Some Aspects of Formation of Cracks in FRC with Main Reinforcement

In this paper the response of fibre reinforced concrete with main reinforcement in pure tension is considered. Test results are presented showing three distinct regimes: a regime of linear elasticity, a regime of yielding at approximately constant stress, and finally, a regime of strain hardening. A simple model of the response of a tension member with main reinforcement and a partially opened crack is presented, and the influence of different shapes of the crack opening relation is studied. The case of a parabolic crack opening relation defines a brittleness number that describes the transition from discrete cracking to multiple cracking. It is shown, that if the crack opening relation is assumed to consist of a brittle contribution from the cement paste, and a more ductile contribution from the pull-out of the fibres, a plastic regime will be present in the tensile response. The fracture process is described from the uncracked state and formation of the first crack til the final stage where a large number of cracks have developed and the failure load is reached. The model is compared with experiments, and reasonable agreement is achieved.