Steel fibre reinforced concrete for elements failing in bending and in shear

Abstract

Discrete steel fibres can increase significantly the bending and the shear resistance of concrete structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a cross-section layered model and the material constitutive laws, the deformational behaviour of structural elements failing in bending was predicted from the moment-curvature relationship of the representative cross sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three point bending tests with shallow beams were performed. The applicability of the formulation proposed by RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the response of the SFRC beams failing in shear was predicted.

Modelling the flexural behaviour of fibre reinforced concrete beams with FEM

“…As it was stated by numerous researchers [3,5,[13][14][15][16][17][18][19][20][21][22], the stress-strain relation for the case of compression foresees an initial elastic behaviour followed by a peak plateau that eventually ends when the concrete crashes. For the case of the material behaviour in tension, the elastic region is significantly smaller given that the micro-cracks develop faster when the material is under tension and given the low ultimate tensile strength of concrete, the fibre reinforced material starts to deteriorate faster.…”

“…5, was formulated accordingly so as to numerically describe all main mechanical phases of the FRC material behaviour when under tension thus avoid over-simplifications (i.e. see [3,5]). …”

“…The first experimental setup that was modelled was the UHPFRCC beams that had no conventional steel reinforcement bars and were loaded under a three-point bending configuration, while a similar in geometry beam that was found in [3] was also analysed and is presented in Section 7.2. The second group of specimens that were modelled, was the four-point bending experiment also found in [3] presented by Barros et al, where a set of FRC beams with conventional steel rebars were experimentally and numerically studied under shear failure. Finally, in Section 7.4 a three-point test of a FRC beam with conventional rebars [19] was modelled and the numerical findings related to the prediction of its flexural behaviour are discussed.…”

“…[3]. In this research work [3] the proposed material model is integrated within a finite element beam which uses the layer approach so as to discretise the beam's section.…”

“…[3]. In this research work [3] the proposed material model is integrated within a finite element beam which uses the layer approach so as to discretise the beam's section. As it was mentioned in their work, each section of the beam finite element was discretized with three layers and the conventional steel reinforcement was also converted into layers so as to be included within the modelling framework.…”