Jean-Marie Reynouard

An elasto-plastic damage model for plain concrete subjected to high temperatures

A computational model allowing for the thermo-mechanical analysis of concrete structures at high temperatures by means of the finite element method is presented. The degradation of a part of the mechanical properties due to temperature is given through a diffused thermal damage model. Further, the model includes transient creep interaction with localized mechanical damage due to cracking. A comparison is made between experimental tests performed by some authors on concrete specimens at high temperatures and the numerical results obtained from the model presented.

NONLINEAR ANALYSIS OF REINFORCED CONCRETE SHEAR WALL UNDER EARTHQUAKE LOADING

A constitutive model for predicting the cyclic response of reinforced concrete structures is proposed. The model adopts the concept of a smeared crack approach with orthogonal fixed cracks and assumes a plane stress condition. Predictions of the model are compared firstly with existing experimental data on shear walls which were tested under monotonic and cyclic loading. The same model is then used in the finite element analysis of a complete shear wall structure which was tested under a large number of cyclic load reversals due to earthquake loading at NUPECs Tadotsu Engineering Laboratory. Two different finite element approaches were used, namely a two-dimensional and a three-dimensional representation of the test specimen. The ability of the concrete model to -reproduce the most important characteristics of the dynamic behaviour of this type of structural element was evaluated by comparison with available experimental data. The numerical results showed good correlation between the predicted and the actual response, global as well as local response being reasonable close to the experimental one.

A simple shear wall model taking into account stiffness degradation

The damage undergone by reinforced concrete structures affects their modal characteristics. The study consists of constructing an original simplified model for a heavily reinforced shear wall relying on modal characteristic changes related to a damage increase. The elaboration of this simplified model is realised in several stages. The first stage is devoted to the inelastic finite element analysis of a shear wall which was tested under pseudo dynamic loading. Then, by applying a set of ideal excitations to the two-dimensional finite element modelling, the identification of the decrease of the fundamental frequency as a function of a damage variable is carried out. The third stage is concerned with constructing a new uniaxial dynamic model by introducing directly the expression of the decrease of the fundamental frequency into the equation of motion. Finally, the validity of the simplified modelling is assessed by comparing the numerical results obtained from the finite element analysis with those derived from the simplified analysis, for different types of seismic excitation.

Fluage tertiaire du béton en traction: Modélisation d'éprouvettes entaillées sous chargement de traction maintenu élevé

ABSTRACT During aging of concrete, the observation of cracking growth under loads corresponds to a recent pathology of the civil engineering works (bridge, dam, confinement building). An interaction mechanism between creep strains and damage appears under high level stresses and creates irreversible changes. Both strength and tertiary creep tests on notched specimens under direct tensile stresses are performed until failure by Carpinteri and al. (1997) and put in a prominent manner this interaction. This research is based on the knowledge of the creep process in its tertiary phase. It allows proposing a numerical model, which can reproduce the interaction mechanism considering the rate effect of loading.

Performance sismique des structures à murs banchés

ABSTRACT This article presents a research programme carried out around a test on a shaking table at LNEC Lisbon. The model (scaled 1/3) is representative of a cell of building with slightly reinforced concrete structural walls. In the first part, the presentation, the realisation and the analysis of the test are exposed, showing that the followed design philosophy is adequate. In the second part, two types of finite element modelling are presented (a refined and simplified one). They prove the know-how acquired in this field giving access to a reliable simulation of the phenomena and to a fine analysis of the local and global behaviour of the structure.

Inelastic seismic analysis of the SPEAR test building

ABSTRACT In this paper, it is presented the study of the inelastic seismic response of the 3-storey irregular SPEAR building, which was pseudodynamically tested under bi-directional seismic excitations at the ELSA Laboratory of the Joint Research Centre. In the proposed method, a 3D modeling is employed to capture the seismic response of the structure. Comparison of analytical and experimental results indicates that the effect of fixed end rotation due to bond-slip plays an important role and has to be adequately taken into account.

Modal pushover procedures for seismic evaluation of reinforced concrete structures: using new nonlinear single degree of freedom systems

This study performs a pushover procedure called Modified-UMRHA for seismic analysis of a reinforced concrete structure, based on the UMRHA (uncoupled modal response history analysis) procedure proposed by Chopra and Goel. The objective is to investigate three approaches for setting up nonlinear single degree of freedom systems drawn from modal pushover curves. These curves are obtained using a non-adaptive load pattern equal to the consistent mass matrix times the modal shape. These approaches are applied on the 14-storey Grenoble City Hall studied in the framework of the ARVISE French research program. The results obtained from the Modified-UMRHA using different proposed nonlinear single degree of freedom systems are compared with those from a rigorous nonlinear response history analysis. Cette étude présente une procédure de pushover nommée Modified-UMRHA pour l’analyse sismique des structures en béton armé, basée sur la procédure UMRHA proposée par Chopra et Goel. L’objectif est d’examiner trois approches se distinguant par la définition de systèmes non linéaires à un degré de liberté à partir des courbes de modal pushover. Ces courbes sont obtenues en utilisant un chargement non adaptatif égal à la matrice de masse consistante multipliée par la déformée modale. Ces approches sont appliquées sur un bâtiment de 14 étages, l’Hôtel de Ville de Grenoble étudié dans le cadre du programme de recherche ARVISE. Les résultats obtenus de la procédure Modified-UMRHA en utilisant différents systèmes non linéaires à un degré de liberté, sont comparés avec ceux issus de l’analyse non linéaire dynamique rigoureuse.

ARTIFICIAL ACCELEROGRAMS REPRESENTATIVE OF THE DAMAGE DISTRIBUTION ON A LOW-RISE SHEAR WALL

This study attempts to reproduce in an artificial way, at a given magnitude-distance couple, the statistical characteristics of damage caused by real accelerograms. The structure adopted is a low-rise shear wall, modelled as a nonlinear, one degree of freedom system with a degrading frequency as a function of a non-cumulative damage variable. Strong-motion records, contained in a large database, are characterised in terms of seismological and seismic parameters. Artificial accelerograms are generated from response spectra representative of real accelerograms belonging to different magnitude-distance zones. Although the mean damage is consistent, the low dispersion of damage caused by the artificial accelerograms with respect to that caused by the real accelerograms is highlighted. In order to reproduce the damage dispersion in addition to the mean damage, a generation method of representative artificial accelerograms is proposed. This method introduces the standard deviation drawn from attenuation relationships into a dispersion pre-process with respect to the regressed spectrum at a given magnitude-distance point. The method turns out to be capable of reproducing the statistical features of damage produced by real strong-motion records.

Mixed mode fracture of a higher order beam model in gradient-dependent plasticity

A higher-order shear-deformable beam model with gradient-dependent plasticity regularisation is presented in this work. The model takes into account a realistic non-linear variation of stresses and strains through the beam thickness. This enables mixed mode fracture analysis. Numerical results are presented for a multilayered beam. The discrete problem size is significantly reduced through this semi-local approach.

Modélisation du comportement mécanique du béton par une approche plastique endommageable

ABSTRACT This paper deals with an elastic-plastic model used to describe the concrete behavior. Coupling with damage theory can improve the phenomenological modeling. The aim of this paper is to put in a prominent manner the hypotheses and theoretical aspects which lead to the development of this approach.