1,721,093 research outputs found
Study of masonry structures in civil engineering using the discrete element methods : benefits of the Non Smooth Contact Dynamics method
No full textLa maçonnerie est une technique de construction très ancienne qui est toujours d'utilisation très répandue sous toutes les latitudes. Elle fait appel à deux éléments essentiels : des blocs et des joints, qui peuvent être éventuellement remplis de mortier. Le matériau obtenu peut être considéré comme continu ou discontinu, selon les propriétés relatives des blocs et des joints. Les blocs sont souvent en pierre, en brique crue ou cuite. Les mortiers sont généralement à base de chaux, de ciment ou d'un mélange de ces deux composants. Depuis l'apparition du béton au XIX° siècle, les calculs se sont concentrés sur des approches continues, et les techniques de conception des maçonneries ont peu bénéficié des avancées scientifiques, et du développement d'outils de calcul largement utilisés dans les bureaux d'études. Corrélativement à cette évolution, la maçonnerie a perdu des parts de marché de la construction, et les méthodes et moyens mis en œuvre pour la conception d'ouvrages en maçonnerie n'ont pas été suffisamment modernisés. Dans ce contexte, le présent travail a pour ambition de contribuer au calcul de structures maçonnées, considérées comme des structures discontinues, avec l'objectif de servir au monde de l'entreprise et de l'architecture.L'échelle d'étude de la structure ou du matériau : comportement général de l'ensemble bâti, comportement d'un panneau de maçonnerie, comportement de l'interface mortier - bloc, ou des contacts blocs-blocs dans le cas de maçonnerie à joints vifs, conduit à l'utilisation de divers cadres théoriques, et méthodes analytiques ou numériques correspondantes. Après une analyse des avantages et inconvénients de diverses méthodes disponibles, numériques ou graphiques, dans le domaine de la mécanique et de l'architecture (stéréotomie), nous présentons en détail la méthode Non Smooth Contact Dynamics. Cette méthode, initiée à la fin du XX° siècle, par Jean-Jacques MOREAU et Michel JEAN, décrit de façon théorique, les conditions de mise en place des efforts de contact entre corps solides, déformables ou rigides, en 2D et 3D, en présence de chocs, et en présence de grands déplacements, ou rotations. Les conditions de non interpénétration entre corps sont régies par un formalisme spécialement développé dans le cadre de l'analyse convexe. Nous avons retenu ce cadre théorique, et utilisé une chaine logicielle développée sur ses bases, pour modéliser des structures réalistes, c'est-à-dire tridimensionnelles, soumises à des chargements dynamiques, et qui sont modernes, dans la mesure où elles intègrent une géométrie complexe, performante (économie de matière et esthétique) et la mise en œuvre d'une précontrainte, avec prise en compte de son phasage.L'exemple de la structure de l'escalier de Ridolfi est utilisé comme support à l'examen de divers paramètres d'optimisation du calcul réalisé avec la plateforme ouverte LMGC90, permettant à l'utilisateur de maîtriser en détail les diverses phases du calcul non-linéaire conduit. Les paramètres du calcul dont nous avons testé l'influence sont : le pas de temps, le critère de convergence, le nombre d'itérations gérées par l'algorithme de Gauss-Seidel, le critère de rétrécissement, le coefficient de frottement entre blocs, et l'intensité de la précontrainte mise en place par post tension dans les câbles. L'expérimentation conduite sur un modèle physique en vraie grandeur, est reconstituée, dans ses différentes phases, sur maquette numérique, et la pertinence des résultats obtenus par simulation est discutée.Les travaux ont été réalisés au Laboratoire de Mécanique et Génie Civil de l'Université Montpellier II et du CNRS, et au Laboratoire de Génie de l'Environnement Industriel de l'Ecole des Mines d'Alès. Leur financement a été assuré par le Ministère de l'Education et de la Formation du Vietnam, ainsi que par ARMINES.Although it is an old construction technique, masonry is still world wide spread nowadays. It uses two main components: blocks and joints, which can be filled with mortar. The resulting material can be considered as continuous or discontinuous, according to the relative performances of the blocks and joints. The blocks are often made of stone, raw earth or brick. The mortars generally incorporate lime or cement or a mixture of those components. Since the discovery of modern concrete during the XIXth century, calculations have been performed in the framework of continuous methods, and the masonry design technics have not fully benefited from the scientific breakthrough, nor from the development of calculation tools used in design offices. Following this evolution, masonry lost some ground in the construction field, and methods and means used for the design of buildings have not been improved enough. In this context, the present work aims at contributing to the calculation of masonry structures, considered as discontinuous structures, with the ultimate goal to be of some use in the field of industry and architecture.The structure or material study scale: general behavior of the building, behavior of a masonry panel, or behavior of the bonding between the blocks and the mortar, or the block-block contacts for dry friction masonry, leads to the use of several theoretical frameworks, and associated analytical or numerical methods. After an analysis of the pros and cons of the different available methods, in the fields of mechanics and architecture (stereotomy), we will present in detail the Non Smooth Contact Dynamics method. This method, initiated at the end of the XXth century, by Jean-Jacques MOREAU et Michel JEAN, describes theoretically, the conditions of the development of contact forces between solids, whether able to support strains or rigid, in 2D or 3D, under the effects of shocks, large displacements or rotations. The conditions of no overlapping between the bodies are described by equations developed using the convex analysis concepts. We chose this theoretical framework, and used the software platform developed on these concepts, for modeling realistic structures that are modern, because they allow to take into account 3D structures with complex and efficient geometries (aesthetic point of view, economy of material), subjected to dynamical loads, and including the sequential set-up of pre-stressing technics.The example of the Ridolfi stair case is used as a support for the examination of several optimization parameters for the calculation performed on the LMGC90 open software, allowing the modeler to supervise in detail several steps of the performed non-linear calculations. The calculation parameters of which we have tested the influence are: the time step, convergence criterion, the iteration number considered in the Gauss-Siedel algorithm, the shrinkage criterion, the friction coefficient between blocks, and the pre-stressing strain applied in the post tension cables. The experiment carried out on a real size physical model is numerically simulated, and the consistency of the computed results is discussed.The work was carried out in the Mechanics and Civil Engineering Laboratory of the University of Montpellier II and the CNRS (French National Scientific Research Agency), and the Laboratory of Industrial Environment Engineering of Alès School of Mines. The funding was provided by the Ministry of Education and Training of Vietnam, and ARMINES
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Combination of statistical and mechanical methods for collapse risk assessment of underground masonry structures : Case study of cover stream tunnels in the Cévenol mining heritage
No full textLes ruisseaux couverts sont d’anciens tunnels maçonnés à vocation hydraulique, recouverts de stériles miniers au-dessus desquels différentes infrastructures ont été construites. De récents effondrements posent aujourd’hui la problématique de l’estimation du risque d’effondrement de ces ouvrages. Dans cette thèse, nous avons tenté de proposer une méthodologie permettant de répondre à cette problématique. Du fait de l’intensité du phénomène étudié, l’étude s’est concentrée sur la détermination de la probabilité d’occurrence et sur les enjeux.L’utilisation de la méthode multicritère AHP a permis de proposer une note de risque à partir des enjeux et des désordres en présence. Du fait de l’incapacité du modèle à estimer rétroactivement les effondrements relevés sur 28 ouvrages, l’étude s’est par la suite concentrée sur l’estimation de la probabilité d’occurrence des effondrements.Une analyse statistique a permis d’estimer que les effondrements rencontrés dans ces ouvrages étaient liés à l’effondrement des piédroits (83% des cas) et à l’effondrement de la sortie des ouvrages (17% des cas). L’utilisation de la méthode de la régression logistique a permis, à partir de paramètres géométriques et de désordres observés, d’estimer rétroactivement et avec un F1-score moyen de 84% la probabilité d’occurrence de ces deux types d’effondrement.Afin de prendre en compte la dégradation des propriétés mécaniques des maçonneries, nous avons proposé un méta-modèle d’estimation du coefficient de sécurité des piédroits à partir de modèles numériques. L’approche a été évaluée rétroactivement et a permis d’obtenir un F1-score de 82%.Une combinaison des approches a ensuite été utilisée pour estimer le risque effondrement de 28 ouvrages découpés virtuellement en 180 tronçons. La méthodologie développée et les résultats obtenus pourront permettre de prioriser des actions préventives (réparations d’ouvrages, sécurisations de zones potentielles d’effondrement et mise en sécurité des personnes).Covered stream tunnels are old masonry hydraulic tunnels, covered with tailings, over which various infrastructures were constructed. Recent and unforeseen collapses have raised the issue of the lack of knowledge on the risk assessment of these tunnel collapses. In this thesis, we have proposed a methodology to tackle such an issue. Because of the intensity of the phenomenon, the study focused on determining the probability of occurrence of this identified hazard and the stake value.The application of the multi-criteria analysis enabled to propose a risk-scoring model based on the issues and the disorders involved. As the model fails to retroactively predict the collapses observed on 28 structures, the study then focused on estimating the probability of the collapse occurrence.A statistical analysis has enabled us to estimate that the collapses encountered in these tunnels were related to the collapse of the sidewalls (83% of the total number of collapses) and the tunnel exit collapse (17% of the total number of collapses). The application of the logistic regression method, by using the geometrical features and the disorders observed in-situ, enabled to evaluate retroactively, with an average F1-score of 84 %, the probability of occurrence of these two types of collapses.In order to consider the degradation of the mechanical properties of masonry, we have proposed a meta-model that could estimate a safety coefficient of the sidewalls from numerical models. The approach was evaluated retroactively and resulted in an F1 score of 82%.All of these approaches were then aggregated and used to assess the collapse risk of 28 underground tunnels virtually divided into 180 sections. The methodology developed and the results obtained will enable us to prioritize preventive actions (structural repairs, securing potential areas of collapse and securing people)
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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