Browsing by Author "Fataar, Humaira"
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- ItemFatigue behaviour of steel fibre reinforced concrete(Stellenbosch : Stellenbosch University, 2022-04) Fataar, Humaira; Combrinck, Riaan; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Concrete is a heterogeneous material that is known to have a weak tensile capacity. The construction industry has successfully utilised steel reinforcement in concrete to overcome its brittle tensile behaviour, however, steel reinforcement is generally not sufficient to resist the formation and propagation of tensile cracks. As a result, discrete fibres are added to the concrete mixing stage to produce fibre reinforced concrete (FRC). The use of steel fibres has been known to improve the post-cracking behaviour of steel fibre reinforced concrete (SFRC), and is one of the most readily available fibres in industry. Due to concrete’s popularity as a construction material, many of its applications may experience flexural fatigue loading at some point during its lifespan. A significant amount of research has been conducted on the fatigue behaviour of plain concrete and FRC in the past century. However, the research focused primarily on the uncracked behaviour, with few researchers considering the cracked behaviour. In FRC, the fibres are activated only at crack initiation and therefore, this work aimed to investigate the fatigue life and failure mechanisms of pre-cracked SFRC subjected to fatigue loading. Experiments were conducted at a single fibre and macroscopic level, using hooked-end steel fibres. The pre-cracks ranged from 0.6 mm to 2.5 mm, at fatigue load levels of 50%, 70% and 85% of the maximum static load. Various methods were used to attempt to predict the fatigue life and failure mechanisms. A single fibre pull-out model was developed to categorise the various fibre pull-out phases and the level of deformation associated with each phase. When subjected to a static pre-slip of the fibre, followed by fatigue loading, the failure mechanisms were both fibre pull-out and fibre rupture. The fatigue capacity and failure mechanisms of the single fibre specimens vary depending on the combination of pre-slip and load level. The pull-out failures are generally unable to resist many load cycles due to a diminished fibre anchorage. The rupture failures tend to occur after a significant number of cycles have already passed, since the fibres rupture due to fatigue failure. The macroscopic behaviour subjected to fatigue loading shows fibre rupture to be the dominant failure mechanism, which differs from the static behaviour, where fibre pull-out occurs. The fatigue resistance decreases with an increase in pre-crack and load level. The single fibre pull-out model is used to classify the fibres into the different phases along the height of the crack for the various pre-cracks. A fatigue life prediction approach developed from the macroscopic fatigue results in the form of a modified S-N curve, was used to predict the fatigue behaviour. Experimental results from similar work performed was compared with the modified S-N curve and the results show that for deflection softening behaviour of SFRC, the model overestimates the fatigue capacity. Therefore, post-cracking behaviour influences the fatigue capacity of SFRC. The framework for an analytical model was developed to predict the fatigue failure mechanisms of pre-cracked SFRC. Fibre pull-out is likely to occur when large pre-cracks are present, whereas fibre rupture is more likely at low pre-cracks.