectively, indicating an enhancement in the post-cracking stiffness of GFRP-R-SFRC beams. Due to the crack-bridging effect of steel fibers, the average strain, maximum strain, and utilization ratio of GFRP stirrups increase with the increase of V_f. The shear capacity of GFRP-R-SFRC beams increases by 25.6% as the V_f increases from 0% to 1.5%, and the enhancement in shear capacity (25.6%) due to the addition of steel fibers shows a similar effect to that observed in conventional SFRC beams (12.7%). However, an increase in λ leads to a decrease in shear capacity, as the failure mode of the beam shifts from a shear-dominated pattern to a flexure-dominated pattern, which is similar with conventional SFRC beams. Considering the positive contribution of steel fibers, a modified computational model is proposed for evaluating the shear capacity of FRP-R-SFRC beams. A good agreement between the predicted and experimental results is shown.