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UBC Theses and Dissertations

Fibre reinforced concrete in shear and flexure Henley, Julien


An experimental investigation into the effect of steel fibres on the shear strength of concrete beams and slabs containing no transverse reinforcement is presented. Eight slab elements were tested in the UBC Element Tester and eight beams were tested under third point loading. A number of combinations of concrete strength and fibre volumes were considered in the experimental program. The concrete strength was varied from 25 MPa to 95 MPa while the fibre content ranged from 0% to 1.5% by volume. The beams showed an increase in shear strength of up to 80 % when 1.5 % by volume of steel fibres were added to the concrete. Apart from considering the ultimate shear strength of the slabs and beams, the effect of steel fibres on crack widths and modes of crack opening was also considered. A method is presented to include the effect of steel fibres in predicting the flexural strength of steel fibre reinforced concrete sections. Previous results on the pull-out strength of individual fibres were used to define the tensile response of fibre reinforced concrete at a crack. With this proposed stress-strain relationship it is possible to predict the flexural response using a traditional strain compatibility based procedure. A tensile stress block is also derived to simplify flexural predictions. These methods are then compared to experimental results and show favourable agreement. Some possible additions to the Modified Compression Field Theory (MCFT) are suggested to account for the increase in shear strength due to steel fibres. To include the effect of steel fibres in a rationally based method for the shear strength of members containing no transverse reinforcement, the following areas are considered: the average post-cracking tensile response of concrete, the ability of a crack to transmit shear force by aggregate interlock and the crack spacing. The theoretical predictions are compared to the experimental results and some additional experimental work and show promise.

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