Incorporation of micro-cracking and fibre bridging mechanisms in constitutive modelling of fibre reinforced concrete

The formation and propagation of cracks under progressive loading in fibre reinforce concrete (FRC) are significantly influenced by fibre bridging mechanisms. Cracking and fibre bridging, governed by the FRC constituents and their properties, are two coupled and interacting phenomena that significantly affect the ductility and transition from diffuse to localised deformation. Constitutive modelling of FRC is challenging due to the high inhomogeneity and complex transition of deformations stages rooted from the difference in responses of cracked and intact material volumes coupled with cohesive resistance and fibre bridging of a crack. In this paper, a new approach to constitutive modelling of FRC is developed by enriching the constitutive structure to accommodate different responses of the crack, intact material and fibres. The strain discontinuity caused by cracks is accounted for via an enriched strain field which facilitates the introduction of the two interacting mechanisms, cohesive cracking and fibre bridging, in the constitutive model. The transition from diffuse to localised deformation is controlled by the fibre volume content and local deformation, via the density of active cracks. It is demonstrated that the proposed constitutive model is capable of describing the transition from diffuse to localised deformation associated with different macro responses under different loading conditions.