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Ultra-high-performance concrete (UHPC) is recognized for its exceptional strength, durability, and versatility in engineering applications, making it a reliable composite in the construction industry. The incorporation of fibres into UHPC enhances its mechanical properties. Non-metallic fibres offer a promising alternative to steel fibres due to their resistance to corrosion. While much research has focused on the shear behaviour of UHPC reinforced with steel fibres, there is a notable gap in understanding the impact of non-metallic fibres. This study aims to address this gap by comparing the influence of synthetic fibres to steel fibres on the shear behaviour of UHPC through numerical modelling. Finite element analysis (FEA) was conducted to simulate the shear behaviour of UHPC deep beams, incorporating 5D steel fibre, hooked-end steel fibres and Forta-Ferro (FF) synthetic fibres. The analysis was performed using the concrete damage plasticity (CDP) model within the ABAQUS software. To validate the finite element model (FEM), three deep beam specimens with varying dimensions, previously tested, were selected for comparison with experimental data. Key parameters investigated included fibre type and geometric dimensions, with an analysis of load-deflection curves, crack patterns, shear span-to-depth ratios ( λ ), length-to-depth ratios ( l / d ), and width-to-depth ratios ( b / d ) on shear capacity and mid-span deflection. Research findings indicate that, from a design perspective, the safe zone for maximizing the shear capacity of UHPC deep beams is defined by b / d and l / d ratios ranging from 0.19 to 0.25 and 2–3, respectively. Conversely, the risky zone, where shear capacity is minimized, corresponds to b / d and l / d ratios between 0.3 and 0.375 and 2.25 and 2.75, respectively. Since the ACI 318–19 standard does not specifically address the effects of the b / d and l / d ratios on UHPC deep beam shear behaviour, the results of this research offer valuable insights for improving current standards. Finally, UHPC deep beams reinforced with 0.11 % FF synthetic fibres achieve, on average, 85.97 % of the shear capacity of those reinforced with 0.76 % 5D steel fibres, suggesting that FF synthetic fibres can be a reliable alternative to 5D steel fibres due to their corrosion resistance and lower cost.
Mirzaaghabeik et al. (Mon,) studied this question.