Laurent Daudeville

Compression triaxial behavior of concrete: the role of the mesostructure by analysis of X-ray tomographic images

This paper is intended to assess the mesostructural damage mechanisms of concrete under hydrostatic and triaxial loadings. Such a study is possible thanks to two state-of-the-art laboratory instruments: a high-pressure triaxial press, and an X-ray computed tomography instrument. The laboratory protocol consists of scanning the concrete prior to the initial loading and after each cycle. An analysis of the resulting images indicates that under high hydrostatic loading, significant damage is visible in cement paste at the mesoscopic scale. For two triaxial tests conducted at 50 and 650 MPa of confining pressure, results reveal major differences in both damage and failure mechanisms. At the lower pressure, shear loading creates a localised failure mechanism characterised by sliding on an inclined plane, whereas at the higher pressure, the strain and damage mode are much more homogeneous with a failure localisation after unloading. Cet article a pour objectif d’estimer les mécanismes d’endommagement du béton présents à l’échelle mésoscopique sous chargements hydrostatique et triaxial. Une telle étude est possible grâce à deux instruments de laboratoire: une presse triaxiale de grande capacité, et un tomographe à rayons X. Le protocole de réalisation des essais consiste à scanner le béton à l’état vierge et après chaque cycle. L’analyse des images obtenues indique que sous fort chargement hydrostatique, l’endommagement est visible dans la pâte de ciment à l’échelle mésoscopique. Pour deux essais triaxiaux, réalisés à 50 et 650 MPa de pression de confinement, les résultats montrent des mécanismes d’endommagement et de rupture très différents. À basse pression, le cisaillement provoque un mécanisme de rupture qui apparait sous la forme d’un plan de glissement incliné. À forte pression, la déformation et le mode d’endommagement sont beaucoup plus homogènes avec néanmoins une localisation de la rupture lors de la décharge.

A discrete element/shell finite element coupling for simulating impacts on reinforced concrete structures

The efficiency of the discrete element method for studying the fracture of heterogeneous media has been demonstrated, but it is limited by the size of the computational model. A coupling between the discrete element and the finite element methods is proposed to handle the simulation of impacts on large structures. The structure is split into two subdomains in each of which the method is adapted to the behaviour of the structure under impact. The DEM takes naturally into account the discontinuities and is used to model the media in the impact zone. The remaining structure is modelled by the FEM. We propose an extension of the coupling procedure to connect the Discrete Element model to shell-type Finite Elements. The efficiency of the coupling method is tested and validated.

Une méthode simplifiée pour l'analyse du délaminage auprès d'un bord droit

ABSTRACT A simplified method based upon damage mechanics for the delamination analysis of composites is presented. In the neighbourhood of a quasi-straight edge of a laminated structure, damage is taken concentrated on the interface between layers. The finite element code EDA, acting as a post-processor of an elastic laminate shell computation, allows the prediction of delamination onset and propagation. Numerical simulations of delamination are given and compared with experimental results from literature.

Traditional Timber-Framed Infill Structure Experimentation with Four Scales Analysis (To Connection from a House Scale)

The aim of this paper is to contribute toward a better understanding of the seismic behavior of timber-framed infill structure. For this purpose, the results of a multi-scale experimental program are presented. The paper presents also the feasibility to use a DIC analyse on a full-scale of a house tested on a shake table.

Numerical analysis on seismic resistance of a two-story timber-framed structure with stone and earth infill

ABSTRACT Due to their seismic resistance, traditional timber-framed structures with masonry infill suffered little damage during recent earthquakes. Moreover, timber-framed structures can be built with reduced costs thanks to the use of locally available materials such as wood, stone, and earth. Based on an experimentally validated numerical simulation for a one-story house, the seismic resistance of a similar two-story house is investigated. A simplified Finite Element Model with linear and nonlinear truss elements is proposed to analyze the seismic resistance of a two-story building. Nonlinear hysteresis constitutive laws are defined only for two majorcomponents of the structure which are assumed to be representative of the global structure behavior: diagonal X-crosses (concentrating the interaction with the infill material) and steel strip connections. These kinds of structures have been overlooked due to a lack of knowledge of their potential behavior in seismic prone area and a lack of building codes and standards for their own design. To promote them, a failure criterion, that might easily be used in engineering studies, is required. This article proposes a simple criterion based on Eurocode 8 to quantify the seismic resistance of one- and two-story houses. The simulation shows that, even in case of high intensity ground motion, the two-story building should not be collapsed. This study may help at designing two-story timber-framed structures in seismic prone areas for (re)construction projects.

Coupled Discrete Element/Finite Element Method for the Analysis of Large Reinforced Concrete Structures Submitted to an Impact

The efficiency of the discrete element method for studying the fracture of heterogeneous media has been demonstrated, but it is limited by the size of the computational model. A coupling between the discrete elements (DEM) and the finite elements (FEM) methods is proposed to handle the simulation of impacts on large structures. The structure is split into two subdomains in each of which the method is adapted to the behavior of the structure under impact. The DEM takes naturally into account the discontinuities and is used to model the media in the impact zone. The remaining structure is modeled by the FEM. We propose an adaptation of the coupling procedure to connect Discrete Element model to shell-type Finite Elements. Finally, the efficiency of this approach is shown on the simulation of a reinforced concrete slab impacted by a tubular impactor.