S. Vrech

Multiscale failure analysis of fiber reinforced concrete based on a discrete crack model

In this work the capabilities of an interface model to predict failure behavior of steel fiber reinforced cementitious composites (SFRCCs) are evaluated at both macro and mesoscale levels of observation. The interface model is based on a hyperbolic maximum strength criterion defined in terms of the normal and shear stress components acting on the joint plane. Pre-peak regime is considered linear elastic, while the post-peak behavior is formulated in terms of the fracture energy release under failure mode I and/or II. The well-known “Mixture Theory” is adopted for modeling the interactions between fibers and the surrounding cementitious composite. The effects of both the axial forces on the fibers induced by normal relative displacements, as well as the dowel action due to tangential relative displacements in the interfaces are considered in the formulation of the interaction mechanisms between fibers and cementitious composites. After describing the interface model, this work focuses on numerical analyses of SFRCC failure behavior. Firstly, the validation analysis of the interface model is performed at the constitutive level by comparing its numerical predictions against experimental results available in scientific literature. Then, the sensitivity of the interface theory for SFRCC regarding the variation of main parameters of the composite constituents is evaluated. Finally, the attention is focused on Finite Element (FE) analysis of SFRCC failure behavior at meso and macroscopic levels of observation. The results demonstrate the capabilities of the interface theory based on the Mixture Theory to reproduce the main features of failure behavior of SRFCC in terms of fiber content and involved fracture modes.

Constitutive Formulations for Concrete with Recycled Aggregates

In this Chapter, a thermodynamically consistent gradient model is proposed for natural aggregate concrete and then, modified to take into account the addition of different contents of recycled aggregates and its influence on concrete mechanical response. A particular and simple form of gradient-based plasticity is considered, where the state variables are the only ones of non-local character. After describing the material formulation for natural and recycled aggregate concretes, the model calibration is performed with experimental data taken from literature. A comprehensive numerical analysis is presented, where the effects of the recycled aggregate content on the performance of concrete in pre and post-peak behavior are evaluated and discussed, for different stress states. Finally, the ability of the model to capture the variation of mechanical response of concrete with different recycled aggregate contents is demonstrated for different mechanical tests.