Experimental and numerical investigation of the effect of steel fibres on the deflection behaviour of reinforced concrete beams without stirrups

This paper presents an experimental and numerical study of the effect of steel fibres on the deflection behaviour and the contribution to the stiffness of tensioned concrete made by steel fibres reinforced concrete (SFRC) beams without stirrups, tested under four-point bending. The main testing parameters were the compressive strength of the concrete, the volume fraction of the fibres and their aspect ratio. The experimental deflections measured at mid-span of the beams were compared with the theoretical values predicted by three major design codes for reinforced concrete (RC) structures: the American ACI 318, the European Eurocode 2, the New Zealand NZS 3101, and also that predicted by Alsayed's model. In the present study, a new model is proposed, taking account of the volume fraction, the aspect ratio and the orientation of the steel fibres. The instantaneous deflections predicted by the proposed model were compared with test results for SFRC beams extracted from the literature. The experimental results show that the deflection behaviour and the stiffness contribution of tensioned concrete increase with the addition of steel fibres. The proposed model yields reliable results and is found to be satisfactory in predicting the deflection of SFRC beams. In addition, the numerical ultimate load and corresponding mid-span deflection of beams predicted by non-linear finite element analysis using ANSYS (c) mechanical APDL software and considering four values of the fibre orientation factor (0, 0.45, 0.637 and 1), were compared with the experimental values. The predicted finite element results for the orientation factor of 0.45 are in close agreement with the experimental values. The numerical results show that the fibre orientation has a significant effect on the flexural behaviour of the SFRC beams.