Are steel fibres able to mitigate or eliminate size effect in shear?

Abstract

This paper reports some recent results of an experimental campaign on fibre reinforced concrete (FRC) beams under shear loading tested at the University of Brescia: nine full scale beams, having a height varying from 500 to 1,500 mm, were tested for investigating the effect of steel fibres on key-parameters influencing the shear response of concrete members, with special emphasis on size effect. All tested members contained no conventional shear reinforcement and different amounts of steel fibres: 0, 0.64 or 1 % by volume. Results show that a relatively low volume fraction of fibres can significantly increase bearing capacity and ductility. The latter determines visible deflection and prior warning of impending collapse, which is not possible in plain concrete beams (without transverse reinforcement). The size effect issue is substantially limited. Results were compared against the shear formulation incorporated in the final draft of fib Model Code, which can be considered a valuable analytical model for FRC beams under shear loading, even in the case of the three deepest elements herein tested

Experimental analysis of the efficiency of steel fibers on shear strength of beams

“…In fact, δu,SFRC/δu,SC increased when fibers were added to the concrete. Fiber capacity, when dosed adequately, modified the failure mode from shear to flexure, corroborating conclusions by You et al (2010), Minelli et al (2014) and Tahenni et al (2016). Therefore, V-δ showed that SFRC beams (V0.5, V0.8 and V1.0) had a predominantly ductile behavior, where the control beam, V0, revealed a fragile behavior.…”

Influence of concrete matrix and type of fiber on the shear behavior of self-compacting fiber reinforced concrete beams

“…Therefore, a degree of crack redistribution may be established by allowing a progressive shear crack growth up to failure, with an increase in bearing capacity and ductility. For the same load level, FRC elements show a more distributed crack pattern with more closely spaced and smaller cracks [7]. On the other hand, shear crack width evolution was analyzed during the test (Fig.…”

“…SFRC makes it possible to obtain a more widely distributed cracking pattern, with smaller crack widths and less separation between cracks [4,6]. Fibers could even avoid the formation of a single critical shear crack and delay the occurrence of the shear failure mechanism [7], enhancing bearing capacity, mitigating the size effect in shear or guaranteeing the minimum shear reinforcement required by the current Codes [6]. The ability of SFRC to convert brittle concrete behavior to ductile has been extensively studied [2,5,6,8,9].…”

High performance fiber reinforced concrete for the shear reinforcement: Experimental and numerical research

“…Concrete shear behavior is reported as one of the most significant enhancements achieved by adding fibers to the concrete matrix [8,9]. The experimental evidences confirmed the efficiency of fibers as shear reinforcement to enhance the ultimate shear capacity and ductility of the structural elements [10,11]. The steel fibers increase the bearing capacity of the concrete elements and, therefore, bring the member up to yielding of rebars [12].…”