A análise de painéis de concreto armado submetidos a corte puro é um tópico que tem recebido atenção de pesquisadores ao longo dos anos. Isto se deve, principalmente, à dificuldade encontrada na aplicação do carregamento e das condições de vinculação sobre a estrutura. Esta dificuldade é constatada tanto experimentalmente como na análise numérica. O objetivo deste trabalho é apresentar um modelo numérico para simular o comportamento de painéis de concreto simples e de concreto armado submetidos ao corte. Na análise computacional via Elementos Finitos, será utilizado um modelo de fissura incorporada que considera a contribuição da armadura no equilíbrio interno de forças do elemento. Estes modelos se baseiam no conceito de descontinuidades incorporadas dentro de elementos finitos padrão. O modelo incorporado implementado é uma continuação dos trabalhos desenvolvidos por d’Avila (2003) e Brisotto (2006), baseados no modelo de Dvorkin, Cuitiño e Gioia (1990). O modelo de transferência de tensão por aderência de Russo, Zingone e Romano (1990) foi usado por d’Avila para incluir a contribuição da armadura no equilíbrio interno de forças do elemento. Para representar as barras de aço da armadura, é utilizado o modelo incorporado desenvolvido por Elwi e Hrudey (1989) que permite a disposição arbitrária das barras no interior dos elementos de concreto. Os resultados dos ensaios numéricos de painéis de concreto armado submetidos ao corte puro com diferentes taxas de armadura são comparados com os resultados experimentais apresentados por Vecchio (1981). São incluídos dois diferentes modelos de efeito de pino (resistência ao corte das barras da armadura), analisando-se a influência dos mesmos no comportamento dos painéis ensaiados. O efeito do engrenamento dos agregados na fissura também foi estudado. Vários painéis com diferentes formas de ruptura experimental foram simulados, obtendo-se respostas muito boas para a maioria deles. Comparações da resposta tensão tangencial x distorção com e sem efeito de pino foram feitas, verificando-se a grande importância deste efeito na resposta global. / The analysis of reinforced concrete panels submitted to in-plane shear has received the attention of researchers along the years. It is mainly due to the difficulty to simulate the application of the external loads and the structural boundary conditions. The purpose of this work is to present a numerical model to represent reinforced concrete panels submitted to inplane shear. In the computational analysis via Finite Elements, an embedded crack model that considers the inclusion of the reinforcement contribution in the internal force equilibrium of the element is presented. This type of model is based in discontinuities embedded into standard finite elements. The implemented formulation uses the model presented by Dvorkin, Cuitiño and Gioia (1990), which does not have the reinforcement contribution in the element internal equilibrium. The adherence stress transfer model of Russo, Zingone and Romano (1990) is used to include this reinforcement contribution. An embedded model was employed to represent the reinforcement bars, allowing that they can be placed in an independent position and shape in the FEM elements. The numerical results are compared with Vecchio’s work. Also are included two different dowel action models (transversal shear resistance of the bars) and is studied their influence in the panels’ behavior. Panels with different experimental rupture modes were simulated with good responses in the most cases. Comparisons of shear stress x shear strain curve with and without dowel action are performed, showing the importance of this effect on the global response.

O trabalho tem por finalidade o estudo teórico e experimental de ligações em estruturas de madeira com cavilhas de madeira de seção cilíndrica impregnadas com resinas estirênicas. A impregnação da madeira tem como objetivos: diminuir o processo de degradação, retardação ao fogo, melhorar a estabilidade dimensional e aumentar as propriedades de resistência e elasticidade da madeira. Foram determinados experimentalmente as características de resistência e elasticidade do material e posteriormente realizados ensaios de ligações padronizados com solicitação paralela e normal às fibras. Os resultados dos ensaios mostram aumento na resistência de compressão normal até 292% e aumento de 80% no limite de proporcionalidade da ligação. A madeira utilizada para a impregnação foi o Pinus de reflorestamento. / The aim of this work is a theorytical and experimental studies of joints in timber structures with wooden dowels of circular cross section impregnated with styrenic resins. The objetives of wood impregnation are to decrease the deterioration process, to promote fire retardation, to improve dimensional stability and mainly increase the compression strength and stiffiness of wood. The strength and stiffness properties of the material are determined. Standard joints tests are carried out in compression both parallel and perpendicular to grains. The test results increases of compression perpendicular strength up to 292% and the up to 80% proportional limit joint. The wood used for impregnation was Pinus from reforestation sites.

Joints are critical parts of timber structures, transmitting static and dynamic forces between structural members. The ultimate behavior of a loaded building depends strongly on the structural configuration and the capacity of the joints. The collapse of a whole building or less extensive accidents that may occur is usually starting as a local failure inside or in the vicinity of a joint. Such serious failures have recently occurred in our Nordic countries. Especially the collapse of two large glued laminated timber structures clearly indicates the need of an improved joint design. The trend toward larger and more complex structures even further increases the importance of a safer design of the joints. An aim of this partly experimental and partly numerically based thesis has been to investigate if steel-to-timber dowel joints are affected by moisture-induced stresses. The experimental results showed that the load-bearing capacity of the joints is reduced by such a moisture influence. Most of the decrease in load-bearing capacity observed was found in joints initially exposed to restrained shrinkage deformations caused by the presence of dowel fasteners in the joint area. The load-bearing capacity was, however, also found to decrease in joints exposed to an initial decrease in moisture without any fasteners present in the specimens during storage before loading. An explanation of this unexpected behavior is that moisture gradients cause tensile stresses. It is shown by numerical simulations that the moisture-induced stresses are so large that they may have a considerable influence on the joint behavior. Use of contact-free measurement methods, used in some of the experimental tests, was in many ways found to be superior to traditional measurement techniques, but was also found to be a valuable complement to the numerical analysis performed. From numerical results obtained in combination with results from contact-free measurements several observations of considerable interest were made. For dowel-type joints loaded in tension parallel to the grain a strongly non-uniform strain distribution was found in the joint area. It was further observed that the shear and tensile strains were concentrated close to the fasteners in the joint area. These concentrations will influence the failure mode of the joint. A general observation was that the larger sized joints failed in a brittle manner. Keywords: constraint stresses, contact-free measurement, dowel-type joints, humidity variations, moisture-induced deformations, timber structures

Internationellt sett är merparten av de dammbrott som ägt rum kopplat till grundläggningen. Det är oftast kopplat till att det finns osäkerhet i de rådande grundförhållandena. Som extra säkerhet, installerades bergförankringar som en åtgärd att behandla osäkerheterna i de rådande grundförhållandena. I Sverige är merparten av kraftverksdammarna uppförda mellan 1940-och1960 talet. Det var inte ovanligt att cementingjutna slakarmerade kamstål sattes under dammarna som en extra säkerhet. När dessa bergbultar installerades var kunskapen om dess verkningssätt begränsat, då teorier om bergbultens verkningssätt började utvecklas under 70- och 80-talet. Vid dimensionering av bergförankring till dammbyggnader i nutid tillämpas RIDAS, Kraftföretagens riktlinjer för dammsäkerhet, som är upprättade av de Svenska dammägarna. I RIDAS framgår att när det endast föreligger en risk för glidning får rostfri slak armering användas som bergförstärkning och dimensioneras enligt BBK, Boverkets handbok för betongkonstruktioner, kap 3.11 "kraftöverföring genom fog". Examensarbetets inledande del är en litteraturstudie som är inriktad på den forskning som har bedrivits rörande bergbultens principiella beteende när den går till brott. Vidare i litteraturstudien har en beräkningsteori som utvecklats av Holmberg (1991) vilken beskriver en bergbults bidrag till bärförmågan för en bergspricka studerats i detalj. Teorin har även jämförts mot experimentellt utförda skjuvförsök av bergbultar. Med hjälp av den teori som presenterades i litteraturstudien genomfördes en stabilitetsanalys av en betongmonolit i utskovsdammen på en typisk Svensk vattenkraftstation. Målet var att undersöka möjligheten för bergbultarna, som är installerade i berggrunden att samverka, med ett antaget horisontell sprickplan under dammbyggnaden. Det bidrag till bärförmågan som bergbultarna och bergsprickan utgör till totalstabiliteten jämförs med de krav som ställs i RIDAS. I slutet av arbetet förs en diskussion om de presenterade teoriernas förmåga att beskriva bultens bärförmåga under olika förhållanden samt hur en bergförankring bör utformas för att säkerställa dragbrott i bulten. Efter det ges förslag på forskning rörande bergbultning som kan utföras, för att bättre förstå bergbultens principiella beteende. / Internationally, the majority of dam failures that have occurred are related to the foundation. It is usually linked to the large uncertainty in the actual propertys of the foundation. A common measure was to install rock bolts as an extra precaution in the subgrade to handle the uncertainties of the subgrade. In Sweden, most of the hydroelectric dams were constructed between 1940 and 1960. It was not uncommon that cemented reinforced rock bolts were installed in the subsoil as an extra precaution. When these rock bolts were installed, understanding of their stress handling was limited, considering the fact that the theory of the rock bolts behavior was first studied between 1970 and 1980. The first part of this thesis is a thorough review of the literature which focuses on the research that has been conducted on the fundamental behavior of the rock bolt when it fails. In this study, a computational theory describing a rock bolts load contribution to a rock joint is presented, verified against experimental shear tests performed on rock bolts. In the design of rock anchoring to the construction of reservoirs in the present application RIDAS, Power Companies' guidelines for dam safety, the guidelines is formed by the Swedish dam owners. Accordingly to RIDAS where there is only a risk for a slide in a rock joint stainless untensioned rock bolts are allowed to be used fore support and dimension according to BBK, Boverkets handbok för betongkonstruktioner, kap 3.11 "kraftöverföring genom fog". Using the theory presented in the literature review, a stability analysis of a monolith on Långbjörn PowerStation was carried out. The goal was to explore the possibility of rock bolts installed in the subgrade to interoperate with a rock joints under the dam building. The load contribution of rock bolts and the rock joints has to overall stability is compared with the requirements of the Swedish power company’s guidelines for dam safety, RIDAS. At the end of the thesis, the presented theories’ applicability under different conditions and how a rock anchor should be designed to be as efficient as possible is discussed. In conclusion, suggestions for research that can be performed on bolting, to gain better understanding of the fundamental behavior of the rock bolt are presented.

The embedment behavior of dowels in timber structures, as an essential parameter in the design of connections, is the subject of this thesis. There are numerous advantages using timber structures, including sustainability, energy efficiency, and aesthetic appeal. The mechanical performance of connections in timber structures can be affected by environmental variables, such as moisture content. Thus, in the thesis the embedment behavior of dowels in timber, including the embedment strength and elastic and plastic stiffness at various moisture levels was investigated. In addition to different moisture contents, the effects coming along with changing the moisture content, like swelling and shrinkage, in combination with the assembly history were studied. The study investigated the effects of moisture content variations on the embedment behavior of dowels in timber loaded perpendicular to the grain at relative humidity levels of 38%, 65%, and 85% at a temperature of 20◦C. The study also explored the impact of assembly history of the steel dowels on the embedment behavior. The expression ”assembly history” refers the effects of drilling and assembling steel dowels at different times, i.e. if drilling the timber occurs before changing the moisture content or after changing the moisture content.  Full-hole embedment tests were conducted in five different series to cover all three levels of moisture content while taking the assembly history into account. In total, 100 embedment experiments were carried out, with 50 samples of spruce and 50 samples of birch being assessed perpendicular to the grain. In addition, 20 solid timber specimens were exposed to cyclic loading to evaluate the embedment behavior under these conditions. To evaluate the stress on the timber around the dowel, finite-element simulations, using linear-elastic material behavior in combination with volumetric changes due to moisture variation were conducted. Corresponding to the assembly history in the experiments, the situations of moisture variation in presence and absence of the steel dowel for the swelling and shrinkage case were investigated. The experimental results showed that while the elastic and plastic embedment stiffness can be impacted by moisture content only in low MC situations, it can potentially affect embedment strength in both dry and wet conditions. Additionally, the assembly history influences only the plastic stiffness in a low MC condition. Results from cyclic loading have shown no significant difference to embedment strength and stiffness gained from monotonic loading. According to numerical simulations, the tensile normal stress in the direction perpendicular to the load direction is higher than the tension strength for the shrinkage case with the dowel present. This might be explained by using a simple linear elastic material model in the FEM simulation, which causes an overestimation in the stiffness properties. In conclusion, this thesis offers new perspectives and a deeper knowledge of how moisture content, assembly history, and cyclic loading perpendicular to the grain affect the embedment behavior of dowels in timber connections.

Made available in DSpace on 2014-07-29T15:03:36Z (GMT). No. of bitstreams: 1 pre_text fabio reis engcivil.pdf: 737129 bytes, checksum: ed254364f2d9e0fc110774d49fe0fc6e (MD5) Previous issue date: 2009-06-26 / The use of concrete pavements in highways is a valuable alternative to obtain a surface with high durability and low maintenance. This type of pavement has the performance compromised by fissures, especially when they occur in the joint with greater vulnerability of the concrete pavement. This work presents a study of the effectiveness of sawed joints in concrete pavements where eleven plates were tested until failure. The variables were: length of circular dowels (200 mm, 300 mm, 400 mm and 500 mm), dowel diameter (10 mm and 16 mm) and type of concrete (conventional and self-compacting). The tests were performed on the concrete plates supported on a base composed of sheets of rubber. A line load was placed on one side of the joint. The test results showed that the use of transfer dowels contributes significantly to the efficiency of the concrete pavements and increasing the length and the diameter of the circular dowels improves efficiency; 10 mm diameter dowels are not compatible with 120 mm thick concrete pavements, but 16 mm dowels bars present good performance; the use of reduced dowel bar lengths below 40 mm is not recommended; pavements with conventional concrete have better performance in the joints due to better aggregate interlocking that the conventional concrete of this search present, when compared the self-compacting concrete; dowels bars with reduced length did not reach yielding, characterizing an incomplete use of steel dowels because the transfer energy its over before the yielding of steel dowels / A utilização de pavimentos de concreto simples em rodovias mostra-se como uma valiosa alternativa na obtenção de um pavimento com grande durabilidade e pouca manutenção. Esse tipo de pavimento tem o seu desempenho comprometido com o surgimento de fissuras, principalmente quando as mesmas se apresentam em sua junta, região de maior vulnerabilidade do pavimento de concreto. Dessa forma este trabalho apresenta um estudo da eficiência da junta serrada em pavimentos de concreto simples onde foram ensaiadas onze peças cujas variáveis foram: comprimento da barra de transferência (200 mm, 300 mm, 400 mm e 500 mm), diâmetro da barra de transferência (10 mm e 16 mm) e tipo de concreto (convencional e autoadensável). Os ensaios foram realizados com o posicionamento das peças de concreto sobre uma base composta de placas de borracha e aplicada uma carga estática distribuída em um lado da junta por toda sua extensão, sendo interrompido o carregamento somente após a ruptura da peça. Os resultados da pesquisa mostraram que: a utilização de barras de transferência contribui significativamente para a eficiência do pavimento e com o aumento do comprimento e do diâmetro da barra, ocorre uma melhora na eficiência; barras de 10 mm de diâmetro não são compatíveis com pavimentos de concreto de 120mm de espessura, mas as barras de 16 mm apresentam bom desempenho nessa espessura; a utilização de comprimentos reduzidos de barras abaixo de 400 mm não é recomendada; peças de concreto convencional apresentam um melhor desempenho nas juntas, provavelmente em função do melhor intertravamento dos agregados que o concreto convencional desta pesquisa apresentou, quando comparado ao concreto autoadensável; barras de aço de comprimento reduzido não atingem o escoamento, caracterizando uma não utilização completa do aço pois a transferência de esforços foi cessada sem o aço da barra de transferência escoar.

Le comportement de l’interface acier-béton a une grande importance lorsque la fissuration des structures en béton armé est étudiée. Une approche par éléments finis a été proposée par (Torre-Casanova, 2013) et (Mang, 2016) pour représenter l'interface acier-béton dans les simulations de structures à grandes dimensions Le modèle proposé permet de calculer le glissement tangentiel entre l'acier et le béton. L’objectif de cette étude est d’améliorer ce modèle initial pour le rendre plus efficace et plus représentatif. Le document est découpé en trois parties : 1) Le modèle initial de liaison est évalué. Puis amélioré tant en chargement monotone qu’alterné. Le nouveau modèle est validé par plusieurs applications numériques. 2) L'effet de confinement est implémenté dans le modèle de liaison acier-béton. L'effet sur le comportement structural du confinement actif est étudié en utilisant le nouveau modèle. A partir des simulations proposées, il est montré, par l’utilisation du nouveau modèle, que l’effet de confinement actif peut jouer un rôle sur les comportements monotone que cyclique. 3) L'effet goujon est étudié avec le nouveau modèle liaison acier-béton. Deux campagnes expérimentales différentes sont simulées avec différents modelés de renforts (1D barre et poutre) et d’interface (liaison acier-béton et liaison parfaite). Les résultats montrent que le nouveau modèle de liaison acier-béton permet de mieux reproduire les résultats expérimentaux par rapport au modèle de liaison parfaite aux échelles globale et locale. / In numerical applications of reinforced concrete structures, the steel-concrete interface behavior has a vital importance when the cracking properties are investigated. A finite element approach for the steel-concrete interface to be used in large-scale simulations was proposed by (Torre-Casanova, 2013) and (Mang, 2016). It enables to calculate the slip between the steel and concrete in the tangential direction of the interface element representation. The aim is here to improve the initial bond-slip model to be more efficient and more representative. The document is divided into three parts: 1) The existing bond-slip model is evaluated. The bond-slip model is then improved by considering transversal and irreversible bond behaviors under alternative loads. The new bond-slip model is validated with several numerical applications. 2) Confinement effect is implemented in the bond-slip model to capture the effect of external lateral pressure. According to the performed numerical applications, it is demonstrated how the active confinement can play a role, through the steel-concrete bond, during monotonic and cyclic loading cases. 3) Dowel action is finally investigated with the new bond-slip model. Two different experimental campaigns (Push-off tests and four-point bending tests) are reproduced with different reinforcement (1D truss and beam) and interface (new bonds-slip and perfect bond) models. The results show that the proposed simulation strategy including the bond slip model enables to reproduce experimental results by predicting global (force-displacement relation) and local behaviors (crack properties) of the reinforced concrete structures under shear loading better than the perfect bond assumption which is commonly used in the industrial applications.

No description available.

Este trabalho apresenta desenvolvimentos na modelagem mecânica de estruturas de barras em concreto armado, bem como no acoplamento entre modelos de confiabilidade e otimização do tipo RBDO para obtenção de dimensões ótimas, respeitando os requisitos de segurança especificados em projeto. Quanto à modelagem mecânica via Método dos Elementos Finitos (MEF), além do comportamento não-linear geométrico e dos materiais, foi considerada a contribuição dos mecanismos complementares de resistência ao cisalhamento, dados pelo engrenamento de agregados e efeito de pino das armaduras longitudinais. Além disso, um modelo simplificado que avalia a contribuição da armadura transversal também foi proposto. Foi desenvolvida uma formulação de otimização que deixa a posição da linha neutra livre, ao contrário de formulações existentes. Esta formulação resultou em projetos mais economicos dos que aqueles encontrados na literatura. Na questão do acoplamento de confiabilidade e otimização, foram exploradas melhorias no Método de Superfície de Resposta e no acoplamento direto via Método de Confiabilidade de Primeira Ordem e Técnica dos Gradientes Numéricos. Estas resultaram em maior precisão dos resultados e aumento na velocidade de convergência. Os modelos mecânicos, incluindo análise não-linear e mecanismos complementares, a formulação de otimização e as técnicas de confiabilidade foram implementados em um programa computacional para dimensionamento ótimo de elementos em concreto armado. O programa foi utilizado na resolução de vários problemas-exemplo. Verificou-se que a consideração dos mecanismos complementares de resistência ao cisalhamento produziram acréscimo na carga última, quando comparadas com as respostas sem tais efeitos. Verificou-se também que os mesmos mecanismos produziram um aumento, até mais significativo, nos índices de confiabilidade obtidos. As dimensões ótimas de elementos estruturais também foram comparadas, considerando-se modelos lineares e não-lineares dos materiais. O estudo mostrou que os custos da estrutura otimizada são menores, quando se considera os efeitos de comportamento não-linear dos materiais. / This work presents some developments in the mechanical modeling of reinforced concrete bar structures, as well in the coupling of reliability and RBDO optimization models, with the purpose of obtaining optimal dimensions considering the safety requirements specified in design. As for the mechanical modeling via Finite Element Method (FEM), in addition to geometrical and material nonlinear behaviors, the contribution of shear resistance complementary mechanisms (aggregate interlock and dowel action of longitudinal reinforcement) was taken into account. Moreover, a simplified model that evaluates the contribution of shear reinforcement was also proposed. In an improvement of existing formulations, an optimization scheme was developed which leaves the position of the neutral axis free. This improvement resulted in more economical cross-sections, than those found in the literature. With respect to the coupling of reliability and optimization methods, improvements were sought in the Response Surface Method and in the direct coupling via First Order Reliability and Numerical Gradients methods. These improvements resulted in greater precision and in increased convergence speed. The mechanical models, including non linear effects and complementary mechanisms , the optimization and reliability formulations were implemented in a computational code for the optimum design of reinforced concrete structures. The program was used to solve a number of example problems. It was found that the complementary mechanisms resulted in an increase of ultimate loads, when compared to the response obtained without these effects. These mechanisms also resulted in an even greater increase of the elements reliability. Optimal dimensions of the structural elements were also compared, considering linear and non-linear material models. The cost of the optimum structure was found to be smaller when non linear effects are taken into account.

Joints are critical parts of timber structures, transmitting static and dynamic forces between structural members. The ultimate behavior of e.g. a building depends strongly on the structural configuration and the capacity of its joints. The complete collapse of a building or other less extensive accidents that may occur usually start as a local failure inside or in the vicinity of a joint. Such serious failures have recently occurred in the Nordic countries. Especially the collapses of two large glued-laminated timber (glulam) structures clearly indicate the need of an improved joint design. The trend toward larger and more complex structures even further increases the importance of a safer design of the joints. One aim of this partly experimentally and partly numerically based work has been to investigate if the short term capacity of steel-timber dowel joints loaded parallel to the grain is affected by an initial drying exposure. The experimental results showed that the load-bearing capacity of the joints is indeed reduced by such moisture changes. Moisture induced stresses was mentioned to be the explanation. The key point is that the climates chosen in the present work (20°C / 65% RH and 20°C / 20% RH) are equivalent to service class 1 according to EC5 (Eurocode 5 2004). Thus, EC5 predicts no decrease in load-bearing capacity, in relation to the standard climate used during testing. A decrease in load-bearing capacity in the range of 5-20%, which was found in the present work, is of course not negligible and, therefore, there could be a need to introduce the effect of drying in design codes. Because similar results were also observed for a double-tapered glulam beam, further work should consider timber structures in general. Two numerical methods in order to predict the capacity of multiple steel-timber dowel joints loaded parallel to the grain were tested in the thesis. For the first method, where fracture mechanics (LEFM) concepts were implemented, a good correlation with the experimental results was seen. Also for the second method, where the capacity for a single dowel-type joint as given in EC5 was used as a failure criterion, a good correlation to traditional EC5 calculations of multiple dowel-type joints was seen. One advantage of using numerical methods in design is that the capacity of the joint can be calculated also for cases when the dowels are placed in more complex patterns. From both a structural and an architectural point of view this can be very important. In addition, such numerical methods are effective tools for the structural engineer when considering complicated loading situations in joints, i.e. eccentric loading giving moments in the joint.