Yield-line-based design of fibre-reinforced concrete: assessment of suitability of material models

The aim of this research was to assess the adequacy of material models based on flexural toughness (such as equivalent and residual flexural strength) and the deflection limits at which these parameters are estimated for the design of fibre-reinforced concrete (FRC) for various applications such as slabs-on-grade and pavements. The experimental work was conducted using FRC mixes with hooked-end steel fibres (SF) or macro polypropylene fibres (PF) and hybrid combinations of SF and PF. Toughness testing was carried out on unnotched and notched prisms and square slabs, prepared with a typical grade of concrete used for FRC pavement applications. To validate the material models, comparisons were made between the theoretical moment/load calculated based on material flexural toughness parameters and the actual moment obtained from slabs using the yield line formed during testing. It was found that, overall, both equivalent flexural strength (from unnotched prism tests) and residual flexural strength (from notched prism tests) are suitable for designing FRC slabs. However, the equivalent strength showed better correlation to the slab response. Hybrid PF–SF mixes with a higher volume fraction of 0.6% showed a marginal increase in flexural performance compared with mixes with a lower volume fraction but no or minimal synergy due to hybridisation.