Constitutive microplane and interface laws for multiscale analysis of steel fiber concrete

Non-linear failure behavior of Fiber Reinforced Concrete (FRC) is analyzed and modeled by means of two different approaches. On the one hand a microplane theory based on the continuum (or smeared-crack) approach is formulated while, on the other hand, an interface model based on the discrete crack approach is also considered. The predictions of these two model approaches are comparatively evaluated when brittle and ductile failure modes of FRC components are considered at the macro and mesoscopic levels of observation. To more objectively compare the predictive capabilities of the discontinuum and continuum model approaches similar constitutive considerations are taken into account in both model formulations to describe key mechanisms of FRC failure behavior. The well-known "Mixture Theory" is considered to describe the fiber-to-concrete interactions in terms of fiber debonding and dowel effects. As failure criterion, defining the onset of cracking, a second order hyperbola is considered which simulates the interaction between maximum shear and normal stresses of both microplane and interface interaction. After describing the features of both constitutive models, this work focuses on numerical analysis of FRC failure behavior. The results in this work clearly demonstrate the advantages and shortcomings of both model approaches for FRC failure behavior analyses while clearly show the relevant properties of the mechanical responses of this composite material during ductile and brittle failure modes.