Some Aspects of Formation of Cracks in FRC with Main Reinforcement

In this paper the response of fibre reinforced concrete (FRC) with main reinforcement in pure tension is considered. Test results are presented showing three distinct regimes: a regime og linear elasticity, a regime of yielding at approximately constant stress, and finally, a regime of strain hardening. a simple model is presented which takes into account the debonding between the reinforcement and the fiber reinforced matrix as well as the crack opening relation of the fiber reinforced matrix. The fracture process is described from the un-cracked state and formation of the first crack till the final stage where a large number of cracks have developed and the failure load is reached. The influence of different shapes of the crack opening relation is studied. It is shown, that if the crack opening relation is assumed to consist of a brittle contribution from the cement-based material, and a more ductile contribution from the fiber bridging, a plastic regime will be present in the tensile response. The case of a parabolic crack opening relation defines a brittleness number that describes the transition from formation of unstable discrete cracks to smaller cracks controlled by the softening behaviour of the fibre reinforced matrix. The model is compaired with experiments, and reasonable aggreement is achieved.