A novel approach to characterize the direct shear pullout behavior of single hooked steel fibers

Fibers crossing sliding crack planes have a positive influence on capacity because they can transfer shear load as dowels. Such behavior was evidenced by several researches that investigated the direct shear performance of Fiber-Reinforced Concrete. However, there is limited literature on the direct shear pullout behavior of single fibers, which certainly provides a deeper understanding of the mechanisms involved in direct shear. Therefore, this paper presents a new approach to perform direct shear pullout (or dowel pullout) of single fibers with a developed portable test apparatus, which enables performing the typical pullout with aligned fiber and load as well. From the comparison between the dowel and aligned pullouts, the energy dissipation capacity and the bond strength of the samples tested under direct shear were found 3.13 and 1.77 times greater than the aligned ones, respectively. The remarkable differences are attributed to the increase in fiber/matrix friction due to the shear load and the continuous occurrence of plastic strains, evidenced by the fiber shape at the end of the dowel pullout. Both mechanisms can be associated with the snubbing effect. Furthermore, the test methodology presented small coefficients of variation (CV) for pullout work and bond strength. For the direct shear pullout, the CVs were 9.57% and 10.42%, respectively, and for the aligned pullout were 16.73% and 18.95%, respectively113CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES427720/2018–4180475