[pt] Funções Wavelet de suporte compacto têm sido recentemente aplicadas na resolução numérica de equações diferenciais com resultados bastante promissores. A partir do sucesso do uso das wavelets de Daubechies em diversos métodos como o de Galerkin, surgiram novas famílias de wavelets para a resolução de problemas específicos. Nesse contexto, vale destacar uma família de wavelets com características de funções interpoladoras chamadas Interpolets. Este trabalho tem como uma de suas contribuições a formulação de elementos finitos baseados em funções wavelet de Daubechies e interpolets de Deslauriers-Dubuc para sua utilização em problemas dinâmicos como a propagação de ondas em estruturas, além de problemas não-lineares como o cálculo de cargas críticas de flambagem para colunas e pórticos. A partir dessa formulação, o Método de Wavelet-Galerkin foi adaptado para a solução direta das equações diferenciais através de uma implementação que não depende da discretização do sistema em graus de liberdade (formulação sem-malha ou meshless). Este tipo de abordagem permite também explorar ao máximo as propriedades de multirresolução das wavelets. Diversos exemplos com descontinuidades e não-linearidades foram estudados com êxito. / [en] The use of compactly supported wavelet functions has become increasingly popular in the development of numerical solutions for differential equations. Daubechies wavelets have been successfully used as base functions in several schemes like the Galerkin Method. Meanwhile, Deslauriers and Dubuc developed a new wavelet family with interpolating characteristics called Interpolets. One important contribution presented in this work is the formulation of Finite Elements based in Daubechies wavelets and Deslauriers-Dubuc interpolets. Dynamic problems like wave propagation and structural stability problems were used as examples for the validation of the Finite Elements. The Wavelet-Galerkin Method has then been adapted for the direct solution of differential equations in a meshless formulation. This approach enables the use of a multiresolution analysis. Several examples with discontinuities and nonlinearities were studied successfully.

[pt] Nesta dissertação estuda-se a flambagem e o comportamento pós-crítico inicial de pórticos planos através da formulação de elementos finitos com graus de liberdade adicionais para posterior implementação no programa de análise FTOOL. Realizaram-se análises linearizadas para a determinação das cargas críticas clássicas e modos de flambagem de colunas com diferentes condições de contorno. Em um segundo momento, realizaram-se testes numéricos no sentido de prever a estabilidade do caminho pós-crítico (sensibilidade a imperfeições) de algumas estruturas cujos resultados analíticos são conhecidos. Finalmente, criaram- se alguns exemplos no FTOOL para comprovar a sua eficácia na obtenção de cargas críticas e avaliação do comportamento pós-crítico inicial de pórticos planos. Utilizou-se o pórtico de Roorda como exemplo para a detecção da sensibilidade a imperfeições, devido à sua simplicidade e ao conhecimento dos seus resultados analíticos. / [en] The buckling and post-buckling behavior of portal frames are studied by the formulation of finite elements with additional degrees of freedom in order to implement a new routine for obtaining critical loads in FTOOL, a structural analysis educational interactive system. Linearized analyses were performed in order to obtain critical loads and buckling modes for columns with different boundary conditions. Later, numerical tests were done in order to predict the stability of the post- critical path (sensitivity to imperfections) of some structures which analytical results are known. Finally, some examples were modeled in FTOOL to verify its accuracy in obtaining critical loads of portal frames. Roorda s frame was used as an example for the detection of the sensitivity to imperfections, based on its simplicity and knowledge of its analytical results.

Made available in DSpace on 2014-12-17T14:57:54Z (GMT). No. of bitstreams: 1 RenataCTSF_TESE_1-81.pdf: 4666386 bytes, checksum: 75d1cdda6a2cab121f77f0774f7de4e7 (MD5) Previous issue date: 2012-09-14 / There are a number of damaging mechanisms that various materials can suffer in service. However, when working with polymer composite materials, this is something that requires analysis, especially when exposed to adverse environmental conditions. Thus, the objective of the present thesis is the study of the direct influence of environmental aging and the form of hybridization of the reinforcement woven on the structural stability, surfacedegradation and fracture process of polymer composites laminates. For this, the development of two polymer composite laminates was necessary, where one of them was reinforced with a bi-directional woven with hybrid strandsofkevlar-49/glass-Efibers, and the other also with a bi-directionalwoven, however with weft and warpformed of alternating strandsof Kevlar-49 fibers and glass-E fiber The reinforcementwoven are industrially manufactured. Both laminates use a polyester resin as a matrixand are made up of four layers each. All laminates were industrially prepared by the hand lay-up method of manufacturing. To do this, test specimens were manufactured of the respective laminates and submitted to environmental aging accelerated through the aging chamber. They were exposed to alternating cycles of UV radiation and moisture (heated steam) for a standard defined period. At the end of the exposure period the specimens were subjected to mechanical tests of uniaxial tensile and bending in three points and to the characterizationsof the fracture and surface deterioration. In addition, they were submitted to a structural degradation assessment by the measurement of mass variation technique (MMVT) and the measurement of thickness variation technique (MTVT), this last technique being developed in this thesis. At the end of the analysis it was observed that the form of hybridization of the reinforcement woven and the aging process directly influence with losses or gain in mechanical properties, with losses in the structural degradation and in the formation and propagation of damage mechanism of the developedcomposite laminates / S?o v?rios os mecanismos de danos que os diversos materiais podem sofrer em servi?o. No entanto, ao se trabalhar com os materiais comp?sitos polim?ricos isso ? algo que necessita de an?lises principalmente quando expostos a condi??es ambientais adversas. Logo, a respectiva tese objetiva o estudo da influ?ncia direta do envelhecimento ambiental e da forma de hibridiza??o dos tecidos de refor?o no comportamento mec?nico, degrada??o estrutural (dimensional e de massa) de laminados comp?sitos polim?ricos. Para tanto se fez necess?rio o desenvolvimento de dois laminados comp?sitos polim?ricos, onde um deles ? refor?ado com um tecido bidirecional com mecha h?brida de fibras de kevlar-49/vidro-E e o outro com um tecido tamb?m bidirecional, por?m com trama e urdume formadas com mechas alternadas de fibras kevlar-49 e fibras de vidro-E. Os tecidos de refor?o s?o de fabrica??o industrial. Ambos os laminados utilizam como matriz a resina de poli?ster, sendo constitu?dos de quatro camadas cada. Todos os laminados foram confeccionados industrialmente pelo m?todo de fabrica??o handlay-up. Desta forma, foram fabricados corpos de provas (CP s) dos respectivos laminados e submetidos ao envelhecimento ambiental acelerado atrav?s da c?mara de envelhecimento. Os mesmos foram expostos aos ciclos alternados de radia??o UV e umidade (vapor aquecido) por um per?odo definido em norma. Ao t?rmino do per?odo de exposi??o os CP s foram submetidos aos ensaios mec?nicos de tra??o uniaxial e flex?o em tr?s pontos e ?s caracteriza??es da fratura e da deteriora??o superficial. Al?m disso, foram submetidos ? avalia??o da degrada??o estrutural mediante a t?cnica de media??o de varia??o de massa (TMVM) e a t?cnica de medi??o de varia??o de espessura (TMVE), sendo essa ?ltima desenvolvida nesta tese. Ao t?rmino das an?lises foi observado que a forma de hibridiza??o dos tecidos de refor?o e o processo de envelhecimento influenciam diretamente, seja com perdas ou ganho naspropriedades mec?nicas, com perdas na degrada??o estrutural e na forma??o e propaga??o do mecanismo de dano dos laminados comp?sitos desenvolvidos

Made available in DSpace on 2014-12-17T14:57:54Z (GMT). No. of bitstreams: 1 RaimundoNBF_TESE_1-104.pdf: 5288172 bytes, checksum: 0543c551bb4ef0aded2a4c286f66043d (MD5) Previous issue date: 2012-09-28 / The application of composite materials and in particular the fiber-reinforced plastics (FRP) has gradually conquered space from the so called conventional materials. However, challenges have arisen when their application occurs in equipment and mechanical structures which will be exposed to harsh environmental conditions, especially when there is the influence of environmental degradation due to temperature, UV radiation and moisture in the mechanical performance of these structures, causing irreversible structural damage such as loss of dimensional stability, interfacial degradation, loss of mass, loss of structural properties and changes in the damage mechanism. In this context, the objective of this thesis is the development of a process for monitoring and modeling structural degradation, and the study of the physical and mechanical properties in FRP when in the presence of adverse environmental conditions (ageing). The mechanism of ageing is characterized by controlled environmental conditions of heated steam and ultraviolet radiation. For the research, it was necessary to develop three polymer composites. The first was a lamina of polyester resin reinforced with a short glass-E fiber mat (representing the layer exposed to ageing), and the other two were laminates, both of seven layers of reinforcement, one being made up only of short fibers of glass-E, and the other a hybrid type reinforced with fibers of glass-E/ fibers of curaua. It should be noted that the two laminates have the lamina of short glass-E fibers as a layer of the ageing process incidence. The specimens were removed from the composites mentioned and submitted to environmental ageing accelerated by an ageing chamber. To study the monitoring and modeling of degradation, the ageing cycles to which the lamina was exposed were: alternating cycles of UV radiation and heated steam, a cycle only of UV radiation and a cycle only of heated steam, for a period defined by norm. The laminates have already undergone only the alternating cycle of UV and heated steam. At the end of the exposure period the specimens were subjected to a structural stability assessment by means of the developed measurement of thickness variation technique (MTVT) and the measurement of mass variation technique (MMVT). Then they were subjected to the mechanical tests of uniaxial tension for the lamina and all the laminates, besides the bending test on three points for the laminates. This study was followed by characterization of the fracture and the surface degradation. Finally, a model was developed for the composites called Ageing Zone Diagram (AZD) for monitoring and predicting the tensile strength after the ageing processes. From the results it was observed that the process of degradation occurs Abstract Raimundo Nonato Barbosa Felipe xiv differently for each composite studied, although all were affected in certain way and that the most aggressive ageing process was that of UV radiation, and that the hybrid laminated fibers of glass-E/curaua composite was most affected in its mechanical properties / A aplica??o dos materiais comp?sitos e em particular os pl?sticos refor?ados por fibras (PRF) tem conquistado espa?o, gradativamente, dos materiais ditos convencionais, por?m desafios t?m sido colocados quando sua aplica??o ocorre em equipamentos e estruturas mec?nicas que ficar?o expostos a condi??es ambientais adversas, principalmente quando se tem a influ?ncia da degrada??o ambiental do tipo temperatura, radia??o UV e umidade, no desempenho mec?nico dessas estruturas, ocasionando danos estruturais irrevers?veis tais como: perda de estabilidade dimensional, degrada??o interfacial, perda de massa, perda das propriedades estruturais e altera??es no mecanismo de dano. Neste contexto a presente tese tem como objetivo o desenvolvimento de um processo de monitoramento e modelagem da degrada??o estrutural, e o estudo das propriedades f?sicas e mec?nicas, em PRF quando em presen?a de condi??es ambientais adversas (envelhecimento). O mecanismo de envelhecimento ? caracterizado por condi??es ambientais controladas de vapor aquecido e de radia??o ultravioleta. Para a pesquisa foi desenvolvido tr?s comp?sitos polim?ricos, o primeiro uma l?mina de resina poli?ster refor?ado com manta de fibras curtas de vidro-E (representando a camada exposta ao envelhecimento) e dois laminados, ambos de sete camadas de refor?o, sendo um constitu?do s? com manta de fibras curtas de vidro-E, e o outro do tipo h?brido refor?ado com fibras de vidro-E/fibras de curau?. Ressalta-se que os dois laminados t?m a l?mina de fibras curtas de vidro-E como camada de incid?ncia do processo de envelhecimento. Os corpos de provas (CP s) foram retirados dos comp?sitos citados e submetidos ao envelhecimento ambiental acelerado atrav?s da c?mara de envelhecimento. Para o estudo do monitoramento e modelagem da degrada??o, os ciclos de envelhecimento a que foram expostos ? l?mina foram: ciclos alternados de radia??o UV e vapor aquecido, ciclo somente de radia??o UV e o ciclo somente de vapor aquecido, por um per?odo definido em norma. J? os laminados foram submetidos a apenas ao ciclo alternado de UV e vapor aquecido. Ao t?rmino do per?odo de exposi??o os CP s foram submetidos ? avalia??o da estabilidade estrutural mediante a t?cnica desenvolvida de medi??o de varia??o de espessura (TMVE) e a t?cnica de media??o de varia??o de massa (TMVM). Em seguida os mesmos foram submetidos aos ensaios mec?nicos de tra??o uniaxial para a l?mina e todos os laminados, al?m do ensaio de flex?o em tr?s pontos para os laminados. Esse estudo foi seguido da caracteriza??o da fratura e da degrada??o superficial. Por fim, foi desenvolvido um modelo para os Resumo Raimundo Nonato Barbosa Felipe xii comp?sitos denominado de Diagrama da Zona de Envelhecimento (DZE) para o monitoramento e predi??o da resist?ncia mec?nica ? tra??o ap?s os processos de envelhecimento. Ao t?rmino das an?lises foi observado que o processo de degrada??o se d? de forma diferente para cada comp?sito pesquisado, no entanto todos foram afetados, o processo de envelhecimento mais agressivo foi o de radia??o UV, e que o comp?sito que foi mais afetado em suas propriedades mec?nicas foi o laminado h?brido de fibras de vidro-E/curau?

Barras compostas em dupla cantoneira são constituídas por duas seções idênticas dispostas paralelamente, afastadas entre si e ligadas uma a outra apenas em alguns pontos ao longo do comprimento, por meio de chapas separadoras. O sistema aqui apresentado é bastante utilizado, principalmente em estruturas treliçadas leves, no entanto, não existem estudos específicos sobre seu comportamento, como conseqüência as normas de cálculo não fornecem subsídios para o projeto desse componente estrutural. É relevante estudar o comportamento de barras em dupla cantoneira, já que neste caso, além dos modos de instabilidade associados à cantoneira isolada, poderão ocorrer modos de instabilidade associados à barra composta em função da presença das chapas separadoras, que tendem a modificar o comportamento do sistema. Apresenta-se no trabalho análises numérica e experimental sobre o comportamento de barras submetidas à compressão centrada e excêntrica. Nas análises variou-se o número de chapas separadoras buscando estudar a eficiência das mesmas na força normal resistente das barras. Os resultados mostraram que a introdução de chapas separadoras melhorou significativamente o comportamento das barras, principalmente para compressão excêntrica. Foram observados modos de instabilidade por flexo-torção, por flexão e combinação dos dois modos. Para comparação dos resultados, inicialmente foram adotadas duas hipóteses de cálculo com base no procedimento da ABNT NBR 14762:2010, considerando compressão centrada. No primeiro procedimento considerou-se cada cantoneira como uma barra isolada independente da presença das chapas separadoras, admitiu-se instabilidades local, por flexo-torção e por flexão; no segundo considerou-se barra composta admitindo-se apenas instabilidades local e por flexão em relação ao eixo principal de menor inércia do conjunto. Em geral, os resultados das análises numérica e experimental apresentaram valores intermediários aos obtidos pelas duas hipóteses adotadas inicialmente. Com os resultados obtidos nas análises numérica e experimental são recomendados procedimentos para o dimensionamento desse componente estrutural. / Double-angle members with batten plates consist of two identical angles set up in parallel, spaced apart, and connected to each other by batten plates at specified points along the length. The system presented herein is widely used, especially in light truss structures; however, there are no standard design procedures specific for the design of this structural component. Studying the behavior of double angle members is interesting, because in this case, besides the critical modes of the single angle, they also show critical modes, due to the presence of the batten plates that sometimes interfere with the behavior of the system. This work presents a numerical and experimental study of members under concentric and eccentric axial compression. The number of batten plates is changed to study the influence on the nominal axial strength. The use of batten plates significantly increases the strength of the system, especially for members under eccentric compression. The buckling modes observed were flexural-torsional, flexural and combination of the modes. Initially, two design hypotheses are compared to the results obtained: (i) non-composite action (no interaction between angles), with only local, flexural, and flexural-torsional buckling considered; (ii) composite action (full interaction between angles), and only considering local and minor-axis flexural buckling of the pair of angles. The two design hypotheses ignore load eccentricity. The hypotheses are based upon recommendations in ABNT NBR 14762:2010. In general, numerical and experimental results for angles connected by bolted batten plates fall in between the design curves defined by methods (i) and (ii). With the results obtained in numerical and experimental analysis, procedures are recommended for the design of this structural component.

Esse trabalho apresenta um estudo comparativo entre métodos simplificados para avaliação da estabilidade de pórticos planos de aço. Aspectos relacionados à classificação das estruturas de aço quanto à deslocabilidade e sistema de contraventamento são apresentados e discutidos. O tradicional procedimento do comprimento efetivo de flambagem, ainda presente em algumas normas, é confrontado com métodos que empregam forças horizontais fictícias para contabilizar os efeitos desestabilizantes, tais como imperfeições geométricas iniciais e tensões residuais. Uma análise numérica avançada via MEF que permite a modelagem explícita dos efeitos que contribuem para a instabilidade de pórticos é empregada como referência na comparação dos resultados. É avaliada a resposta de pilares isolados, edifícios industriais e de múltiplos andares. Os métodos que empregam forças horizontais fictícias foram considerados adequados, pois além de eliminar o cálculo do comprimento efetivo de flambagem, apresentaram resultados mais consistentes em relação à análise avançada. / Two strategies for assessing steel frame stability and beam-column design are studied and compared. Some aspects related to bracing system and sway or non-sway classification are also discussed. The traditional procedure based on effective lengths are compared with some approaches based on notional loads, which propose a set of notional horizontal loads for account stability effects such as initial geometric imperfections and residual stresses. The results are compared with an advanced analysis using FEM, which consists in an explicit modeling of stability effects. Some industrial and multistory frames are studied and the results show that the notional load based procedures are accurate. These procedures are also practical because the need for effective length factors is eliminated.

Chassis is the primary structural component of an automobile. It is the main supporting structure of a vehicle to which all other systems like braking, suspension and differential are attached. In this thesis, a methodology for L7e category vehicle chassis design and structural stability analysis is presented. The present car being developed at Uniti Sweden AB is classified as L7e category vehicle as per the European Union, therefore the chassis developed in this thesis considers the specific characteristics that vehicles under this category demands for. A literature study is carried out to review various existing designs of vehicle chassis, latest innovations and advanced materials used to manufacture the same. The various types of forces and stresses commonly acting on chassis structures are analyzed and their effects on the vehicle is understood. After completing literature study, several findings are listed in a systematic manner, by providing ample arguments to justify each of them. The pro-con analysis is conducted to evaluate merits and demerits of each alternative type of chassis and the material to manufacture it. The most essential design criteria are derived from the QFD (Quality function deployment) which then acts as important guidelines during the actual design process. Structural chassis frame is designed as per the design criteria, using the CAD software CATIAV5R19 and the structural stability of the same is tested and analyzed using ANSYS 15.0 software. From the results of these analysis tests the static structural stability of the design is confirmed.

This thesis dealt with thermal stability of magnesium alloy AZ91 prepared by severe plastic deformation, which leeds to fine grained structure. This structure is characterised by its inherent instability and this thesis tries to find out the value of critical temperature and rate of this instability, which manifests as grain coarsening.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Standards define target reliability levels that govern the safety of designed structures. These target levels should be around an economic optimum for the class of structure under consideration. However, society may have safety requirements in excess of that required to achieve an economic optimum. The LQI criterion can be used to determine society’s willingness to invest in safety, thereby defining a minimum acceptable safety- or reliability level. This thesis determines economically optimised reliability levels for reliability class two concrete structures in South Africa, over a range of typical input parameters. Rackwitz’s (2000) approach is used here, adjusted for the South African context. The structure is described using a simple limit state function, defined as the difference between load and resistance, with resistance a function of a global safety parameter. South African construction costs, costs of increasing safety, failure costs and discount rates are used in the objective function for economic optimisation. Life Quality Index (LQI) theory is used as a basis to derive society’s willingness to pay (SWTP) for safety and the corresponding reliability level is found by applying the LQI criterion. In the South African context the derivation of SWTP presents some challenges, which is discussed. Situations where the minimum required reliability would exceed the economically optimum reliability level are discussed. Various reliability based cost optimization case studies are conducted covering a broad range of typical concrete design situations. From these case studies a range of target reliability indices are derived for typical concrete structural components and failure modes. Obtained values are compared to current South African target levels of reliability provided by the South African loading code and recommendations are made. The approach used by Rackwitz (2000) is compared with results obtained from case studies and used as basis to estimate optimum reliability levels for other types of buildings. Functions are written in MATLAB to allow replication of the study for others seeking to derive optimum reliability indices. / AFRIKAANSE OPSOMMING: Standaarde spesifiseer teiken betroubaarheidsvlakke wat die veiligheidsvlak van ontwerpte strukture bepaal. Hierdie teikenvlak moet rondom die ekonomiese optimum wees vir die klas van struktuur onder oorweging. Die samelewing verkies moontlik ‘n hoër veiligheidsvlak as wat deur die ekonomiese optimum dikteer word. Die LKI (Lewens Kwaliteit Indeks) maatstaf kan gebuik word om die samelewing se bereidwilligheid om in veiligheid te belê te bepaal en sodoende ‘n minimum veiligheidsvlak bepaal. Hierdie tesis bepaal die ekonomiese optimum betroubaarheidsvlak vir klas twee beton strukture in Suid-Afrika vir wisselende parameters. Rackwitz (2000) se benadering word in hierdie studie gebruik en is aangepas vir Suid-Afrikaanse omstandighede. Die struktuur word beskryf deur ‘n eenvoudige limiet staat funksie, gedefinieer as die verskil tussen die las en weerstand, met die weerstand as die funksie van ‘n globale veiligheidsparameter. Suid-Afrikaanse konstruksie koste, veiligheidsvermedering koste, falingskoste en diskonteer koerse word gebruik vir optimering. Die LKI teorie word gebruik om SBB (Samelewing Bereidheid om te Belê) vir veiligheid af te lei en die ooreenkomstige betroubaarheidsvlak word bepaal deur die LKI maatstaf toe te pas. In die afleiding hiervan vir Suid-Afrikaanse omstandighede is sekere uitdagings teegekom wat bespreek word. Situasies waar die minimum betroubaarheidsvlak hoer is as die ekonomiese optimum word bespreek. Verskillende betroubaarheids gebaseerde optimering gevalstudies word gedoen op tipiese beton struktuur elemente. Van hierdie gevalstudies is optimum betroubaarheidsindekse vir die tipiese beton elemente en galingsmodusie afgelei. Die betroubaarheidsindekse word vergelyk met huidige betroubaarheidsindekse soos wat voorgeskryf is in die Suid-Afrikaanse laskode (SANS10160-1(2011)). Rackwitz (2000) se benadering word vergelyk met die resultate van die gevallestudies en word gebruik as basis om optimum betroubaarheidsvlakke vir ander tipes geboue te voorspel. MATLAB funksies is geprogrameer om minimum en optimum betroubaarheidsindekse af te lei.

Western Palm Beach County, FL is characterized by thick deposits organic soils at shallow depths. Because of their high void ratio and compressibility, these soils undergo large primary consolidation followed by extended periods of secondary compression causing excessive premature structural distress. Although soil stabilization has been largely used with remarkable results in soft, expansive and non-organic soils, limited research and practice exist in the implementation with highly organic soils. The main motivation of this research was to investigate the effects of cement stabilization on the compressibility behavior of organic rich soils, and develop mix design criteria for optimum cement contents necessary to induce the desired engineering behavior. This optimized mix design may provide guidelines for Deep Mixing Methods in organic soils. / by Juan Ramirez. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.