The topic of structural dynamics involves an ample actuation field since the most of nature actions are time dependent. The analyses of structures in aerospace engineering, offshore engineering, civil engineering and others might be realized including the inertial effects since they have important role in reliability and safety of them. Due to the various nonlinearities that can be present in the dynamic analysis, the preview of the dynamic behavior of a structure can become a complex task. That analysis is generally executed using computational numeric algorithms improved for spatial and temporal discretization where computational requirements are excessive. Techniques based on element-by-element concept have gained recognition due to its increasing efficiency caused by the recent development of parallel computers. This work is focused on time integration algorithms for nonlinear dynamic problems formulated by the finite element approach. Besides, the considered algorithms have been prepared to be used, in the future, on parallel computational architectures. The main algorithms for nonlinear structural dynamics and alternatives of implementation of the element-by-element techniques are studied. The software MATLAB has been used for implementation of some algorithms, whose features are analyzed by examples. Some characteristics as computational cost, number of iterations and solutions quality are observed for nonlinear quasistatic and dynamic problems, adopting several spatial and temporal discretization levels. / A dinâmica de estruturas compreende uma vasta área de atuação visto que as ações da natureza são geralmente variáveis com o tempo. Análises de aeronaves, estruturas offshore, estruturas sujeitas a terremotos, entre outras, devem ser realizadas considerando também os efeitos inerciais, que têm papel importante na performance e segurança dessas estruturas. A análise do comportamento dinâmico dessas estruturas é bastante complexa em virtude das diversas não linearidades que podem estar presentes. Atualmente, essas análises são realizadas utilizando-se algoritmos numéricos computacionais para discretização espacial e temporal, exigindo, em geral, grandes esforços computacionais. Com o advento dos clusters de computadores na década de 90, o emprego de algoritmos numéricos paralelos utilizando a técnica elemento por elemento tem se difundido e se mostrado eficiente na solução desses problemas. Nesse contexto, este trabalho está direcionado ao estudo de algoritmos de integração no tempo para problemas de dinâmica não linear de estruturas pelo método dos elementos finitos, que possibilitem seu uso futuro em arquiteturas computacionais paralelas. Os principais algoritmos para dinâmica não linear de estruturas são revisados, assim como as alternativas de implementação através da utilização da técnica elemento por elemento. Em seguida, utilizando-se o programa computacional MATLAB, implementam-se alguns desses algoritmos e avaliam-se suas características através de exemplos ilustrativos. Observam-se, nesses exemplos, características como custo computacional, número de iterações e qualidade das respostas geradas para problemas quase estáticos e dinâmicos não lineares considerando-se diversos níveis de discretização espacial e temporal.

Modélisations simplifiées pour l’analyse du risque sismique de bâtiments en béton armé. Résumé de la thèse en français (1800 signes max.) : La thèse s’inscrit dans le cadre du projet MARS (Méthodes Avancées pour le Risque Sismique, EDF R&D). Elle concerne plus particulièrement certaines tâches sur le développement des méthodes simplifiées et robustes de calcul pour permettre la simulation intensive et table de la réponse sismique de bâtiments en béton armé. En effet, |’analyse de risque nécessite un très grand nombre de calculs pour tenir compte des incertitudes, tant sur le chargement (aléa sismique) que sur le comportement non linéaire des structures. Dans la première partie de ce travail, nous effectuerons une étude bibliographique sur les modèles de résolution sismique pour les bâtiments en béton armé. Cette étape va nous permettre de rassembler le maximum d’éléments nécessaires permettant de comprendre et d’identifier tous les paramètres, les avantages, les inconvénients et la limite d’utilisation de chaque procédure de calcul numérique par éléments finis. Dans la deuxième partie, on développe un macro-élément de poteau-poutre, associé â un modèle de comportement non linéaire afin de traduire la réponse de la structure sous les sollicitations sismiques. Des hypothèses cinématiques ont été adoptées pour limiter le nombre de degrés de liberté. La loi de comportement globale en cisaillement est décrite dans le cadre delà plasticité. Nous avons choisi un modèle à écrouissage cinématique pour prendre en compte la dissipation due à la fissuration. Les paramètres sont identifiés à partir de résultats expérimentaux ou bien pré-calculés par des analyses â une échelle locale (calculs 3D par éléments finis ou calcul simplifié type « Modified Compression Field Theory >>). Des analyses numériques ont été réalisées afin de valider le modèle proposé comparant à des essais expérimentaux disponibles dans la littérature. / This PhD is part of the MARS project (Advanced Methods for Seismic Risk, EDF R&D). It relates particularity to the development of simplified and robust calculation. The overall aim is to significantly reduce the intensive computation time without loosing a reliable simulation of the seismic response of reinforced concrete buildings methods. Seismic risk analysis requires a very large number of repeated calculations to account for uncertainties of both the loading (seismichazard) and the nonlinear behaviour of structures. ln the first part of this work, a bibliographic study on seismic resolution models for reinforced concrete buildings is provided. This step allows collecting the maximum of necessary elements to understand and identify all the parameters, advantages, disadvantages and limits of use of each finite element calculation method. In the second part, a macro—elements for beam—column joint associated to a nonlinear behavior to reflect the response to the structure under seismic loads ls developed. Kinematic assumptions have been adopted to limit the number of degrees of freedom. The law of global shear behavior is described in the context of plasticity. A model with kinematic hardening is chosen to account for the dissipation due to cracking. Model parameters are identified from experimental results or pre-calculated by analysis on a local scale vla 3D finite element calculation or the implied "Modihed Compression Field Theory Numerical analyses were performed to validate the proposed approach against experimental tests available in the literature.

This thesis deals with the nonlinear analysis of stability loss of flue gas pipe. This pipe is a part of desulphurization line. The thesis describes the creating of a simplified FEM model. It also describes the setting of the boundary conditions of the model for few loading cases. These cases differ by preference for one of the load as dominant. There are proposed several variants of stiffening by light ring stiffener. The work is finished by comparing the resistance to the stability loss of the reinforced variants and unreinforced model of flue gas pipe.