[pt] A busca por soluções geotécnicas que aumentem a vida útil das estruturas e também possam economizar material natural levou ao desenvolvimento de produtos conhecidos como geossintéticos. Dentre as várias famílias de geossintéticos, foram criados elementos que funcionassem como reforço de base-subleito em pavimentos na condição de subleito muito deformável, denominadas geogrelhas. O presente trabalho teve o objetivo de analisar o comportamento mecânico de uma estrutura de pavimento reforçado com geogrelha, submetida à aplicação de carregamento cíclico e à variação de umidade do material do subleito. Foi utilizado para o desenvolvimento dos ensaios um modelo físico de verdadeira grandeza no qual foi construída a estrutura do pavimento composta de um subleito de 100 cm de espessura e uma camada de base de brita de 20 cm de espessura. Nesta estrutura analisou-se o efeito da inserção do geossintético como reforço de camada de base e a variação da umidade do subleito. As medidas fornecidas pelos transdutores de deslocamentos (LVDTs) foram os parâmetros de comparação entre a estrutura de pavimento com e sem reforço no decorrer dos ensaios. Os refletômetros no domínio do tempo (TDRs) monitoraram a variação da umidade do subleito. A comparação entre os deslocamentos da estrutura reforçada e não reforçada permitiu determinar a influência do reforço mostrando-se eficiente na redução dos deslocamentos superficiais verticais. A utilização de equipamentos portáteis para avaliar o comportamento mecânico do pavimento in situ mostraram ser uma ferramenta recomendável para estudos defletométricos de forma pontual no pavimento. / [en] The search for geotechnical solutions that increase the life time of structures and can also reduce the use of natural materials carried out to the development of products known as geosynthetic. Among the various families of geosynthetics, have been created elements which function as reinforcement of base-subgrade of pavements when the condition of the subgrade is very deformable, called geogrids. This study had the objective to analyze the mechanical behavior of a structure of geogrid reinforced pavement, submitted to the application of cyclic loading and variation in subgrade layer moisture. It was used for the development of tests a true scale physical model, in which was built a structure of pavement composed of a subgrade with 100 cm of thickness and a gravel layer of 20 cm of thickness. In this structure has been analyzed the effect of insertion of geogrid like base layer reinforcement and a variation in subgrade layer moisture. The measures provided by the displacement transducers (LVDTs) were the parameters of comparison between a structure of pavement with and without reinforcement during the tests. The Time Domain Reflectometry (TDR) monitored the variation of moisture from the subgrade. The comparison between the displacements of reinforced and unreinforced structure allowed determine the influence of reinforcement showing to be efficient to reduce superficial vertical displacements. The use of mobile devices to evaluate the mechanical behavior of the pavement in situ proved to be a tool recommended for punctual studies on pavements.

Bracing members are considered to be effective earthquake-resistant elements as they improve the lateral strength and stiffness of the structural system and contribute to seismic energy dissipation by deforming inelastically during severe earthquake motions. However, the cyclic behavior of such bracing members is quite complex because it is influenced by both buckling and yielding. This thesis presents simple but an efficient analytical model that can be used to simulate the inelastic cyclic behavior of steel braces. This model achieves realism and efficiency by combining analytical formulations with some semi-empirical formulas developed on the basis of a study of experimental data. A brace is idealized as a pin-pin ended member with a plastic hinge located at mid-length of a brace Input parameters of the model are based on only material properties such as steel yield strength and modulus of elasticity as well as geometric properties including cross-sectional area, moment of inertia, etc. The obtained results are verified by the experimental and available analytical results.

Este trabalho consiste em um estudo do comportamento de nós de pórtico de ligações viga-pilar de concreto armado submetidos a ações cíclicas. O trabalho é composto por duas etapas: uma de investigação experimental e outra de cunho teórico. A etapa experimental teve como base os ensaios realizados em cinco modelos físicos de ligações viga-pilar. Os resultados desses ensaios permitiram a observação de diversos aspectos do comportamento estrutural dos nós de pórtico frente às ações cíclicas e a avaliação da influência de algumas variáveis. Neste trabalho, as variáveis escolhidas foram a variação do carregamento aplicado e o detalhamento da armadura transversal na região do nó. Os principais efeitos das ações cíclicas sobre as cinco ligações ensaiadas foram: aumento generalizado dos deslocamentos globais, perda de resistência e de rigidez dos elementos estruturais, propagação e aumento da abertura das fissuras inicialmente formadas, tendência de uniformização das deformações dos estribos do nó ao longo dos ciclos e maior deterioração do nó de pórtico em relação aos elementos viga e pilar. Na etapa teórica, foram empregados essencialmente dois tipos de modelos: i) modelos derivados das idealizações dos modelos clássicos de biela e tirante. ii) modelos simplificados que empregam conceitos da Mecânica do Dano e da Fratura, para a avaliação dos efeitos de perda de rigidez (dano) e das deformações permanentes (plasticidade) na resposta global da ligação viga-pilar. Por fim, foram feitas comparações entre os resultados experimentais e teóricos, chegando-se a importantes conclusões sobre o comportamento mecânico do nó frente às cargas cíclicas e sobre a eficiência dos modelos teóricos em simular a resposta do nó de pórtico e da ligação como um todo. As comparações mostraram que, dentro de certos limites, os modelos teóricos fornecem resultados satisfatórios frente aos resultados experimentais / The present thesis studies the behavior of frame joints in reinforced concrete beam-column joints subjected to cyclic loads. The thesis is divided into two parts: an experimental study and a theoretical-based study. The experimental study is based on laboratory tests on five physical models of beam-column joints. The results of this experimental study permitted the observation of various aspects of the structural behavior of frame joint subjected to cyclic load and estimating the influence of certain variables the affect the behavior of such joints. In the present thesis, the variables studied are the applied load and reinforcement detailing at the joint location. The effects of cyclic loads on the tested joints were: an increase in the overall deformation, loss of strength and stiffness of structural elements, crack propagation and increase in crack width of previously formed cracks, a tendency towards a uniform strain distribution in the transverse reinforcement at the joint section and a more rapid deterioration of frame joints compared to beam/column joints. At the theoretical level, two types of models were used to study the behavior of the joint: i) a model derived from the idealization of the classical strut-tie model, and ii) a simplified damage and fracture mechanics-based model for estimating the effects of the loss of stiffness (damage) and permanent strains (plasticity) on the overall response of the beam column joint. To reach any conclusion on the mechanical behavior and the efficiency of existing theoretical models employed in the design of reinforced beam-column joints and other joints subjected to cyclic loading, a comparative study between the theoretical and experimental results was carried out. The results show that within certain limits, the theoretical models employed are in good agreement with experimental results

Fibre-reinforced polymers (FRPs) are becoming increasingly accepted in structural engineering applications. In particular, Carbon-FRP (CFRP) tendons are proving to be promising as prestressing reinforcement for concrete structures. While several studies have been conducted on CFRP-prestressed concrete beams, very little attention has been given to their long-term behaviour at low temperatures. This thesis investigates the behaviour of CFRP prestressed concrete beams in two studies: (a) under sustained loading at low temperature, and (b) under high-cycle fatigue at low temperature. Seven 13 year old, 4.4 m long precast concrete T beams were tested, of which five were prestressed to various levels with CFRP tendons and two with conventional steel strands. In the first study, three beams were exposed to −27 °C while being subjected to a sustained load of 25% of their flexural capacity for 163 days. The sustained load produced cracking in two beams with lower prestress levels. Results were compared to those obtained from three similar beams subjected to the same sustained load at room temperature. Deflection increase under sustained load at low temperature was generally small and similar to that at room temperature. Prestressing strain had a direct relationship with temperature in the CFRP prestressed beams. After being subjected to sustained loading, all seven beams were tested in the second study. Only three of the five CFRP prestressed beams were subjected to cyclic loading, one at −28 °C and two at room temperature, while only one of the two steel prestressed beams was subjected to cyclic loading, at −28 °C. Cyclic loading consisted of 3 million cycles at a frequency of 0.85 Hz. The load range represented 21 to 42% of the flexural capacity of the CFRP prestressed beams and 30 to 60% of that of the steel-prestressed beam. Monotonic tests were run every 1 million cycles. Finally, all seven beams were monotonically loaded to failure. All CFRP prestressed beams survived the 3 million cycles but the steel prestressed beam failed after 185,000 cycles. However, the CFRP concrete bond was weakened by high prestress levels, cyclic loading, and low temperature during sustained loading and loading to failure. This resulted in bond failure at loads ranging from 69 to 91% of the full flexural capacity. Stiffness and camber gradually decreased during cyclic loading. / Thesis (Master, Civil Engineering) -- Queen's University, 2009-12-21 15:16:33.381

[pt] A pasta de cimento classe G é muito utilizada nas operações de cimentação de poços de petróleo, sendo submetida a várias formas de deterioração, afetando sua durabilidade. Duas dessas formas de deterioração que ocorrem nos poços são por carregamento cíclico e temperaturas elevadas. Neste estudo, corpos de prova foram submetidos a ensaios de carregamento cíclicos de 30 por cento, 50 por cento e 70 por cento das tensões de ruptura e a temperaturas elevadas de 100 graus Celsius, 200 graus Celsius, 450 graus Celsius e 650 graus Celsius. A microtomografia computadorizada (microCT) foi utilizada para gerar imagens tridimensionais para observar a estrutura interna do material e, através de uma rotina computacional desenvolvida, avaliar qualitativa e quantitativamente a evolução de poros e fissuras após os ensaios. Primeiramente foi utilizado o software Fiji para aplicação de filtro de redução de ruído, em seguida as imagens de antes e depois dos ensaios são alinhadas com auxílio do software DataViewer. No software Dragonfly os vazios (poros e fissuras) das imagens são segmentadas e quantificados, apresentando o volume e esfericidade dos vazios de interesse. Os resultados dos ensaios de carregamento cíclico mostraram que submeter a 30 por dento da tensão de ruptura quase não influencia na estrutura interna mas 50 por cento e 70 por cento causam danos significativos no material. Os corpos de prova submetidos a 100 graus Celsius e 200 graus Celsius apresentaram pequenas fissuras, mas a estrutura dos poros não mudou. No corpo de prova submetido a 450 graus Celsius muitas fissuras foram observadas. Já no submetido a 650 graus Celsius apresentou um elevado nível de degradação, impossibilitando a realização da microCT após o ensaio. Como conclusão, a pasta de cimento classe G pode ser utilizada para operações com carregamentos cíclicos inferior a 30 por cento da tensão de ruptura e inferior a temperaturas de 200 graus Celsius. Finalmente, a correlação de resultados de testes de DRX, DSC e TGA com as imagens obtidas das microCT mostraram que a desidroxilação do Ca(OH)2 e a degradação do CaCO3 causam alta deterioração para o material em estudo. / [en] Class G oil well cement is frequently used a in oil well cementing operation, which is subjected to various forms of deterioration, affecting its durability. Two of these forms of deterioration is due to cyclic loading and elevated temperatures. In the present study, cylindrical specimens were subjected to cyclic loading of 30, 50 and 70 per cents of the materials ultimate strength and to temperatures of 100 Celsius degrees, 200 Celsius degrees, 450 Celsius degrees and 650 Celsius degrees for one hour. Microcomputed tomography (microCT) was used to generate threedimensional images to visualize the internal structure of the material before and after the tests, and to quantitatively assess the evolution of pore structures and cracking by a computational routine developed. First, the FIJI software was used to reduce noises of images, then the images generated before and after the tests was aligned using the DataViewer software. In the Dragonfly software the voids (pores and fissures) of the images are segmented and quantified, showing the volume and sphericity of the voids of interest.The results of the cyclic load test showed that when the specimen was submitted to 30 per cent of its ultimate strength almost no influence in the internal structure was observed.When the cyclic load was increased to 50 per cent and 70 per cent significant damage to the specimens was noticed. The results of the qualitative and quantitative analysis of the specimen submitted to 100 Celsius degrees and 200 Celsius degrees showed the appearance of small cracks, however, the pore structures did not change. In the specimen subjected to 450 Celsius degrees the appearance of several cracks was visualized. For the sample submitted to 650 Celsius degrees specimen was imposed to the material, making it impossible to visualize in the microCT. As a conclusion, the Class G Oil Well Cement Paste may be used for operations with cyclic loading up to 30 per cent of the ultimate strength with service temperatures up to 200 Celsius degrees. Finally, the dehydroxylation of Ca(OH)2 and degradation of CaCO3 led to high deterioration in this cement paste.

Este trabalho consiste em um estudo do comportamento de nós de pórtico de ligações viga-pilar de concreto armado submetidos a ações cíclicas. O trabalho é composto por duas etapas: uma de investigação experimental e outra de cunho teórico. A etapa experimental teve como base os ensaios realizados em cinco modelos físicos de ligações viga-pilar. Os resultados desses ensaios permitiram a observação de diversos aspectos do comportamento estrutural dos nós de pórtico frente às ações cíclicas e a avaliação da influência de algumas variáveis. Neste trabalho, as variáveis escolhidas foram a variação do carregamento aplicado e o detalhamento da armadura transversal na região do nó. Os principais efeitos das ações cíclicas sobre as cinco ligações ensaiadas foram: aumento generalizado dos deslocamentos globais, perda de resistência e de rigidez dos elementos estruturais, propagação e aumento da abertura das fissuras inicialmente formadas, tendência de uniformização das deformações dos estribos do nó ao longo dos ciclos e maior deterioração do nó de pórtico em relação aos elementos viga e pilar. Na etapa teórica, foram empregados essencialmente dois tipos de modelos: i) modelos derivados das idealizações dos modelos clássicos de biela e tirante. ii) modelos simplificados que empregam conceitos da Mecânica do Dano e da Fratura, para a avaliação dos efeitos de perda de rigidez (dano) e das deformações permanentes (plasticidade) na resposta global da ligação viga-pilar. Por fim, foram feitas comparações entre os resultados experimentais e teóricos, chegando-se a importantes conclusões sobre o comportamento mecânico do nó frente às cargas cíclicas e sobre a eficiência dos modelos teóricos em simular a resposta do nó de pórtico e da ligação como um todo. As comparações mostraram que, dentro de certos limites, os modelos teóricos fornecem resultados satisfatórios frente aos resultados experimentais / The present thesis studies the behavior of frame joints in reinforced concrete beam-column joints subjected to cyclic loads. The thesis is divided into two parts: an experimental study and a theoretical-based study. The experimental study is based on laboratory tests on five physical models of beam-column joints. The results of this experimental study permitted the observation of various aspects of the structural behavior of frame joint subjected to cyclic load and estimating the influence of certain variables the affect the behavior of such joints. In the present thesis, the variables studied are the applied load and reinforcement detailing at the joint location. The effects of cyclic loads on the tested joints were: an increase in the overall deformation, loss of strength and stiffness of structural elements, crack propagation and increase in crack width of previously formed cracks, a tendency towards a uniform strain distribution in the transverse reinforcement at the joint section and a more rapid deterioration of frame joints compared to beam/column joints. At the theoretical level, two types of models were used to study the behavior of the joint: i) a model derived from the idealization of the classical strut-tie model, and ii) a simplified damage and fracture mechanics-based model for estimating the effects of the loss of stiffness (damage) and permanent strains (plasticity) on the overall response of the beam column joint. To reach any conclusion on the mechanical behavior and the efficiency of existing theoretical models employed in the design of reinforced beam-column joints and other joints subjected to cyclic loading, a comparative study between the theoretical and experimental results was carried out. The results show that within certain limits, the theoretical models employed are in good agreement with experimental results

[pt] Os efeitos catastróficos de terremotos que frequentemente acontecem na costa ocidental da América do Sul motivaram a realização desta pesquisa. O Equador, em particular, encontra-se localizado em uma zona de alta atividade sísmica devido a processos de subducção de placas tectônicas que originam sismos de grande magnitude, como o terremoto de magnitude Mw igual 7.8 acontecido em 16 de abril de 2016 na cidade costeira de Pedernales, que produziu grandes danos à infraestrutura e perdas de vidas humanas. A presente pesquisa tem como objetivo estudar o comportamento dinâmico de dois tipos de estruturas de terra: um talude de encosta composto de solo coluvial de altura aproximada de 70 m e a barragem de enrocamento de Mazar construída com altura de 166 m para fins de aproveitamento hidrelétrico. A barragem de Mazar, em função da sua altura, é classificada como barragem de grande tamanho pela International Commission on Large Dams (ICOLD) e qualificada pela Norma Equatoriana da Construção (NEC, 2014) como estrutura de importância essencial, com obrigatoriedade de verificação do seu desempenho sísmico para dois terremotos de projeto: o terremoto operacional base (OBE) e o máximo terremoto provável (MCE) com períodos de retorno de 475 anos e 2500 anos, respectivamente. As análises efetuadas neste trabalho incluíram a geração de sismos de projeto, investigação da estabilidade estática e pseudoestática de taludes, determinação de deslocamentos permanentes mediante métodos analíticos simplificados e simulações numéricas. Diferenças significativas nos deslocamentos permanentes máximos foram observadas empregando as abordagens analítica e numérica. / [en] The catastrophic effects of earthquakes that frequently occur on the West coast of South America motivated this research. Ecuador, in particular, is located in a zone of high seismic activity due to processes of tectonic plate subduction that give rise to earthquakes of great magnitude, such as the seismic motion of magnitude Mw equal 7.8 that struck the coastal city of Pedernales on April 16 2016, producing great damages to the infrastructure and losses of human lives. The present research aims to study the dynamic behavior of two types of earth structures: a slope composed of colluvial soil of approximately 70 m height and the Mazar rockfill dam constructed for hydroelectric generation. The Mazar dam, according to its height (166 m), is classified as a large dam by the International Commission on Large Dams (ICOLD) and qualified by the Ecuadorian Construction Standard (NEC, 2014) as a structure of essential importance, with mandatory analysis of seismic performance under two seismic design ground motions: the operating basis earthquake (OBE) and the maximum credible earthquake (MCE) with return periods of 475 years and 2500 years, respectively. The analyses carried out in this work included the generation of the OBE and MCE earthquakes, investigation of static and pseudo static stability of slopes, determination of permanent displacements using simplified analytical methods and numerical simulations. Significant differences in the maximum permanent displacements were observed using analytical and numerical approaches.

[pt] O concreto de ultra-alto desempenho (CUAD) é um material cimentício avançado que possui excelente desempenho mecânico, ductilidade e durabilidade devido a uma elevada densidade de empacotamento e ao uso de fibras, promovendo benefícios à vida útil das estruturas. Grande parte das estruturas está sujeita a ações cíclicas, ou seja, variáveis com o tempo, resultando em danos de fadiga, como o surgimento e a propagação de trincas, que podem comprometer sua integridade. Assim, é essencial compreender o comportamento dos materiais sob fadiga para que sejam propostas diretrizes de projeto seguras e adequadas ao bom funcionamento das estruturas. Este trabalho visa, portanto, investigar o comportamento do concreto de ultra-alto desempenho pré-fissurado sob fadiga na flexão, quantificando sua degradação mecânica ao longo do carregamento cíclico a partir dos parâmetros de abertura de fissura (CMOD) e rigidez, contribuindo para o estudo desse tipo especial de concreto. Foram propostas equações para prever a vida à fadiga em relação ao limite superior de carga e estabelecer o limite de fadiga do concreto de ultra-alto desempenho, igual a 75,3 por cento, considerando o limite inferior igual a 30 cento do limite superior. Ainda, avaliou-se o comportamento pós-fadiga de amostras que não sofreram ruptura ao longo de 1.000.000 de ciclos, sendo possível observar que o mecanismo não gerou alterações no desempenho das amostras sob flexão para limites inferiores ao limite de fadiga. / [en] Ultra-high Performance Concrete (UHPC) is an advanced cementitious material that has excellent mechanical performance, ductility and durability due to a high packing density and the use of fibers, contributing to increase the structures lifespan. Most of the structures are subject to cyclic loads, which vary with time, resulting in fatigue damage such as the formation and propagation of cracks that could compromise its integrity. Thus, it is essential to understand the behavior of materials subjected to fatigue so that safe and proper design guidelines can be proposed for the appropriate performance of the structures. Therefore, this work aims to investigate the behavior of pre-cracked ultra-high performance concrete under flexural fatigue, quantifying its mechanical deterioration during cyclic loading through both crack mouth opening displacement (CMOD) and stiffness, which will contribute to the study of this special type of concrete. Equations were proposed to predict fatigue life according to the upper load limit during the cyclic loading and to establish the endurance limit of ultra-high performance concrete in 75,3 percent, considering the lower limit load equal to 30 percent of the upper limit. Also, when evaluating the post-fatigue behavior of samples that did not fail over 1,000,000 cycles it was possible to identify that the cyclic loading did not change the performance of the samples under bending, which was due to the use of upper loads below the endurance limit.

Improvements in quality of life, population growth, and environmental restrictions associated with the burning of fossil fuels will accentuate the need for renewable energy and energy geo-storage. A salient characteristic of these systems is that they impose numerous cycles of effective stress, temperature, and humidity on the surrounding geomaterials. This thesis quantifies future energy consumption based on realizable scenarios and explores the behavior of geomaterials subjected to mechanical and thermal cycles in view of energy-related applications. The long-term behavior of geotechnical systems subjected to a large number of mechanical load cycles is studied with a new numerical scheme based on a hybrid finite element formulation. The numerical scheme satisfies initial conditions as well as fundamental characteristics of soil behavior, such as threshold strain, terminal density, and long-term ratcheting. Numerical results show that shallow foundations subjected to repetitive loading experience strain accumulation and stress redistribution. On the other hand, the long-term behavior of energy piles, exposed geomembranes on slopes, and jointed rock masses subjected to cyclic thermal changes is studied using a combination of numerical, analytical, and experimental methods. Results show that thermal cycles lead to the gradual accumulation of plastic displacements, which may be amplified by thermally-induced wedging in jointed rock masses. In general, cumulative effects caused by repetitive loads increase with the number of cycles, the static factor of safety, the amplitude of the cyclic excitation, and the magnitude of the cyclically-induced displacement with respect to the critical elastic displacement.

Ageing infrastructure that is shear deficient and may be at risk of brittle collapse, particularly in seismically active regions, can be economically strengthened using externally bonded fibre-reinforced polymers (FRP). Although many studies have been conducted on small-scale specimens subject to monotonic loading, little experimental data exists for large-scale specimens and those tested under reversed cyclic loading to simulate a seismic event. An experimental study of large-scale (400 mm x 650 mm) beam specimens strengthened in shear with FRP was conducted to examine the effects of reversed cyclic loading and to quantify material shear strength contributions. Testing showed that FRP retrofits were highly effective at improving shear performance and were not adversely affected by reversed cyclic loading prior to the occurrence of flexural yielding. The shear resistance attributed to concrete was found to remain relatively consistent with reversed cyclic loading prior to flexural yielding, after which point concrete strength decay was apparent. The loss of concrete shear resistance directly influenced the rate of FRP straining and the achievable ductility. An analytical model using the Modified Compression Field Theory (MCFT) was developed for externally bonded FRP reinforcement to describe the experimental behaviour and to evaluate the accuracy of current FRP design methods. Failures were accurately modelled when appropriate FRP strain limits were used for the ultimate strength and for the stress transfer capacity across the shear crack. Proposed FRP strain limits were developed considering the strain distribution along the crack plane. In addition, improved strain limits incorporate the effect of rupture failure due to stress concentrations in the FRP wrapped around the beam corners. The proposed FRP formulations offer improved accuracy over the current FRP design methods (CSA S6-06 and ACI 440.2R-08), which suggest a broadly applied maximum strain limit of 0.004 mm/mm, which was determined to be overly conservative for FRP rupture failures.