Replacement of stirrups by steel fibers in shear dominant UHPFRC beams

Abstract

In the present study, the impacts of variety of fiber types and amounts on shear dominant Ultra High Performance Fiber Reinforced Concrete (UHPFRC) beams and the feasibility of fully replacement of stirrups by the steel fibers were investigated. Fifteen UHPFRC beams containing five different fiber types and three volume fractions were prepared without stirrup and were loaded under four-point loading. The influences of steel fiber were discussed in terms of the load-deflection behavior, cracking behavior, collapse modes, ultimate shear strength, nominal moment capacity and deflection ductility. The steel fiber use prominently increased the post-cracking stiffness and load capacity of the UHPFRC beams with the help of the fibers' crack-bridging ability. Conversely, the steel fibers in different types didn't have an importance on the collapse mode of the shear dominant UHPFRC beams. The use of straight steel fibers in the UHPFRC beams, even at very low volume fractions of 0.5 percent, changed the collapse condition from shear to flexure resulting in a ductile behavior. But the hooked fiber inclusion by 1.5 vol percent percent at least is needed to guarantee the flexural behavior regardless of hooked or multi hooked-end form.