Shear Strength Model for Steel Fiber Reinforced Concrete Beams without Stirrup Reinforcement

Abstract

A simple model is presented to estimate the shear strength of steel fiber reinforced concrete (FRC) beams without stirrup reinforcement. The model was developed on the basis of observations from tests of 27 large-scale beams under monotonically increased concentrated loading. Three types of hooked steel fibers were evaluated in volume fractions ranging between 0.75% ($59\mathrm{kg}/{\mathrm{m}}^3$ or $100\mathrm{lb}/{\mathrm{yd}}^3$) and 1.5% ($118\mathrm{kg}/{\mathrm{m}}^3$ or $200\mathrm{lb}/{\mathrm{yd}}^3$). All but one beam failed in shear either prior to or after flexural yielding. In the proposed model, shear in steel FRC beams is assumed to be resisted by shear stress carried in the compression zone and tension transferred across diagonal cracks by steel fibers. Shear carried in the compression zone is estimated by using the failure criterion for concrete subjected to combined compression and shear proposed by Bresler and Pister. The contribution from fiber reinforcement to shear strength, on the other hand, is tied to material performance obtained through standard ASTM 1609 four-point bending tests. Comparison of predicted versus experimental shear strengths for a large number of FRC beams tested in this and other investigations indicates that the proposed model is capable of predicting the shear strength of steel FRC beams with reasonable accuracy; mean and standard deviation values are 0.79 and 0.12, respectively.