Figure 2 - uploaded by Estelle Hervé-Secourgeon
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14 -Modélisation usuelle par des éléments finis de plaques d'une zone de structure incluant une jonction voile-plancher Les éléments de structure (voile, plancher) sont donc supposés être prolongés jusqu'à l'axe de la jonction par des éléments plaques ou coques d'une souplesse égale à celle du plancher. Or la jonction est nécessairement plus rigide qu'une simple plaque d'épaisseur égale à celle du voile ou de la dalle. L'application de la théorie des plaques dans ces zones, en rouge sur la 14, n'est donc ni légitime ni réaliste d'un point de vue de la rigidité. Par ailleurs, dans les modélisations plaques usuelles, l'erreur est souvent accentuée par l'application des chargements répartis (poids propres et masses réparties) à l'intégralité des éléments constituant le plancher, y compris au-delà du nu du voile qui n'est pas matérialisé dans le maillage. De même, l'évaluation des besoins en ferraillage se fait généralement en exploitant les résultats obtenus jusqu'à l'axe de la jonction et no en s'arrêtant au nu des voiles. De façon à évaluer l'impact de l'erreur commise en appliquant la modélisation plaques usuelle, on considère le cas théorique et simple d'une poutre bi-encastrée de longueur í µí± soumise à un chargement répartie de valeur í µí± ou à une charge ponctuelle í µí°¹.
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Dans le cadre des réévaluations de la sûreté sismique des installations nucléaires, EDF est amené à caractériser la tenue des structures de bâtiments nucléaires en béton armé et des équipements qu’elles supportent. Les études d’ingénierie s’appuient sur la simulation numérique. Pour améliorer les capacités de ces calculs, EDF a lancé un programme d...
Citations
... In this paper, the specific case of the wall-slab connection is studied. A simple approach based on kinematic operators between plate elements and eight nodes prismatic elements is presented (Hervé-Secourgeon, 2020). For the other general cases, the Arlequin method can be considered, (e.g. ...
... The validation of this elastic model for wall-slab connections has been carried out through a systematic comparison between the proposed methodology, the usual practice based only on plates and a reference brick element model validated by means of physical experiments on large scale models. This validation is demonstrated in (Hervé-Secourgeon, 2020) and (Hervé-Secourgeon, et al., 2019) and summarized in Fig. 15, Fig. 16 and Table 4. One can see that the proposed method is almost systematically closer (for 5 cases out of 7) to the reference than the current practice in terms of the macroscopic stiffness measurement (ratio between the applied force or moment and the displacement or rotation observed at the application point of the force). ...
... Nevertheless, the impact on the local modes (bending modes of the individual walls or slabs for instance) is more significant, with slightly higher frequencies computed with the hybrid model. Two sources can be identified that account for these differences: (Hervé-Secourgeon, 2020). ...
The design of nuclear civil structures based on rules in European standards makes extensive use of the Finite Element Method (FEM). The size and complexity of the models are continuously increasing. Lately, the post-processing of the FEM results has centered the engineers’ contribution on analyzing the reinforcement density produced using automated methods dealing with shell or plate models, which often leads to excessive plate use even in D-regions (discontinuity or disturbance region). This practice is particularly problematic for nuclear structures, which exhibit a large set of massive parts due to radiation protection requirements in many areas such as the reactor pit, the raft, or the containment gusset. Furthermore, these substructures are generally not well aligned with thin structural elements (such as slabs and walls) due to heavy equipment, piping, and HVAC (heating, ventilation, and air conditioning) constraints. This is contrary to what should be done to achieve the best engineering design.
To address these issues, an overall modeling and post-processing approach is proposed herein. The objective is to enhance the implementation of the finite element model and the post-processing phase to improve the quality of the modeling and reinforcement of B (non-disturbed region) and D regions without significantly impacting the time needed for the design.
A second objective of the proposed methods is to improve the constructability of reinforced concrete nuclear structures. Indeed, the current modeling approach, which often misuses shell elements, often leads to a significant overestimation of the required reinforcement density and consequently complicates the fabrication of the reinforced concrete structures.
To illustrate the approach used here, an example based on a building typical of a nuclear structure is presented. The distinct benefits of both the overall modeling and the reinforcement post-processing are highlighted. This approach exhibits a saving of nearly 25% on the bending reinforcement sections of the outer walls compared to a practice that doesn’t account for the improvements presented in the paper. Moreover, it reduces the maximum values of reinforcement due to bending of a plate by almost 40% without changing the reinforcement calculation process. It also provides a smoothing method of the reinforcement ratio fringes based on energy conservation. The method is automated and replaces the common, time-consuming practice of averaging the reinforcement ratios for arbitrary defined sets of finite elements.
