A new modeling Strategy for the behavior of walls under dynamic loading

International audienceA new simplified modelling strategy to simulate the non‐linear behaviour of reinforced concrete shear walls under dynamic loading is presented. The equivalent reinforced concrete (ERC) model is derived from the framework method and uses lattice meshes for concrete and reinforcement bars and uniaxial constitutive laws based on continuum damage mechanics and plasticity. Results show the capacity of the model to analyse structures having different slenderness and boundary conditions. For low reinforcement ratios however, results are sensitive to the angle formed by the diagonals of the concrete lattice and the horizontal bars. The method is compared with the shear multi‐layered beam model that uses Timoshenko multi‐layered 2D beam elements and biaxial constitutive laws. Comparisons for both models with experimental results of two research programs (one organized by NUPEC and the other by COGEMA and EDF) are provided. ERC is a simplified method that intends to save computer time and allows parametrical studies

A macro-element to simulate 3D soil-structure interaction considering plasticity and uplift

International audienceIn structural engineering, soil–structure interaction (SSI) is an important phenomenon that has to be taken into account. This paper presents a 3D non-linear interface element able to compute SSI based on the “macro-element” concept. The particularity of the macro-element lies in the fact that the movement of the foundation is entirely described by a system of generalised variables (forces and displacements) defined at the foundation centre. The non-linear behaviour of the soil and the uplift mechanism of the foundation are reproduced using the plasticity theory. The failure surface is defined using an adequate overturning mechanism. Coupling of the different mechanisms is straight forward following the theory of multi-mechanisms. The macro-element is able to simulate the 3D behaviour of a rigid shallow foundation of circular, rectangular or strip shape, submitted to cyclic loadings. It is implemented into FEDEASLab, a finite element MATLAB toolbox. Comparisons with experimental results under cyclic loadings show the performance of the approach

A Model to Forecast the Response of Concrete under Severe Loadings the μ Damage Model

AbstractAmong the “theories” applied to model concrete behavior, damage mechanics has proven to be efficient. One of the first models for concrete introduced within such a framework is Mazars’ damage model. A new formulation of such a model, called the “μ model”, is proposed herein for the purpose of 3D cyclic and dynamic loading, based on a coupling of elasticity and damage within an isotropic formulation. Unilateral behavior (i.e. the opening and closure of cracks) is introduced by the use of two thermodynamic variables. A threshold surface is then associated with each of these variables and strain rate acts on the initial threshold. Applications are presented on plain or reinforced concrete elements subjected to various loading (uni- and multi-axial, cyclic, dynamic). A comparison with experimental results demonstrates the effectiveness of the various selected options

Analyse sismique du comportement d'une structure de 7 étages à échelle 1 en béton armé: benchmark international NEES

Dans le cadre d'un partenariat entre le consortium Américain NEESinc, l'université de Californie de San Diego (UCSD) et l'association du ciment Portland (PCA) of Skokie, IL., des essais sur table sismique d'une structure de grande hauteur soumise à des séismes d'intensités croissantes ont été réalisés. Il s'agit d'une structure de 7 étages à échelle 1 en béton armé composée de deux murs perpendiculaires. Un benchmark international a ensuite été réalisé sans que les organisateurs ne dévoilent les résultats expérimentaux (blind test). La modélisation présentée dans cet article a consisté en une étude dynamique non linéaire par une discrétisation de la structure à l'aide d'éléments poutres multifibres Timoshenko, et l'utilisation de lois d'endommagement pour le béton. On montre ici, d'une manière quantitative, que la modélisation effectuée permet de décrire de manière assez précise le comportement expérimental de la structure, et d'une manière qualitative que le modèle donne de bons résultats concernant la distribution de l'endommagement

Full Scale Dynamic Response of a RC Building under Weak Seismic Motions Using Earthquake Recordings, Ambient Vibrations and Modelling

International audienceIn countries with a moderate seismic hazard, the classical methods developed for strong motion prone countries to estimate the seismic behaviour and subsequent vulnerability of existing buildings are often inadequate and not financially realistic. The main goals of this paper are to show how the modal analysis can contribute to the understanding of the seismic building response and the good relevancy of a modal model based on ambient vibrations for estimating the structural deformation under moderate earthquakes. We describe the application of an enhanced modal analysis technique (Frequency Domain Decomposition) to process ambient vibration recordings taken at the Grenoble City Hall building (France). The frequencies of ambient vibrations are compared with those of weak earthquakes recorded by the French permanent accelerometric network (RAP) that was installed to monitor the building. The frequency variations of the building under moderate earthquakes are shown to be slight (~2%) and therefore ambient vibration frequencies are relevant over the elastic domain of the building. The modal parameters extracted from ambient vibrations are then used to determine the 1D lumped-mass model in order to reproduce the inter-storey drift under weak earthquakes and to fix a 3D numerical model that could be used for strong earthquakes. The correlation coefficients between data and synthetic motion are close to 80% and 90% in horizontal directions, for the 1D and 3D modelling, respectively

Modèle simplifié 3D de l'interaction sol structure : application au génie parasismique

Dans le domaine du génie parasismique, l'interaction du sol avec la structure (ISS) est un phénomène important à considérer pour espérer rendre compte du comportement réel d'une structure et donc évaluer sa vulnérabilité. Ce travail présente la construction d'un élément d'interface 3D modélisant une fondation superficielle circulaire reposant sur un massif de sol semi infini et permettant de prendre en compte l'ISS en considérant la plasticité du sol et le décollement de la fondation. Basé sur la méthode des macro-éléments, cet élément permet de travailler en variables globales (forces et déplacements) et permet ainsi de simplifier le modèle et d'obtenir des temps de calculs très réduits. Il est implémenté dans FedeasLab, un code élément finis développé dans Matlab. Après une description mathématique, des comparaisons avec des résultats expérimentaux d'une fondation soumise à des chargements statiques monotones et cycliques montrent le bon fonctionnement du macro élément 3D d'ISS

Modélisation de structures en béton armé avec des éléments poutres multifibres

International audienceOn présente dans cette étude la modélisation du comportement de structures en béton armé en utilisant des éléments poutres multifibres. Les modèles du comportement utilisés associent plasticité pour les aciers et endommagement pour le béton. Les structures étudiées sont un poteau soumis à un chargement cyclique 3D, testé au laboratoire ELSA d'Ispra et un bâtiment à deux murs contreventés, testé à la table sismique du laboratoire LNEC à Lisbonne

Methodology and numerical strategy for forecasting the leakage rate evolution of nuclear reactor buildings inner containments

The containment building represents the third and last protection barrier of nuclear reactors buildings (NRB). Yet ageing mechanisms of prestressed concrete could strongly affect the tightness capacity of the inner containment of a double-wall reactor building over time. That is a major issue considering the long-term operation and the potential life extension of NRBs while ensuring safety and regulatory requirements. Considering the size of those structures and the complexity of all interacting phenomena (such as drying, creep, shrinkage and cracking), it is very difficult from a computational perspective to build an industrial and operational tool modeling efficiently all the strong couplings occurring at different scales. In that context, a simple yet physically representative chained weakly-coupled strategy based on a macro-element discretization is implemented and applied to the VeRCoRs mock-up (scale 1:3). The proposed methodology adapts to feedback and data collected with time. It enables operators to take into account variabilities and uncertainties of main parameters in order to quantify their impact on the total leakage rate, to manually introduce defects coming from visual inspections and to preempt and optimize leak mitigation actions in order to avoid outage extensions and associated losses of income

Modèle cyclique de béton confiné par TFC pour poteaux circulaires en béton armé

International audienceIn structural engineering, the seismic vulnerability reduction of existing structures is a crucial issue. External reinforcement using Fiber Reinforced Polymer (FRP) is an interesting tool in order to fulfill this aim.This paper presents a method to simulate the behavior of existing columns considering FRP reinforcement effect. It describes the construction of a 1D confined concrete behavior law suitable for monotonic and cycling loadings. The law is inspired on two well-known concrete laws, the first one based on damage mechanics theory (La Borderie concrete damage law) and the second one based on experimental studies (Eid & Paultre concrete monotonic law). Structures are discretized using multifiber beam elements. Validation of the approach is provided using experimental tests of RC columns under axial and flexural cyclic loading.En génie parasismique, la réduction de la vulnérabilité des structures existantes est un enjeux majeur. Le renforcement externe d'éléments par collage de Tissus de Fibre de Carbone (TFC) est une réponse intéressanteà cette problématique. Cet article présente la construction d'un modèle uniaxial de béton confiné adapté au cas des chargements monotones et cycliques. Ce modèle est fondé sur deux modèles bien connus, le premier basé sur la théorie de l'endommagement (La Borderie) et le second basé sur une série d'études expérimentales (Eid & Paultre). Le modèle est implanté dans un codé eléments finis multifibres. Une validation expérimentale de ce modèle est menée enétudiant le cas de poteaux en béton armé soumisà un chargement cyclique de flexion composée