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Orientador: Gabriela Rezende Fernandes / Co-orientador: Rogério Oliveira Rodrigues / Banca: Renato Bertolino Junior / Banca: Carlos Humberto Martins / Resumo: No presente trabalho foi desenvolvida a formulação linear do método dos elementos de contorno para a análise estrutural de chapas com carregamento normais e tangenciais a sua superfície. A equação integral do deslocamento é deduzida a partir do Teorema de Reciprocidade de Betti, considerando espessura constante na chapa. Posteriormente foi detalhada a teoria para a análise não linear de chapas através do MEC (método dos elementos de contorno) introduzindo ao sistema de equações campos de esforços iniciais (ou plásticos) em células definidas no domínio. A solução não linear se obtém por uma formulação implícita, na qual as correções das deformações são feitas através do operador tangente consistente que se atualiza a cada nova iteração, levando a convergência quadrática do processo iterativo. Utilizou-se como critério de ruptura o de Von Misses. Exemplos foram analisados a fim de mostrar a convergência quadrática no processo iterativo e também a convergência dos resultados numéricos à medida que se refinava a discretização do contorno em elementos e do domínio em células / Abstract: In this paper the linear formulation of the boundary element method (BEM) for analyzing the stretching plate problem written in terms of displacements and tractions in the normal and tangential directions to the boundary has been developed. The integral equation of displacement is derived from Betti's reciprocity theorem, considering constant thickness on the plate. Then the BEM nonlinear formulation has been obtained by considering an initial (or inelastic) force field over the plate domain, requiring therefore the plate domain discretization into cells. The nonlinear solution is obtained by an implicit formulation, where the strains correction to be computed for each iteration is obtained by considering the consistent tangent operator, leading to a quadratic convergence rate in the iterative procedure required to achieve the plate equilibrium. In the numerical examples, the Von Mises criterion has been adopted to model the material behavior, showing the quadratic convergence rate. Besides different discratizations have been analyzed in order to show as well the results convergence / Mestre

Orientador: Eurípedes Guilherme de Oliveira Nóbrega / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-18T21:47:12Z (GMT). No. of bitstreams: 1 InocenteJunior_NilsonRoberto_M.pdf: 4529986 bytes, checksum: b2f87d6e91f48c6ad7f200beee40d1b7 (MD5) Previous issue date: 2011 / Resumo: O monitoramento da integridade de estruturas, também referido na literatura pelo termo Structural Health Monitoring (SHM), é um campo multidisciplinar de pesquisa que abrange técnicas, tecnologias e métodos que permitam um diagnóstico contínuo e inteligente da integridade de estruturas mecânicas. O desenvolvimento de estruturas mecânicas com maior durabilidade, maior segurança e menor custo de manutenção são as principais razões que justificam o investimento na pesquisa e desenvolvimento nessa área, por diversos setores da indústria e de serviços. Neste trabalho é estudada a aplicação de técnicas de identificação multivariável baseadas em subespaços, juntamente com geração e análise de resíduos de paridade como ferramentas para a realização da detecção de danos em estruturas mecânicas, o que representa a base de todo o procedimento de um diagnóstico estrutural completo. A realização deste trabalho envolveu a construção de uma bancada experimental para análise de danos em elementos de placa, com múltiplos sensores e atuadores. Como um dos passos principais deste trabalho também esteve o desenvolvimento de um método de identificação por subespaços com segmentação espectral, o que viabilizou uma melhoria na qualidade e redução no custo computacional da identificação da estrutura. Além disso, também foram estudadas técnicas de fusão dos dados de sinais dos sensores, visando melhoria na robustez da detecção. Os principais resultados obtidos neste trabalho servirão de base para o desenvolvimento de um sistema inteligente de diagnóstico estrutural em tempo real / Abstract: Structural Health Monitoring (SHM) is a multidisciplinary research field, which covers techniques, technologies and methods which are essential to perform a continuous and intelligent diagnosis about mechanical structure integrity. The development of structures with improved durability, improved operational safety and reduced maintenance cost are the main reasons that justify the investments in research and development in this area, by a numerous amount of industrial and services sectors. In this work, the application of multivariable identification subspace-based identification techniques with parity residue generation and analysis are studied as tools to perform structural damage detection, which is the basis of a complete structural diagnosis procedure. The realization of this work involved the construction of an experimental workbench to detect damages in plate elements, equipped with multiple sensors and actuators. The development of a subspace-based identification method with spectral segmentation that made possible to improve the quality and to reduce the computational cost of system identification was one of the major steps achieved in this work. Also, some data fusion techniques were studied, aiming to perform a more robust detection. The main results obtained in this work will be the basis to develop an intelligent and real-time structural diagnosis system / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

This thesis addresses the issues surrounding the application of the finite element method to analyse composite structure repairs with an emphasis on aircraft applications. A comprehensive literature survey has been carried out for this purpose and the results are presented. A preliminary study and a comparative study of different modelling approaches have been completed. These studies aim to explore and identify the problems in modelling repairso n simplec ompositep anelsw ith speciala ttention given to adhesivem odelling. Three modelling approaches have been considered: Siener's model which is an extension of the traditional plane strain 2D model used for adhesively bonded joints, Bait's model which is a promising new approach and a full 3D model. These studies have shown that these methods are complementary providing a different insight into bonded repairs. They have also highlighted the need for a new modelling approach which will provide an overall view of bonded repairs. Improved modelling approachesh ave been developedf or externallyb onded patch and flush repairs. These models enable the study of adhesive failure as well as composite adherendf ailures.T hesea pproachesh aveb eena ppliedt o real repairs and the predicted results compared to experimental data. Four case studies have been conducted: external bonded patch repairs to composite plates, a scarf joint for bonded repairs, a flat panel repaired with a scarfed patch and a repaired curved panel. These case studies have shown that bonded repairs to composite structures can be analyseds uccessfullyu sing PC-basedc ommercialf inite elementc odes.

This investigation was undertaken to develop plastic design aids to be used in the direct design of optimum frames. It uses the concept of minimum weight of plastically designed steel frames, and the concept of linear programming to obtain general solutions. Among the special characteristics of this study are: A. The integration of both gravity and combined loading conditions into one linear programming problem. B. The application of the revised simplex method to the dual of a parametric original problem. C. The application of A and B above in the development of design aids for the optimum design of symmetrical single-bay, single-story portal frame. Specifically, design graphs for different height to span ratios and different vertical load to lateral load ratios are developed. The use of these graphs does not require the knowledge of linear programming or computers on the part of the designer.

In order to overcome the difficulties encountered in closed form solutions, moment-curvature-thrust relationships are developed for hybrid and nonhybrid cross sections utilizing an open form method. The use of horizontal sectors permits the inclusion of residual stresses and/or nonbilinear stress-strain relationships, if desired. Theoretical and experimental data are compared. Applications to circular tubes and other cross sections are discussed. Results indicate that open form solutions are feasible for calculating moment-curvature-thrust data. Hybrid cross sections are easily treated by open form solutions.

The principle of sustainability in the built environment has become much more significant in the past decade, resulting in a push to develop building systems that are more energy efficient, durable, and use fewer natural resources. For residential and light commercial buildings, insulated concrete forms (ICF) have enjoyed increasing popularity for their ability to meet these new demands. ICFs are a stay-in-place concrete formwork system for building structural walls that are also highly insulated, among other benefits. Screen-grid ICFs (SGICF) are a small subset of ICFs that tend to use less concrete than standard ICFs and are sometimes made of recycled materials. These traits make SGICFs attractive, but there is a lack of understanding of their structural characteristics due to their irregular internal concrete structure. Because of this, structures using SGICFs are limited to heights no higher than two stories. Further study should show whether SGICFs structures can safely built to greater heights. This investigation studied two types of SGICFs at a component level in order to gain understanding of their lateral force and drift ratio capacities under cyclic loading. Several variables, including steel reinforcement details, the type of concrete, and the presence of the forms, were altered to measure their impact on the performance of the systems. Test results suggested that the ICF formwork increased lateral strength by up to 100% and lateral deformation capacity by up 60% when compared to identical specimens tested with the formwork removed. Results also showed that confinement of the cement, either by mesh hoops, spiral wire, or fiber-reinforced concrete improved the drift ratio at failure up to 500% when compared to specimens with no confinement material. Computer models were created to gauge their ability to replicate the behavior of the experimental test results. The models typically overestimated the lateral load resistance of the samples by 50-100%, and even more in some cases, depending on the reinforcement. The models were not reliable in determining the drift ratio at which the sample was considered to have failed. In some cases the model failed at 50% lower lateral deformations than the test specimen, while in others the model did not fail at all. Future studies should explore refinements of the models to increase their accuracy and usefulness, as well as accounting for the contributions do to the form material. Future studies should also include using spiral wires, mesh hoops, or fiber reinforced concrete in full-scale walls to verify their efficacy in improving overall wall performance.

The purpose of this thesis is to explore the civil engineering application of the law of virtual work to the determination of defelections, shears, bending stresses in truss structures, beams, structures subjected to both direct stress and bending, and indeterminate structures, and further to give examples of their mathematical solutions.

Scale model technology represents one method of investigating the behavior of advanced, weight-efficient composite structures under a variety of loading conditions. Testing of scale models can provide a cost effective alternative to destructive testing of expensive composite prototypes and can be used to verify predictions obtained from finite element analyses. It is necessary, however, to understand the limitations involved in testing scale model structures before the technique can be fully utilized. The objective of this research is to characterize these limitations, or scaling effects, in the large deflection response and failure of composite beams. Scale model beams were loaded with an eccentric axial compressive load designed to produce large bending deflections and global failure. / Ph. D.

A study was performed to develop an interactive plane frame analysis program. The program was designed to run on Unix-based workstations and to be independent of the hardware platform. This was achieved by selecting the XWindow system as the underlying graphical user-interface. An event-driven, window-based program was developed using the XWindow Toolkit. The entire program was written in the C programming language. The program consists of two parts: a preprocessor and a processor. The preprocessor employs pull-down menus and pop-up dialog boxes and provides a convenient way of creating and modifying structural models. The processor performs linear elastic analysis of plane frame structures based on the matrix displacement method. The processor computes joint displacements, support reactions and local member-end forces of the structure. It also handles internal hinges, joint loads, member loads, prescribed displacements, multiple load cases and load combinations. Other features include automatic mesh generation for orthogonal frames, automatic computation of self-weight and specification of output options. To verify the accuracy of the program, analysis results from the program were compared with results obtained from a commercial structural analysis program. A comparison of joint displacements, support reactions and member-end forces indicate that the difference in the values obtained from the two programs is less than two percent and that the program provides accurate analysis results. / Master of Science