Dual cohesive elements for 3D modelling of synthetic fibre-reinforced concrete

In this paper, we introduce a novel computational approach that describes dual scale discontinuities where the fibres and fractures interfere and influence the overall behaviour of a structure. A mathematical formulation is proposed in alignment with the finite element method to take into account the contribution of each component as a discrete entity. The formulation is implemented numerically through the Fortran User Element subroutine UEL of the general purpose software Abaqus. This novel approach that we call “dual cohesive element” is suitable for synthetic macro fibre-reinforced concrete. It can represent the overall structural behaviour with a coarse discretisation which makes it particularly fast and efficient. Once a certain fibre distribution across the crack is postulated, single fibre pull-out test results can be used to simulate the load-displacement performance of the structure. This numerical method is validated experimentally and compared with single fibre pull-out tests and three point bending beam tests which proved its accuracy in predicting crack opening in Mode I. A mesh refinement study is also conducted and the structural response obtained from the numerical simulation show mesh independent results. There is good agreement between experimental and simulated results even with a coarse mesh representation. The results highlight the intimate relationship between single fibre pull-out test and the behaviour of fibre reinforced concrete with multiple fibres.