Ludovic Jason

Benchmarks for the validation of a non local damage model

ABSTRACT The aim of this contribution is to present a series of organised benchmarks that helps at validating the robustness of the FE implementation of a constitutive relation, its pertinence with respect to experiments, and quantitative and qualitative comparisons of structural elements. It is applied to an isotropic damage model used for concrete, coupled with a non local gradient formulation to avoid a spurious description of strain localisation. After the elementary (uniaxial monotonic, cyclic or triaxial loading) and structural (three point bending tests) simulations, an industrial application is presented in the form of a representative structural volume of a containment building for French nuclear power plants.

Continuum damage modelling and some computational issues

ABSTRACT Continuum damage mechanics is a framework for describing the variations of the elastic properties of a material due to microstructural degradations. This paper presents the application of this theory to the modelling of concrete. Several constitutive relations are devised, including incremental, explicit, and non local damage models. A general framework for damage induced anisotropy is also presented. In the second part of this contribution, computational issues in damage mechanics related to iterative schemes and solution control in non linear computations are considered. The paper concludes with an example of 3D finite element computation of a reinforced concrete beam, as part of a benchmark initiated by Electricité de France.

Modelling strategies of prestressing tendons and reinforcement bars in concrete structures

This contribution presents an original approach to improve the modeling of steel rebars and prestressing tendons in concrete structures at a reduced cost. Classical 1D meshes and models typically used for civil engineering applications tend to provoke strain localization due to the geometrical singularity and are thus unable to reproduce local mechanical effects. Complete 3D models can be applied in some cases, however their accuracy at the local scale comes at the cost of engineering work on the meshes, especially for complex structures. The 1D-3D model presented in this contribution generates an equivalent volume for the steel bars, based on existing 1D models. Its 3D stiffness and stress state are computed, and then condensed on its interface with the concrete. The condensed degree of freedom are then linked to the surrounding concrete elements by kinematic relations. The presented approach is validated on different representative cases, and is able to predict the 3D effects of the bars and tendons at the local scale. In particular it provides the representativeness and mesh stability of a full 3D model, without the need for a complex mesh.

Damage mechanics applied to the seismic behavior of concrete structures

ABSTRACT The seismic behavior of reinforced concrete structures is generally evaluated through modal spectral approaches, based on linear elastic analysis. In the case of seismic reevaluation of existing structures using traditional methods, since the nonlinear behavior of materials is not taken into account, these techniques often lead to an overestimation of the needs in reinforcement. In this contribution, it is proposed to highlight how including nonlinearity in the mechanical behavior of concrete and steel can improve the seismic evaluation of RC structures. For this purpose, a pushover technique is applied on an office building. Contrary to a classical approach, the progression of the failure mode and the mechanical degradation can be obtained and used to accurately elaborate the best retrofitting strategy. Some improvements of the constitutive laws are nevertheless needed if the use of this type of approaches is to be extended to more complex structures. However, the maturity of most constitutive models is not enough to allow industrial applications.

Continuum damage modelling in geomechanics

Continuum damage mechanics is a framework for describing the variations of the elastic properties of a material due to microstructural degradations. This chapter presents the application of this theory to the modelling of concrete. Several constitutive relations are devised, including incremental, explicit, and non local damage models. A general framework for damage induced anisotropy is also presented. Coupled damage and plasticity modelling is discussed. Finally, the issue of the experimental determination of the internal length in non local models is tackled.