Na construção civil atual, existe uma tendência de crescimento da automatização do projeto, visando o desenvolvimento de soluções personalizadas a fim de fugir das indesejadas repetições arquitetônicas. Dentro desta tendência, as lajes planas protendidas proporcionam grande flexibilidade de layout, maior rapidez na execução da estrutura e diminuição do número de pilares, proporcionando ganhos de área útil. Um dos principais esquemas estruturais adotados para representar lajes planas protendidas é a laje lisa, com ou sem engrossamento na região dos pilares. As lajes lisas apresentam vantagens em relação às demais (nervuradas e outras), sobretudo do ponto de vista da facilidade de execução. Esta dissertação apresenta um modelo numérico para o cálculo de lajes planas lisas protendidas via Método dos Elementos Finitos.O elemento finito empregado, isoparamétrico com 8 nós, possui 5 graus de liberdade por nó: os 3 graus de liberdade referentes a teoria de Flexão de Placas de Reissner-Mindlin e os 2 graus de liberdade relativo ao Estado Plano de Tensões. A protensão é considerada através do Método de Equilíbrio de Cargas (criado por T. Y. Lin e utilizado por AALAMI (1990)), que consiste na transformação dos esforços devido aos cabos protendidos em um conjunto de cargas equivalentes. Também é proposto um modelo de cálculo para determinação da posição do cabo de protensão em elevação e das perdas imediatas da força de protensão (perdas por atrito e recuo das ancoragens). São analisadas as tensões de serviço, para verificação da deformação, e as tensões últimas a que a laje protendida pode estar submetida, para o dimensionamento das armaduras ativa e passiva. / There is a recent trend, in Civil Engineering, toward automatized projects, aiming at the development of personal solutions, avoiding undesirable design repetitions. As an example, pre-tensioned plane plates give great layout flexibility, faster structural execution and reduction of the number and cross section of pillars, resulting in gains in the net area of the construction. One of the most common structures used as pre-tensioned plates is the flat slab, with or without enlargements near the pillars. The flat slab have advantages related to others (ribbed and others) mainly regarding its easier execution. These work presents a numerical model to calculate pre-tensioned flat slab by the Finite Element Method. The finite element used, isoparametric with 8 nodes, has 5 degrees of freedom per node: 3 degree of freedom regarding the Reissner-Mindlin´s plate bending theory and the 2 remaining regarding the plane stress state. The pre-tension is considered through the Load Equilibrium Method (created by T. Y. Lin and used AALAMI (1990)). The method consists in the transformation of loads due to pre-tensioned cables in one assemble of equivalent loads. Also, it is proposed a calculus model to determine the pre-tensioned cable elevation and the instantaneous losses of the pre-tensioned forces (losses by friction and partial retreat of the anchorage). The stress and deformation in service are analyzed as well as the ultimate stresses of the pre-tensioned plate can be subjected are verified, in order to design active and passive reinforcements.

abstract: The focus of this investigation includes three aspects. First, the development of nonlinear reduced order modeling techniques for the prediction of the response of complex structures exhibiting "large" deformations, i.e. a geometrically nonlinear behavior, and modeled within a commercial finite element code. The present investigation builds on a general methodology, successfully validated in recent years on simpler panel structures, by developing a novel identification strategy of the reduced order model parameters, that enables the consideration of the large number of modes needed for complex structures, and by extending an automatic strategy for the selection of the basis functions used to represent accurately the displacement field. These novel developments are successfully validated on the nonlinear static and dynamic responses of a 9-bay panel structure modeled within Nastran. In addition, a multi-scale approach based on Component Mode Synthesis methods is explored. Second, an assessment of the predictive capabilities of nonlinear reduced order models for the prediction of the large displacement and stress fields of panels that have a geometric discontinuity; a flat panel with a notch was used for this assessment. It is demonstrated that the reduced order models of both virgin and notched panels provide a close match of the displacement field obtained from full finite element analyses of the notched panel for moderately large static and dynamic responses. In regards to stresses, it is found that the notched panel reduced order model leads to a close prediction of the stress distribution obtained on the notched panel as computed by the finite element model. Two enrichment techniques, based on superposition of the notch effects on the virgin panel stress field, are proposed to permit a close prediction of the stress distribution of the notched panel from the reduced order model of the virgin one. A very good prediction of the full finite element results is achieved with both enrichments for static and dynamic responses. Finally, computational challenges associated with the solution of the reduced order model equations are discussed. Two alternatives to reduce the computational time for the solution of these problems are explored. / Dissertation/Thesis / Ph.D. Aerospace Engineering 2012

abstract: Tall buildings are spreading across the globe at an ever-increasing rate (www.ctbuh.org). The global number of buildings 200m or more in height has risen from 286 to 602 in the last decade alone. The increasing complexity of building architecture poses unique challenges in the structural design of modern tall buildings. Hence, innovative structural systems need to be evaluated to create an economical design that satisfies multiple design criteria. Design using traditional trial-and-error approach can be extremely time-consuming and the resultant design uneconomical. Thus, there is a need for an efficient numerical optimization tool that can explore and generate several design alternatives in the preliminary design phase which can lead to a more desirable final design. In this study, we present the details of a tool that can be very useful in preliminary design optimization - finite element modeling, design optimization, translating design code requirements into components of the FE and design optimization models, and pre-and post-processing to verify the veracity of the model. Emphasis is placed on development and deployment of various FE models (static, modal and dynamic analyses; linear, beam and plate/shell finite elements), design optimization problem formulation (sizing, shape, topology and material selection optimization) and numerical optimization tools (gradient-based and evolutionary optimization methods) [Rajan, 2001]. The design optimization results of full scale three dimensional buildings subject to multiple design criteria including stress, serviceability and dynamic response are discussed. / Dissertation/Thesis / M.S. Civil Engineering 2014

L‘amorçage et la propagation de microfissures dans les matériaux à haute résistance représente une part importante de la durée de vie en fatigue, en particulier dans le cas d‘un chargement à faible amplitude. Ces phénomènes, d‘un grand intérêt scientifique, ont été de plus en plus étudiés au cours des dernières années. L‘orientation cristallographique et les hétérogénéités de déformation induites influent sur l‘amorçage et le comportement des microfissures de fatigue tant que leur taille caractéristique est inférieure ou de l‘ordre de grandeur de la taille de grains. L‘objectif principal de cette étude est de caractériser l‘influence de la microstructure et d‘un chargement cyclique à amplitude variable sur la plasticité cristalline et plus précisément sur l‘amorçage de microfissures dans un acier inoxydable 304L. Le première partie de cette étude consiste à l‘amélioration de la loi de comportement cristalline Cristal ECP codée dans le logiciel éléments finis ABAQUS afin de mieux prendre en compte la distribution et l‘évolution de la densité de dislocations sur les systèmes de glissement. Ce travail permet également de décrire la formation des bandes persistantes de glissement qui sont responsables du durcissement et de l‘adoucissement cyclique. La seconde partie de cette étude concerne l‘évaluation de l‘influence de la microstructure sur les valeurs locales des paramètres mécaniques utilisés pour les critères de fatigue aussi bien macroscopiques que microscopiques, et relier ces valeurs à l‘amorçage de microfissures à l‘échelle cristalline. Pour ceci, une comparaison est réalisée entre les résultats expérimentaux d‘observation de surfaces et les simulations numériques d‘agrégats 3D présentant les orientations cristallines réelles de ces éprouvettes. La simulation de la plasticité cristalline peut apporter une contribution utile pour la prédiction de la localisation et de l‘intensité de l‘amorçage de microfissures de fatigue, mais également aider à choisir un critère d‘amorçage de microfissures basé sur des considérations mécaniques. La dernière partie de ce manuscrit porte sur les effets d‘un chargement d‘amplitude variable (séquence de surcharge) sur la plasticité cristalline et l‘amorçage de microfissures. Deux modes de chargement ont été considérés pour les essais de fatigue : contrainte contrôlée et déformation contrôlée. Les essais avec surcharge en contrainte contrôlée présentent une durée de vie plus importante (six à neuf fois) que les essais avec surcharge en déformation contrôlée, ce qui est lié au durcissement cyclique important du 304L. De plus, les simulations montrent que sous chargement à déformation contrôlée, l‘effet mémoire de la surcharge est dépendant du niveau du chargement qui suit la surcharge : cet effet mémoire est plus important dans le cas d‘un chargement à faible amplitude (fatigue à grand nombre de cycles) qu‘en fatigue oligocyclique à forte amplitude / Because fatigue crack initiation and propagation of microstructurally short cracks represent most of the fatigue life in high-strength materials, especially under low amplitude loading, the study of crack initiation is of significant importance and attracted increasing attention recently. As long as the microcrack size is comparable with the grain size, the microcrack initiation is strongly influenced by the crystallographic microstructure. The main purpose of this work is to study the influence of the microstructure and variable amplitude loading on cyclic plasticity and microcrack initiation in stainless steel 304L. The first part of this work aims at enriching the crystal plasticity code Cristal ECP to better simulate the evolution of dislocation densities on slip systems and formation of PSBs which are responsible for the fatigue cyclic hardening/softening behavior. The second part concerns the evaluation of the influence of local values of mechanical factors, issued from both macroscopic and microscopic fatigue criteria, on crack initiation in the grains through the comparison between experimental surface observations and numerical simulations of 3D aggregates with realistic crystallographic orientations. It is shown that the crystal plasticity simulation can give useful contributions to predict the crack initiation sites and severity, and help to select fatigue crack initiation criterion based on mechanical parameters which actually control the crack initiation. The last part studies the effects of the variable amplitude loading (high-low sequence) on cyclic plasticity and crack initiation. Both load- and strain-controlled fatigue tests were considered. Load-controlled tests present much longer lives (6 to 9 times) than in strain-controlled tests due to strain hardening. Furthermore, simulations show that under strain-controlled loading, memory effect of overload is dependent on the amplitude level of the low amplitude block, which is more significant in high cycle fatigue than in low cycle fatigue.

La evaluación de la capacidad de carga de pilotes juega un rol esencial en su diseño. Esta capacidad puede ser estimada por metodologías teóricas, soluciones analíticas o numéricas, o por métodos semi-empíricos, cuyas aplicaciones están generalmente basadas en resultados de ensayos en campo. Las formulaciones semi-empíricas son comúnmente las más usadas por ingenieros geotécnicos debido a que los métodos teóricos generalmente están limitadas a aplicaciones particulares. Esta investigación compara la capacidad de carga de pilotes excavados por medio de diferentes metodologías, basándose en pruebas de carga experimentales llevadas a cabo en los campos experimentales de la universidad de Brasilia y Campinas, en Brasil. Los métodos semi-empíricos determinan la capacidad de carga ya sea a través del control del asentamiento o extrapolación de la curva carga x asentamiento mientras que los métodos teóricos están basados tanto en soluciones analíticas como numéricas, siendo la última mencionada calculada a través del análisis de los elementos finitos. Las comparaciones que se dieron de las capacidades de carga medidas en pruebas de carga con las obtenidas en resultados numéricos y del control de asentamiento mostraron buenos resultados, mientras que se encontraron valores con mayores errores relativos de los esperados al compararse con las metodologías semi-empíricas. El caso del método teórico presentó conservativos resultados siempre y cuando se considerase el efecto de la fricción negativa. The evaluation of axial bearing capacity of piles plays an essential role in their design. It can be estimated by theoretical methods, through an analytical or numerical solution, or by semi-empirical methods, whose application is generally based on field test results. Semi-empirical formulations are often preferred by geotechnical engineers since theoretical approaches are generally limited to particular applications. This paper compares the axial bearing capacity of bored piles estimated by different methodologies, based on instrumented load tests carried out in both the Campinas and Brasilia university campus, in Brazil. The semi-empirical approach involved settlement control and extrapolation of load-settlement curve while the theoretical approach was based on both analytical and numerical solutions, the latter computed through finite element analyses. When compared to the ultimate load bearing capacity measured in the instrumented load tests, both numerical and the settlement control results showed close agreement, while the semi-empirical methods estimated major expected relative errors and the theoretical method presented conservative values when considering the negative skin friction effects.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A avaliaÃÃo estrutural de turbinas eÃlicas à um problema que depende de diversas variÃveis tais como o regime de ventos, tipo e dimensÃes da turbina eÃlica, bem como das incertezas relacionadas a esses fatores. Para inserir essas incertezas, sÃo estabelecidas distribuiÃÃes de probabilidade para os parÃmetros fÃsicos do meio. No presente trabalho, propÃe-se uma anÃlise estrutural probabilÃstica utilizando o mÃtodo de elementos finitos para avaliaÃÃo das incertezas associadas à geraÃÃo de energia eÃlica. Avalia-se a resposta da estrutura a cargas aleatÃrias, para uma anÃlise de estabilidade do sistema. Com esse intuito foi desenvolvido um modelo de elementos finitos baseado na plataforma ANSYS R capaz de reproduzir com fidelidade o comportamento da torre eÃlica submetida à cargas produzidas pelo vento nas pÃs. AtravÃs de uma abordagem estatÃstica, foi determinada a soluÃÃo modal e a resposta dinÃmica com respeito a cargas de vento aleatÃrias. Utilizou-se o mÃtodo Monte Carlo como o mÃtodo de anÃlise probabilÃstica. Uma vez que o carregamento à considerado aleatÃrio o objetivo foi determinar a variaÃÃo dos parÃmetros de saÃda, dadas as incertezas iniciais, analisar as caracterÃsticas das propriedades dos materiais, tensÃes, deslocamentos, frequÃncias naturais e da resposta de frequÃncia da estrutura a aleatoriedade do vento. Analisou-se a influÃncia de cada incerteza sobre a resposta no domÃnio da frequÃncia. A partir dos resultados, pode-se concluir que a ferramenta numÃrica utilizada à capaz de representar de forma eficiente modelos de processos estocÃsticos em estruturas para a geraÃÃo de energia eÃlica e realizar a anÃlise de sensibilidade das variÃveis dinÃmicas envolvidas. / A structural evaluation of wind turbines is an issue that depends on many variables such as the wind regime, type and size of the wind turbine as well as the uncertainties related to these factors. To enter these uncertainties are established probability distributions for the physical parameters of the medium. In this paper, we propose a probabilistic structural analysis using the finite element method to evaluate the uncertainties associated with wind power generation. Assesses the response of the structure to random loads, for an analysis of system stability. With this purpose we developed a finite element model based on ANSYS R platform able to faithfully reproduce the behavior of the tower subjected to wind loads produced by wind in spades. A statistical approach, we determined the solution modal and dynamic response with respect to random wind loads. We used Monte Carlo method as the method of probabilistic analysis. Once charging is considered the random objective was to determine the variation of output parameters, given the initial uncertainties, analyze the characteristics of material properties, stresses, displacements, natural frequencies and frequency response of the structure to randomness of the wind. We analyzed the influence of each uncertainty about the response in the frequency domain. From the results, it can be concluded that the numerical tool used may represent efficiently models of stochastic processes in structures for wind power generation and perform sensitivity analysis of dynamic variables involved.

Adsorption is a retention mechanism of fluid molecules on solid surfaces and presents a wide range of applications, such as refrigeration, separation processes and fuel storage. This work describes the modelling of gas adsorption on porous media and presents an optimisation approach for the design of adsorption systems based on topology optimisation. A comprehensive formulation for the adsorption and desorption phenomena is presented, detailing the derivation of their weak forms and assembling the matrices for the implementation of the Finite Element Method (FEM). The sensitivities of objective functions to topology optimisation design variables are obtained by the adjoint method, which is presented in detail. The numerical implementation is aided by FEniCS and Dolfin Adjoint packages, resulting in a generic software for the optimisation of adsorption systems. The method is applied for the design of Adsorbed Natural Gas (ANG) tanks for on-demand consumption. Optimised tank layouts are proposed and compared with standard tanks, presenting improvement of the design objectives. / Adsorção é um mecanismo de retenção de moléculas de um fluido em superfícies sólidas e apresenta um vasto campo de aplicações, como em refrigeração, processos de separação e armazenamento de combustível. Este trabalho descreve o modelo de adsorção de gás em meios porosos e define uma abordagem de otimização de sistemas de adsorção baseada no Método de Otimização Topológica (MOT). Uma formulação abrangente para os fenômenos de adsorção e dessorção é apresentada, detalhando a dedução de seus formas fracas e montagem das matrizes para a implementação do Método dos Elementos Finitos (MEF). As sensibilidades das funções-objetivo em relação às variáveis de projeto são obtidas pelo método adjunto, que também é apresentado em detalhe. A implementação numérica é auxiliada pelos pacotes FEniCS e Dolfin Adjoint, originando uma ferramenta genérica para a otimização de sistemas de adsorção. Este método é aplicado ao projeto de tanques de Gás Natural Adsorvido (GNA) visando transporte, armazenamento e consumo. Tanques otimizados são propostos e comparados com tanques tradicionais, apresentando melhora dos objetivos de projeto.

O propósito principal do presente trabalho é estabelecer diretrizes para o uso de elementos finitos sólidos na modelagem de estruturas delgadas submetidas à flexão. Por meio de um conjunto de problemas estudou-se o travamento de elementos finitos da elasticidade bi e tridimensionais, quando usados para modelar estruturas delgadas submetidas à flexão. Foram usados elementos planos de 4, 8 e 9 nós e elementos tridimensionais de 4, 10, 11, 8, 20 e 27 nós, considerando elementos não distorcidos e distorcidos. A análise dos resultados nesses modelos permitiram entender melhor o comportamento e o uso de elementos sólidos em estruturas delgadas. / The main objective of the present work is to establish guidelines for the use of solid finite elements in the modeling of thin structures submitted to bending. By means of a set of problems the locking of elements three-dimensional and two-dimensional elasticity was studied, when used to model problems thin structures subjected to bending. We use 2-D displacements-based elements of 4, 8 and 9 nodes and 3-D displacement based of 4, 10, 11, 8, 20 and 27 nodes, considering undistorted and distorted elements. The analysis of the results of these models lead to the understanding of the behavior and the use of solid elements in thin structures.

As ferrovias, muito importantes para o transporte de pessoas e mercadorias, são também grandes fontes de ruído e vibração no meio urbano e rural. Os esforços dinâmicos devido ao contato aço-aço, entre as rodas e trilhos, são transmitidos à fundação da via e geram ondas vibratórias que se propagam pelo solo até atingir um receptor. Devido aos potenciais danos causados por essas excitações, modelos matemáticos capazes de prever e realizar a propagação das vibrações são de grande importância, podendo nortear ações mitigatórias. Neste contexto, este trabalho propõe a criação de um modelo numérico, utilizando-se de dinâmica multicorpos imerso em um ambiente de elementos finitos com não linearidade geométrica, que procure representar a interação dinâmica no sistema veículo-via e que permita analisar o comportamento das forças de contato roda-trilho. Tal modelo é utilizado com o objetivo de analisar e compreender como as forças dinâmicas de contato são influenciadas pelas características do veículo e da via. Alguns estudos sequenciais foram realizados. Iniciou-se com a avaliação do comportamento do veículo ao trafegar em uma superfície plana. Sequencialmente, considerou-se o veículo trafegando sobre modelos de vigas rígidas, representando os trilhos. Neste caso foram estudados cenários de rolamento e deslizamento. Posteriormente, o valor de uma rigidez equivalente da via foi avaliado por meio de um modelo estrutural e incorporado em um estudo para análise das forças de impacto das rodas ao passarem sobre descontinuidades em trilhos. Os resultados deste trabalho podem ser utilizados como dados de entrada para futuros modelos para previsão de propagação de ondas no solo devido às cargas ferroviárias. / Railways are important to freight and people transportation but are also one of the greatest sources of vibration in urban and rural environments. Dynamic loads are generated in steel-steel contact between wheels and rails and are transferred to foundation. They generate oscillatory waves that propagate through the ground, until finding a receptor. Potential damage due to ground borne vibration has increased the importance of predicting and calculating wave propagation with the aid of computational models, serving as guidelines for mitigating actions. On this context, the present work proposes a numerical model, adopting a multibody rigid-flexible dynamics formulation, based on a nonlinear geometrically-exact finite element description. The aim is to represent the dynamic interaction between the vehicle and the railway, permitting one to analyze wheel-rail contact forces. The model represents the dynamic interaction between vehicle and track and allows one to analyze how the dynamic contact forces are influenced by vehicle and railway characteristics. Some sequential studies were performed, starting from the evaluation of a vehicle running on a plane surface. Next, the scenario of a vehicle running on rigid beams representing the rails was simulated. In this case both sliding and sticking scenarios of contact were considered. Then, the value of an equivalent track stiffness was obtained by a structural model. It was taken as input to another study, which analyzed impact forces between wheels and rails when the vehicle experiences the passage by a discontinuity on the track. The results of the present work may be useful as input data for future prediction models of ground borne vibration due to railway dynamic forces.

Os métodos de equilíbrio limite comumente utilizados no dimensionamento de estruturas de solo grampeado não oferecem informação sobre as tensões e deformações na estrutura. No entanto, o êxito da técnica pressupõe deslocamentos para que a resistência dos grampos seja mobilizada. Portanto, seria desejável conhecer: os deslocamentos que a estrutura. sofre durante e depois de realizado o processo da escavação; os esforços mobilizados nos grampos; e a distribuição de tensões atrás da parede da escavação. A importância deste estudo é maior em situações em que a previsão do comportamento é a responsável por garantir a segurança de construções e de instalações de serviço público próximas às escavações grampeadas. Análises bidimensionais e tridimensionais de tensão-deformação com elementos finitos foram realizadas para um melhor entendimento do comportamento da estrutura. As comparações dos resultados das modelagens numéricas permitiram conhecer várias vantagens e desvantagens de um e de outro tipo de modelagem. Realizaram-se também comparações entre resultados de modelagens numéricas que utilizaram os seguintes modelos constitutivos: elasto-plástico (com critério de ruptura de Mohr-Coulomb), hiperbólico e elástico-linear, sendo que para este último realizou-se uma análise incremental. Para a aplicação do modelo elástico-linear foi necessária a divisão do maciço em regiões em função do tipo de trajetória de tensão. Essas comparações permitiram concluir que, desde que com a correta especificação dos parâmetros elásticos, a modelagem baseada na Teoria da Elasticidade pode representar bem o comportamento de escavações grampeadas. / The limit equilibrium methods that are frequently used for design of soi nailing structures do not provide information about the structure\'s stress and strain. However, the technique\'s success depends on the displacements that mobilize the nails strength. Therefore it is desirable to predict the structure\'s displacement, during and after the excavation; the forces avting on nails; and the stress distribution behind the excavation wall. This study has its importance increased in situations in which the prediction of the behavior is needed to guarantee the safety of adjacent buildings and municipal installations near to the excavation. Three dimensional and two-dimensional fine element stress-strain analyses were carried out for a better understanding of the behavior of the structure. Comparisons of the results of different numerical models led to a clear picture of advantages and disadvantages of different approaches. Numerical comparisons were also carried out between analyses with different constitutive models: elasto-plastic (Mohr-Coulomb), hyperbolic and incremental linear elastic. Application of the linear elastic model required the division of the soil mass in regions, according to stress path. Those comparisons led to the conclusion that, given correctly specified elastic parameters, Theory of Elasticity is able to correctly model the behavior of nailed excavations.