Experimental and theoretical behaviour of reinforced concrete beams containing hybrid fibres

The use of fibres of different sizes are needed to improve the control of multi-level cracking of reinforced concrete (RC). There are several studies of the use of hybrid fibres for this purpose, however, there is limited work on the finite element modelling (FEM) of fibres in crack arresting of RC beams. In this study, fifteen RC beams containing silica fume, polyvinyl alcohol (PVA), polypropylene (PP), or hybrid fibres were experimentally tested and then finite element analysis (FEA) was conducted using ATENA 3D. The fibres were used up to 2.5% in the beams which were reinforced with and without shear reinforcement. All the beams were tested under four point bending with span to depth (a/ d) ratio of 2.25. It was found that the PP, PVA fibres, and their hybrid in RC beams showed higher ductility in terms of multiple cracking before failure as compared with control beam without fibres. It was noticed also that PVA fibre showed a relatively greater flexural strength and recovery effect compared to PP fibre. Adding more than 1.5% PVA or hybrid fibres (1.5% PVA and 0.375% PP) without shear reinforcement contributed towards increasing shear capacity and ductility compared to the control beam containing shear reinforcement without fibres. A combination of small amount of hybrid fibres (0.75% PVA and 0.75% PP) and stirrups reinforcement resulted in a higher shear strength and higher ductility compared to other studied beams without shear reinforcement, which contain PVA, PP fibres up to 2.5% or hybrid fibres (1.5% PVA and 0.375% PP). A simple empirical equation based on the ACI-code 318-19 was used for predicting the shear behaviour of the studied beams taking in to consideration the effect of hybrid fibres for predicting the shear strength of the studied beams in a simple and accurate way. Based on the results of this investigation, it is recommended that a combination of hybrid fibres (0.75% PVA and 0.75% PP) and stirrups reinforcement (7.5 empty set 6 /m) should be used to achieve adequate shear behaviour of hybrid fibre reinforced concrete beams. The FEA results of all beams showed a good correlation with the experimental results in terms of the maximum load, load versus deflection and crack patterns.