A general procedure for the evaluation of the mechanical properties of structural joints, named component method, is now available from intensive research works at the European level. This procedure allows the analytical prediction of the resistance, but also of the stiffness and the deformation capacity, of structural joints under external forces (axial or shear forces, bending moments ). The component method is nowadays integrated as a reference procedure in two European design codes, respectively for steel structures (EC3 [EN1993]) and steel-concrete composite structures (EC4 [EN1994]). However, its potential scope is much larger and present studies are aimed to apply to situations as joints in fire, joints under seismic loading, joints under exceptional loads (Robustness Project) . More recently, a research project [CTI-2004] has succeeded in applying the component method to the investigation of the elastic behaviour of mechanical joints in timber construction. That is the result of the collaboration of CTIB-TCHN (Belgian Institute for Wood Technology) and University of Liège. The main principle of the component method is the following: identification of constitutive components subjected to tension, compression or shear in the joint; determination of the mechanical behaviour of these individual components; "assembling" components so as to derive the mechanical properties of the whole joint. In the present paper, timber joints with dowel fasteners are considered. Two components may be identified: "dowel" component (dowel fastener in bending and shear); embedding component (timber member in embedding). The "dowel" component is known from past researches, whereas little information is available for the embedding component. EC5 [EN1995] proposes formulation to predict the behaviour for joints composed of these two components; but it only depends on two factors: the dowel diameter and the timber density. The influence probably significant of the grain direction (material strongly anisotropy) and the thickness of the connected members are for instance neglected. Experimental, numerical and analytical investigations have recently been performed by University of Liège in collaboration with CTIB-TCHN so as to propose another formulation more precise for joints. Experimental results, performed by CTIB-TCHN, have been used as reference for the development of numerical model and, then, analytical model. The application of the component method to the prediction of the elastic behaviour of timber joints consist of two steps: "local" investigation on components that is to develop analytical models for the prediction of the elastic behaviour of components; "global" investigation on joints that is to develop analytical models for the prediction of the elastic behaviour of joints. The application of the component method to timber joints with dowel fasteners is a first step towards the use of this concept in future to others mechanical joints (screw, punched metal plate, nail, bolt ). In this case, others components may be derived to cover the field of application expected.

A rather complete picture of automatic plastic-hinge analysis onto steel frames under static loads is made in the present thesis. One/two/three-linear behaviours of mild steel are considered. The frames are submitted to fixed or repeated load. The geometric nonlinearity is taken into account. The beam-to-column joints of structures could be rigid or semi-rigid. The compact or slender cross-sections are examined. The investigation is carried out using direct or step-by-step methods. Both analysis and optimization methodologies are applied. From the fundamental theory to the computer program aspect are presented. Various benchmarks in open literatures are tested demonstrating the efficiency of the implementation.

For decades, structural engineers have been using various conventional design approaches for assessing the strength and stability of framed structures for various loads. Today, engineers are still designing without some critical information to insure that their stability assessment yields a safe design for the life of the structure with consideration for extreme loads. Presented in this thesis is new critical information provided from the study of stability analysis and design of steel framed structures accounting for extreme loads associated to load patterns that may be experienced during their lifetime. It is conducted in five main parts. A literature survey is first carried out reviewing the previous research of analyzing frame stability including the consideration of initial geometric imperfections, and also evaluating research of the analysis and design of the increased usage of cold-formed steel (CFS) storage racks. Secondly, the elastic buckling loads for single-storey unbraced steel frames subjected to variable loading is extended to multi-storey unbraced steel frames. The formulations and procedures are developed for the multi-storey unbraced steel frames subjected to variable loading using the storey-based buckling method. Numerical examples are presented as comparisons to the conventional proportional loading approach and to demonstrate the effect of connection rigidity on the maximum and minimum frame-buckling loads. Thirdly, the lateral stiffness of axially loaded columns in unbraced frames accounting for initial geometric imperfections is derived based on the storey-based buckling. A practical method of evaluating column effective length factor with explicit accounting for the initial geometric imperfections is developed and examined using numerical examples. The fourth part is an investigation of the stability for multi-storey unbraced steel frames under variable loading with accounting for initial geometric imperfections. Finally, the stability of CFS storage racks is studied. The effective length factor of CFS storage racks with accounting for the semi-rigid nature of the beam-to-column connections of such structures are evaluated based on experimental data. A parametric study on maximum and minimum frame-buckling loads with or without accounting for initial geometric imperfections is conducted. The proposed stability analysis of multi-storey unbraced frames subjected to variable loading takes into consideration the volatility of live loads during the life span of structures and frame buckling characteristics of the frames under any possible load pattern. From the proposed method, the maximum and minimum frame-buckling loads together with their associated load patterns provides critical information to clearly define the stability capacities of frames under extreme loads. This critical information in concern for the stability of structures is generally not available through a conventional proportional loading analysis. This study of work ends with an appropriate set of conclusions.

For decades, structural engineers have been using various conventional design approaches for assessing the strength and stability of framed structures for various loads. Today, engineers are still designing without some critical information to insure that their stability assessment yields a safe design for the life of the structure with consideration for extreme loads. Presented in this thesis is new critical information provided from the study of stability analysis and design of steel framed structures accounting for extreme loads associated to load patterns that may be experienced during their lifetime. It is conducted in five main parts. A literature survey is first carried out reviewing the previous research of analyzing frame stability including the consideration of initial geometric imperfections, and also evaluating research of the analysis and design of the increased usage of cold-formed steel (CFS) storage racks. Secondly, the elastic buckling loads for single-storey unbraced steel frames subjected to variable loading is extended to multi-storey unbraced steel frames. The formulations and procedures are developed for the multi-storey unbraced steel frames subjected to variable loading using the storey-based buckling method. Numerical examples are presented as comparisons to the conventional proportional loading approach and to demonstrate the effect of connection rigidity on the maximum and minimum frame-buckling loads. Thirdly, the lateral stiffness of axially loaded columns in unbraced frames accounting for initial geometric imperfections is derived based on the storey-based buckling. A practical method of evaluating column effective length factor with explicit accounting for the initial geometric imperfections is developed and examined using numerical examples. The fourth part is an investigation of the stability for multi-storey unbraced steel frames under variable loading with accounting for initial geometric imperfections. Finally, the stability of CFS storage racks is studied. The effective length factor of CFS storage racks with accounting for the semi-rigid nature of the beam-to-column connections of such structures are evaluated based on experimental data. A parametric study on maximum and minimum frame-buckling loads with or without accounting for initial geometric imperfections is conducted. The proposed stability analysis of multi-storey unbraced frames subjected to variable loading takes into consideration the volatility of live loads during the life span of structures and frame buckling characteristics of the frames under any possible load pattern. From the proposed method, the maximum and minimum frame-buckling loads together with their associated load patterns provides critical information to clearly define the stability capacities of frames under extreme loads. This critical information in concern for the stability of structures is generally not available through a conventional proportional loading analysis. This study of work ends with an appropriate set of conclusions.

In this study, weight optimization of two dimensional steel frames is carried out in which the flexibility of beam-to-column connections and the soil-structure interaction are considered. In the analysis and design of steel frames, beam-tocolumn connections are assumed to be either fully rigid or perfectly pinned. However, the real behavior of beam-to-column connections is actually between these extremes. Namely, even the simple connections used in practice possess some stiffness falling between these two cases mentioned above. Moreover, it is found that there exists a nonlinear relationship between the moment and beam-to-column rotation when a moment is applied to a flexible connection. These partially restrained connections influence the drift (P- effect) of whole structure as well as the moment distribution in beams and columns. Use of a direct nonlinear inelastic analysis is one way to account for all these effects in frame design. To be able to implement such analysis, beam-to-column connections should be assumed and modeled as semi-rigid connections. In the present study, beam-to-column connections are modeled as &ldquo / end plate without column stiffeners&rdquo / and &ldquo / top and seat angle with web angles&rdquo / . Soil-structure interaction is also included in the analysis. Frames are assumed to be resting on nonlinear soil, which is represented by a set of axial elements. Particle swarm optimization method is used to develop the optimum design algorithm. The Particle Swarm method is a numerical optimization technique that simulates the social behavior of birds, fishes and bugs. In nature fish school, birds flock and bugs swarm not only for reproduction but for other reasons such as finding food and escaping predators. Similar to birds seek to find food, the optimum design process seeks to find the optimum solution. In the particle swarm optimization each particle in the swarm represents a candidate solution of the optimum design problem. The design algorithm presented selects sections for the members of steel frame from the complete list of sections given in LRFD- AISC (Load and Resistance Factor Design, American Institute of Steel Construction). Besides, the design constraints are implemented from the specifications of the same code which covers serviceability and strength limitations. The optimum design algorithm developed is used to design number of rigid and semi-rigid steel frames.

[pt] O dimensionamento de estruturas de edifícios de aço com ligações do tipo semi-rígidas ainda enfrenta uma série de resistências por parte dos engenheiros estruturais. Este fato se deve em parte à falta de normas específicas, programas de computadores adequados e informações mais detalhadas sobre as vantagens econômicas das ligações semi- rígidas. Este trabalho apresenta um estudo paramétrico de uma edificação considerando o dimensionamento das ligações no regime semi-rígido. Estas investigações consideram parâmetros como: a rigidez das ligações, sistemas com estruturas em aço ou mistos e estabilidade lateral dos pórticos. A edificação analisada foi uma habitação popular padronizada de quatro pavimentos desenvolvida pela USIMINAS, muito difundida no Brasil. Em uma primeira etapa cada edifício foi estudado com uma rigidez de ligação semi- rígida padrão para todas as ligações da estrutura. Posteriormente ligações semi-rígida individualizadas foram adotadas para os diversos pórticos estudados. Este trabalho a princípio apresenta uma metodologia de análise e dimensionamento de estruturas em aço com ligações semi- rígidas com base no modelo de molas proposto pelo Anexo J Revisado do Eurocode 3. Com base nesta metodologia propõe- se um modelo simplificado de ligações semi-rígidas viga/coluna com o uso do programa ANSYS. Os modelos estruturais foram estudados com a inclusão dos efeitos da não linearidade geométrica dos pórticos e o comportamento elasto-plástico do material de forma a se obter resultados consistentes com os resultados experimentais e sem a introdução de coeficientes de correção. Os resultados obtidos neste trabalho foram apresentados, discutidos e comparados com os desenvolvidos pela USIMINAS de forma a se analisar o comportamento das ligações e sua eficiência. Para os edifícios considerados neste trabalho, onde se fez uso de ligações semi-rígidas padrão, o sistema mais econômico, com relação à peso de aço, foi a estrutura mista com contraventamentos (40 por cento da capacidade rígida) que teve uma economia de até 48 por cento em relação aos outros edifícios e de até 10 por cento aos sistemas da USIMINAS. Quando no uso de ligações otimizadas estas economias aumentam para 53 por cento e 15 por cento. Os resultados apresentados confirmam a vantagem da utilização deste tipo de ligação em edifícios residenciais em aço de pequena altura. / [en] Nowadays, despite the substantial increase in structural design knowledge, the semi-rigid connections steel design is still facing resistance from the structural engineers. This fact can be in part explained by few design standards that allows and explains their use, suitable computer programs and the lack of detailed information of the economical advantages of the semi-rigid design philosophy. This work presents a parametric analysis performed on a residential low-rise steel building considering all the steps necessary to a semi-rigid design. This analysis considered parameters like: beam-to-column connection stiffness and strength,structural system (steel or composite) and lateral frame stability (sway and non-sway frame solutions). The analysed structure consisted on a standard four pavements residential building proposed by a Brazilian Steel Mill Usiminas for low-cost popular constructions. Initially all the structure beam-to-column connections adopted a standard connection stiffness. The study continued with optimised connection stiffness for each of the designed structural frames. The first part of the present work is devoted to a full description of the design procedures proposed in the Eurocode 3, revised annex J for semi-rigid connection design. Based on this methodology a simple design model was proposed and implemented with the aid of the finite element program Ansys. The model included geometrical and material non- linearities and considered the connections semi-rigid behaviour avoiding the conventional approximations suggested in several current steel design standards. The results of this investigations are presented, discussed and compared to standard designs like the Usiminas proposal as means to access the economic potential and efficiency of the semi-rigid solutions. The best structural solution for the investigated construction was a non-sway composite semi- rigid (40 percent of the rigid capacity). The economy achieved were: 48 percent and 10 percent when compared to other semi-rigid solutions and the conventional Usiminas solution, respectively. This figures changed to 53 percent and 15 percent when optimised connections were used in each structural frame. The presented results confirm the advantage of the use of this connections kind in residential buildings in steel of low height.

[pt] Ao longo dos anos, a interação aço-concreto tem obtido um lugar de destaque do ponto de vista estrutural, ampliando a gama de soluções em concreto armado e aço, o que permite atender aos novos desafios arquitetônicos e às exigências que o mercado impõe. O objetivo do sistema misto é a combinação desses dois materiais, formando um único sistema estrutural em que a capacidade portante de cada elemento possa ser explorada ao máximo, tirando-se proveito da grande capacidade do concreto resistir a esforços de compressão, e de o aço, à tração. Essas características singulares de sistemas mistos aço-concreto conduzem a frequências naturais mais próximas da faixa de frequência de excitações associada às atividades humanas. Sendo assim, as considerações relacionadas ao projeto estrutural obrigam os engenheiros a fazer verificações quanto à resistência e à estabilidade de sistemas estruturais (estados limites últimos), mas os problemas relacionados ao estado limite de utilização desses sistemas devem ser analisados de forma mais cuidadosa. Embora o assunto de vibrações em lajes de edifícios induzidas por atividades humanas tem sido de continuado interesse a pesquisadores e a engenheiros ao longo dos últimos dois séculos (1828-2009), inexiste na literatura técnica, até onde o autor tem conhecimento, análise de correlações teórico-experimentais de vibrações de estruturas mistas aço-concreto sob ação de atividades humanas, na qual são consideradas a ortotropia, a interação parcial e as ligações semirrígidas. Com o objetivo de contribuir nessa direção, o presente trabalho investiga o efeito da interação aço-concreto sobre a resposta dinâmica de sistemas de pisos mistos. / [en] Over the years the steel-concrete interaction have been achieving excelent results, in terms of structural performance. This fact have enlarged the range of applications of concrete and steel structures enabling the development of efficient solutions that attend the demands claimed by the market and by increasinly daring architectures. The composite action main objective is to combine steel and concrete into single structural system where the optimum performance of the combined elements could be explored. The concrete is used to sustain compressive while the steel is better used when submitted to tension. These singular characteristics of the composite systems, on the other hand, lead to composite structural systems with natural frequencies close to the frequency associated to human induced loads. Usually the design of composite structures is focused on verifications related to ultimate limit states associated to strength and stability, but the problems related to serviceability limit states should also be carefully considered. Despite the fact that floor vibration induced by human activity has been extensively investigated in the past (1828-2009) there is still a lack of published information on theoretical-experimental correlations on the dynamic response of composite structures specially after considering effects releted to partial interaction, orthotropy and semi-rigid connections. The present study has the objective of contributing in the direction of better understand the effect of the steel-concrete interaction on the composite floor system dynamic response.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A comunidade científica tem conhecimento de que uma das etapas mais relevantes no projeto de estruturas de aço e mistas, diz respeito a uma avaliação precisa sobre os modelos estruturais que representam o comportamento real das ligações viga-coluna. Este assunto tem sido objeto de vários trabalhos de pesquisa nas ultimas décadas. Na prática corrente do projeto de estruturas de aço, a grande maioria das ligações viga-coluna é representada por modelos flexíveis (rótulas) ou rígidos (engastes). Contudo, na maior parte dos casos práticos, essas ligações assumem um comportamento intermediário, ou seja, semi-rígido. Um outro ponto importante acerca do assunto diz respeito à avaliação da resposta dinâmica de estruturas de aço com a consideração pertinente do efeito das ligações, especialmente, no que tange as semi-rígidas, já que a maioria dos trabalhos de pesquisa concentra-se apenas no estudo da resposta estática dos modelos. Assim sendo, esta investigação apresenta uma contribuição inicial no que tange ao emprego de elementos que representem mais fielmente os efeitos das ligações estruturais na análise dinâmica de estruturas de aço, evidentemente, com a consideração do efeito de semi-rigidez dessas ligações. Desta forma, este trabalho de pesquisa propõe o uso de um modelo mecânico com elementos de mola rotacionais não-lineares, objetivando simular adequadamente o efeito das ligações viga-coluna especificamente em pórticos de aço. Inicialmente, foi feita uma calibração do modelo computacional desenvolvido, comparando os resultados obtidos mediante o uso do modelo de mola rotacional com os dados obtidos na literatura técnica sobre o assunto. Na seqüência, desenvolve-se uma analise paramétrica extensa, com a inclusão de todos os efeitos mencionados no parágrafo anterior, de forma a avaliar mais detalhadamente a resposta dinâmica dos pórticos de aço, deslocamentos e esforços, com base no estudo de um edifício residencial de quatro pavimentos. / The scientific community has realized that one of the most relevant stages in the design of steel and composite structures concerns to an accurate evaluation about the structural models that represent the actual behaviour of the beam-to-column connections. This issue has been the subject of many studies over the last decade. In the current design of steel structures, most of the beam-to-column connections are represented by pinned or rigid models. However, in most of the current cases, the connections have an intermediate behaviour between these two cases. Another important issue about the correct evaluation of the dynamic response of steel structures its about the consideration of the effects of the joints, especially of the semi-rigid joints, since most of the studies consider only a static analysis of the models. Therefore, this dissertation has proposed the use of a mechanical model of rotational springs with a nonlinear behaviour, objectifying a proper simulation of the beam-to-column effects in steel frames. The numeric results were obtained along the present study, and calibrated based on many computer models available on the literature. On the sequence, a large parametric analysis is developed, including all the effects mentioned before, objectifying evaluate more precisely the dynamic response of the steel frames (displacements and forces), based on the static and dynamic response of a four storey edifice.

Made available in DSpace on 2016-06-02T20:09:04Z (GMT). No. of bitstreams: 1 DissASS.pdf: 3030488 bytes, checksum: a4d23b016b1767d42942fdad295c0fe1 (MD5) Previous issue date: 2006-09-01 / Universidade Federal de Minas Gerais / The behaviour of reinforced concrete precast beams is strongly influenced by the flexural stiffness of its beam-column connections, wherein there is interdependence between the nonlinearity of the moment-curvature relationship along the beam and the non-linearity of the moment-rotation relationship of the beam-column connections. In most of the existing researches on semi-rigid connections in precast structures, the main focus lays on the characterization of the flexural stiffness by performing experimental tests on isolated models of beam-column connections instead of tests on sub-frames, comprising beam and connections. In this research an experimental procedure was developed, wherein different theoretical equations based on the fixity factor of the connections were combined, allowing the integration between the stiffness of the reinforced concrete beam with the flexural stiffness of the beam-column connections. Therefore, by using this procedure it was possible to evaluate the semi-rigid behaviour of the beam-column connection, highlighting the possibility of carrying out just one test for the precast beam with its connections. The analyses of the experimental results indicate that the studied connection was capable of absorbing around 53% of the elastic beam-end moment at the ULS, compared with the situation of a full restrained connector, implying the increase of 170% of the positive mid-span moment of the beam. This level of semi-rigid behaviour for the beam-column connection can affect the global stability of skeletal precast concrete structures with more than five storeys in height. For this reason, the present research shows the need for further studies with the purpose of enhancing the analysis and the design of precast concrete structures for multi-storey buildings. / O comportamento das vigas pré-moldadas de concreto armado é fortemente influenciado pela rigidez à flexão das ligações viga-pilar, existe uma interdependência entre a não linearidade da relação momento-curvatura ao longo da viga pré-moldada com a não linearidade da relação momento-rotação nas ligações viga-pilar. A maioria das investigações experimentais existentes sobre ligações semi-rígidas em estruturas pré-moldadas, tanto na literatura nacional quanto internacional, têm enfatizado seus estudos na caracterização da rigidez à flexão de maneira isolada, não realizando ensaios do comportamento conjunto das vigas pré-moldadas com as suas ligações. Desenvolve-se nesta pesquisa um procedimento experimental onde se procurou integrar diversos equacionamentos teóricos com base no fator de restrição aos giros na ligação, os quais permitiram integrar parâmetros de rigidez da ligação e da viga. Desta forma, com base nos resultados experimentais em um único ensaio de um modelo de viga com ligações viga-pilar, foi possível se estimar o engastamento parcial nas ligações viga-pilar. A partir dos resultados experimentais, a ligação viga-pilar foi capaz de absorver cerca de 53% dos momentos elásticos na extremidade da viga, havendo assim um acréscimo de 170% no momento positivo no centro da viga para a situação de projeto no ELU. Este engastamento parcial pode afetar sensivelmente a estabilidade global de estruturas pré-moldadas com mais de 5 pavimentos. Por esta razão, o presente estudo aponta para a necessidade de mais pesquisas nesta área, com o objetivo de possibilitar projetos mais adequados e seguros de estruturas pré-moldadas em esqueleto para múltiplos pavimentos.

Made available in DSpace on 2016-06-02T20:09:05Z (GMT). No. of bitstreams: 1 DissMNK.pdf: 4268420 bytes, checksum: 50c2feaa3b1252323d08d023d64588ae (MD5) Previous issue date: 2007-02-26 / Universidade Federal de Minas Gerais / The present research deals with the study of continuity in slab-beam-column connections in precast concrete structures, wherein an experimental investigation about the contribution of longitudinal reinforced bars, passing on the side of the column in the top of the slab, on the connector flexural stiffness. For this study, a beam-to-column connection was selected, comprising concrete corbel with dowel bars and continuity reinforced bars passing trough the column and fulfilling of grout in the interface of the connection. Two tests were carried out for the characterization of the moment-rotation relationship of two different connection prototypes, one with 100% of the continuity reinforced bars passing trough the column and another with 50% trough the column and 50% in the laterals. The experimental results indicate that bars passing on both sides of the column enhanced the moment-rotation relationship for the second prototype, being even more significant for the serviceability stage. However, rotations at the beginning of plasticization of the moment-rotation curve were close for the two prototypes. The results indicate that the transverse reinforcement between the slab and the beam was capable of mobilizing the external longitudinal bars at the same time of the internal longitudinal bars, passing through the column. Additionally, this reinforcement arrangement provided an increase of the cracking control within the connection zone at the end of the beam / No presente trabalho foi estuda a continuidade em ligações laje-viga-pilar em estruturas pré-moldadas de concreto com a realização de uma investigação experimental quanto à contribuição da parcela de armadura passante nas laterais do pilar na capa da laje, tanto para a rigidez à flexão quanto para o controle da fissuração. Para objeto de estudo, selecionou-se uma ligação viga-pilar com consolo de concreto e chumbador, com armadura de continuidade passante no pilar por meio de bainhas lisas preenchidas com graute. Foram realizados ensaios para a caracterização das ligações com dois modelos experimentais, sendo um com 100% da armadura de continuidade passando dentro do pilar e o segundo com 50% dentro do pilar e 50% nas laterais. Os resultados experimentais mostraram que as barras laterais ao pilar contribuíram para aumento da rigidez à flexão, principalmente para a fase de serviço, inferior à carga de projeto. Entretanto, as rotações relativas ao início da plastificação da relação momento-rotação foram próximas para os dois modelos. Acredita-se que o detalhamento empregado para armadura de costura entre a viga e a laje permitiu que as armaduras longitudinais dentro e fora do pilar fossem mobilizadas de forma conjunta, tanto na fase de serviço quanto para a fase de projeto, promovendo um controle efetivo da fissuração na região da ligação