Guillermo Etse

Constitutive Modeling and Discontinuous Bifurcation Assessment in Unsaturated Soils

In this work an elastoplastic constitutive theory for unsaturated soils is presented. The proposed material model is formulated in the general framework of the theory of porous media and of the flow theory of plasticity. The model is based on an extension of the well-known MRS Lade model whereby the suction and the effective stress tensor are introduced as additional independent and dependent stress components, respectively. Consequently the cap and cone yield conditions of the MRS Lade model both in hardening and softening as well as the internal evolution laws in these regimes are redefined to include the dependency on the suction. The paper illustrates the predictive capability of the extended MRS Lade model for partially saturated soils. Finally, the condition for discontinuous bifurcation in elastoplastic partially saturated porous media as well as the localized failure predictions of the proposed material formulation for different suctions and stress states are also analyzed and discussed.

Performance Dependent Failure Criterion for Normal- and High-Strength Concretes

A new approach to describe the maximum strength criterion of concretes with different strength capacities is formulated. The proposed failure criterion incorporates the so-called “performance parameter” ( βP ) that controls the dependence of the maximum strength on the concrete quality. To assure the feasibility of the solution procedure for any possible set of known data, different methods are proposed to determine βP according to the available material data. The performance dependent strength criterion presented in this work is expressed in terms of the Haigh Westergaard stress coordinates and as a function of four material parameters that fully define the compressive and tensile meridians of the failure criterion. The variation of the shear strength between these two meridians follows an earlier elliptic interpolation. The proposal includes approximating functions that define the dependence of the above mentioned four material parameters on the two fundamental mechanical properties of concrete: the uni...

Advanced Numerical Models for the Analysis of Sustainable FRC Structures

This chapter introduces some of the relevant modelling approaches that are being used to simulate the behaviour of cementitious materials reinforced with discrete fibres. The major part of these approaches were originally proposed for modelling non-fibrous reinforced cement based materials‚ therefore the main focus herein given is related to the aspects how fibre reinforcement mechanisms have been considered. These approaches were grouped in two classes‚ one where fibres are explicitly considered in the finite element mesh (FEMesh)‚ herein designated as Discrete Fibre Reinforcement Approaches (DFRAs). The other class is designated by smeared fibre reinforcement approaches (SFRAs)‚ where fibres are not part of the FEMesh and their contribution is basically considered attributing a constitutive law to the FRC that simulates the fibre reinforcement mechanisms in terms of the fracture modes of this composite material.

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.