Ductile‐to‐brittle transition in fibre‐reinforced concrete beams: Scale and fibre volume fraction effects

Abstract

The mechanical response of fibre-reinforced brittle-matrix structural elements subjected to bending is discussed in the framework of fracture mechanics. By means of numerical simulations based on the bridged crack model, the flexural behaviour of steel fibre-reinforced concrete (FRC) beams has been investigated, taking into account pull-out or yielding bridging mechanism of the secondary phase. In both cases, the numerical results predict a transition of the global structural behaviour, which can range from ductile to catastrophic. This behaviour is governed by a dimensionless parameter, the brittleness number, N P , in which the effects of the structural size and the fibre volume fraction are included. An experimental campaign is carried out on FRC beams subjected to three-point bending tests, considering three different beam sizes and four different fibre contents. A comparison between experimental tests and numerical simulations shows that the bridging mechanism is due to the fibre slippage into the matrix, rather than the fibre plastic flow. The expected ductileto-brittle transition is found for each beam scale, as predicted by N P. As a consequence, the minimum fibre volume fraction can be defined according to this model, providing an effective structural bearing capacity of FRC structural members.

Tensile behaviour identification in Ultra-High Performance Fibre Reinforced Cementitious Composites: indirect tension tests and back analysis of flexural test results

“…This evidence can be ascribed to two main reasons: (1) the well-known scale-effect (even significantly affecting concrete response depending on specimen geometry for both notched and un-notched samples [27][28][29][30]) and (2) the influence played by beam production on fibre alignment (as discussed in Sect. 2.2).…”

Effect of reinforcement on the crack resistance of concrete slabs

“…In [11] the effect on the crack resistance of a concrete sample of a system of steel reinforcing bars located in it in a plane perpendicular to the external bending moment as a vector was investigated. In this case, some of these rods passed through the faces of a flat edge crack, which was postulated in the cross-section of the sample.…”

The Threshold for Under-Reinforced Concrete Sections Proposed by ACI 318, EC 2 and BS 8110

“…The ductile behavior of reinforced concrete (RC) cross-sections has always been desirable for building codes and standards. However, the threshold to distinguish ductile and brittle behavior of RC cross-sections proposed by building codes has yet to be evaluated [1][2][3][4]. This behavior mainly depends on the type of RC cross-section whether it is under-or over-reinforced.…”