Couplage numérique et expérimental pour l’évaluation probabiliste des structures bois sous chargement sismique

This paper presents a two-step probabilistic approach to deal with problems involving high-dimensional input parameter spaces. Firstly, the effective stochastic dimension is identified using a screening method. The most important parameters are then modelled as random variables and the others are represented by their mean values. Then, the variability of the model response is evaluated by the decomposition method. This approach is used to assess the integrity of timber roofs of residential houses under seismic event. The seismic loading is modelled by real earthquake ground motion records representing the seismic hazard of the city of Le Moule in Guadeloupe. The variability of the damage accumulated in the structure is properly assessed by computing the statistical moments and the construction of the probability density. The results have shown that the uncertain parameters have significant effect on the variability of the damage accumulated in timber joints located on the bracing members. In addition, the damage variability and the PGA near-collapse are closely correlated. Finally, the probabilistic computation results have been used to construct fragility curves, which are very useful for the design of timber roof

Human Cytomegalovirus Entry into Dendritic Cells Occurs via a Macropinocytosis-Like Pathway in a pH-Independent and Cholesterol-Dependent Manner

Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that is able to infect fibroblastic, epithelial, endothelial and hematopoietic cells. Over the past ten years, several groups have provided direct evidence that dendritic cells (DCs) fully support the HCMV lytic cycle. We previously demonstrated that the C-type lectin dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) has a prominent role in the docking of HCMV on monocyte-derived DCs (MDDCs). The DC-SIGN/HCMV interaction was demonstrated to be a crucial and early event that substantially enhanced infection in trans, i.e., from one CMV-bearing cell to another non-infected cell (or trans-infection), and rendered susceptible cells fully permissive to HCMV infection. Nevertheless, nothing is yet known about how HCMV enters MDDCs. In this study, we demonstrated that VHL/E HCMV virions (an endothelio/dendrotropic strain) are first internalized into MDDCs by a macropinocytosis-like process in an actin- and cholesterol-dependent, but pH-independent, manner. We observed the accumulation of virions in large uncoated vesicles with endosomal features, and the virions remained as intact particles that retained infectious potential for several hours. This trans-infection property was specific to MDDCs because monocyte-derived macrophages or monocytes from the same donor were unable to allow the accumulation of and the subsequent transmission of the virus. Together, these data allowed us to delineate the early mechanisms of the internalization and entry of an endothelio/dendrotropic HCMV strain into human MDDCs and to propose that DCs can serve as a "Trojan horse" to convey CMV from entry sites to other locations that may favor the occurrence of either latency or acute infection

SFE method using Hermite polynomials: An approach for solving nonlinear mechanical problems with uncertain parameters

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SFE method using Hermite Polynomials: an approach for solving nonlinear problems with uncertain parameters

Abstract We propose a stochastic finite element method for nonlinear mechanical systems whose uncertain parameters can be modeled as random variables. This method is based on a Gaussian standardization of the problem and on an Hilbertian approximation of the nonlinear mechanical function using Hermite polynomials. The coefficients of the approximation are obtained using a cubic B-spline interpolation of the response function. It provides simple expressions of the response moments. Some of its possibilities are illustrated through four numerical examples concerning one linear problem and three nonlinear problems (elasto-plastic behaviors and contact problem) in which the random parameters are modeled as correlated lognormal random variables. The numerical results obtained attest the relevance of this approach

Évaluation probabiliste de la sécurité des ouvrages hydrauliques en remblai vis-à-vis du mécanisme de glissement par la méthode des éléments finis stochastiques

National audienceLes ouvrages hydrauliques en remblai (barrages et digues) sont des ouvrages particuliers dont la sécurité se doit d’être constamment assurée. La stabilité au glissement de ces ouvrages est traditionnellement évaluée dans l’ingénierie par des démarches déterministes à l’équilibre-limite faisant intervenir les méthodes des tranches. Cependant, des méthodes plus évoluées comme celle des éléments finis sont plus appropriées, notamment dans le cas de configurations complexes, ou de matériaux compressibles. De plus, les études de dangers de barrages demandent désormais d’évaluer des probabilités de rupture relatives à certains scénarios, ce qui n’est pas toujours aisé. Un travail de thèse a été proposé par IRSTEA afin de développer une démarche probabiliste permettant l’évaluation de la fiabilité structurale d’un ouvrage hydraulique en remblai par rapport au risque de glissement basée sur les données réelles d’un barrage d’étude. Elle propose dans un premier temps une modélisation probabiliste du champ de pressions interstitielles. La variabilité spatiale de la perméabilité des matériaux est modélisée par un champ aléatoire. Les résultats de cette modélisation montrent un bon accord avec les mesures d’auscultation réalisées sur l’ouvrage. Dans un second temps, le champ de pressions obtenu est utilisé comme donnée d’entrée dans un modèle mécanique de calcul du facteur de sécurité par la méthode de réduction de paramètres. Dans ce calcul, les paramètres de cisaillement – cohésion et angle de frottement – sont également représentés par des champs aléatoires de façon à prendre en compte leur variabilité spatiale. La probabilité de défaillance de l’ouvrage est finalement obtenue grâce à des simulations de Monte-Carlo

Probabilistic stability analysis of an earth dam by SFEM based on field data.

International audienceThis paper performs a probabilistic stability analysis for an existing earthfill dam using a Stochastic Finite Element Method (SFEM) and considering the spatial variability of soil properties based on field data. Previous works on probabilistic slope stability analysis are generally based on hypothetical data while using data from existing earth structures is not widespread. A probabilistic procedure based on field data is here implemented to analyze the stability of an existing embankment dam. The spatial variability of several soil properties is modeled from the geostatistical analysis of the available dataset of the dam studied. Random variables and random fields representing the variability of dam materials are integrated into an FE model by performing Monte Carlo simulations (MCS). This probabilistic analysis based on field data allowed to characterize the variability of the sliding safety factor for the case study of an existing dam

Analyse probabiliste des pressions interstitielles d'un barrage en terre par éléments finis stochastiques basée sur des données de terrain

International audienceKnowledge of pore water pressure in an earth dam is crucial for analysing its mechanical stability. In classical calculations of these pressures, great uncertainty exists regarding the permeability of the materials and the representation of their spatial variability. In this article, a probabilistic analysis of pore water pressures based on field data is performed to represent the permeability with a 2D random field established from statistical and geostatistical analyses. This random field is introduced in a model based on the Finite Element Method (FEM) and the influence of the spatial variability of permeability on pore water pressure is then studied using Monte-Carlo simulations (MCS)

Probabilité de défaillance d'un barrage de remblai par instabilité de talus et par surverse. Réponse au thème B

International audienceTwo mechanical models of different complexity – one using Limit Equilibrium Method (Geostudio software) and the other Finite Element Method (code Cast3M) – are developed to assess the probability of failure due to slope instability considering cohesion and friction angle as random variables. Two hydraulic conditions (steady-state and transient) are also tested for both mechanical models. Fragility curves for sliding failure mode but also overtopping failure mode are then computed and combined using the Common Cause Adjustment. In order to compute the global failure probability of the dam, the resulting fragility curve representing the structural behaviour is finally combined with water pool level probabilities. The latter are calculated considering available floods data and the hydraulic behaviour of the dam-reservoir system. This paper aims to compare several cases based on different methods and assumptions to show their potential influence on the final failure probability. In this simple geometry case, the probability of failure is not affected by the mechanical model. On the other hand, the assumptions made on hydraulic conditions have a great influence on the risk of failure. The authors finally highlight that the developed finite element model is able to use random fields instead of random variables

Reliability analysis of earth dams sliding mechanism by stochastic finite element method based on construction data

International audienceHydraulic works are risky civil engineering structures and deterministic methods are traditionally used to evaluate their stability. A complete probabilistic approach has been developed to evaluate the structural stability of earth dams based on construction data, involving the spatial variability of the hydraulic and mechanical properties of the dam as it was constructed

Analyse de fiabilité du mécanisme de glissement de barrages en remblai par la méthode des éléments finis stochastiques, basée sur des données de terrain

International audienceHydraulic works are risky civil engineering structures and deterministic methods are traditionally used to evaluate their stability. A complete probabilistic approach has been developed to evaluate the structural stability of earth dams based on construction data, involving the spatial variability of the hydraulic and mechanical properties of the dam as it was constructed