Shear resistance of reinforced concrete beams with and without steel fibres
The fabrication and placement of conventional shear rein- forcement are time consuming and costly and its use in thin structural concrete members is often impractical. Fibre reinforcement is known to control flexural and shear cracking and can therefore be used to replace conventional shear reinforcement. This investigation consists of experimental and theoretical studies into the use of crimped steel fibres as shear reinforcement in reinforced concrete beams. Eighteen reinforced lightweight concrete beams with thin web were fabricated and tested under four point loading. The para- meters studied were the fibre content, the shear span/effective depth ratio and the amount of main steel. Subsidiary tests on concentric pull-out specimens and shear transfer specimens were carried out to study- the influence of steel fibres on the bond stress slip characteristics of a deformed bar (Tor Bar) and the stiffness and ultimate strength of the shear-transfer mechanism across a definite plane respectively. The inclusion of fibres increased the ultimate strength of the beams by 63 to 211.5%. Fibre concrete beams had more flexural and shear cracks and showed substantially greater ductility at failure than their plain concrete counterparts. The fibres in the pull-out specimens were effective in controlling the splitting cracks and transforming a sudden bond failure into a gradual one. The fibres increased the ultimate shear strength of the shear transfer specimens by 9.9 to 101.8%. The stiffness of the shear transfer mechanism was not, however, significantly affected. A simple approach based on the Standard Method of the CEB-FIP Model Code is proposed to determine the ultimate shear resistance of fibre reinforced concrete beams. It predicts adequately the ultimate shear strength of steel fibre reinforced concrete beams. A nonlinear 3-dimensional finite element model was developed to predict the entire structural response up to failure of both plain and fibre reinforced concrete beams subjected to short_. term monotonically increasing loading. The concrete is represented by 8-nodeisoparametric hexahedra and the tension steel by bar elements. The finite element model predicts satisfactorily the structural behaviour of both plain and fibre reinforced concrete beams.