Einleitung: Aufgrund der hohen Inzidenz der vorderen Kreuzbandverletzungen und der damit einhergehenden funktionellen Einschränkung besteht ein anhaltendes Interesse an der Verbesserung bestehender und Entwicklung neuer, besserer Techniken zur Rekonstruktion dieser Bandstruktur des Kniegelenkes. In dieser Studie wurde der Einfluss des Verankerungsniveaus (anatomisch vs. extrakortikal) und der Verankerungsart (direkt vs. indirekt) auf das mechanische Verhalten von drei exemplarischen, in der Klinik häufig angewandten Rekonstruktionstechniken, untersucht. Material & Methoden: An insgesamt 24 Kniegelenken humaner Spender mittleren Alters (40 Jahre) wurden drei Rekonstruktionstechniken (n=8 pro Gruppe) des VKB durchgeführt. Als Transplantat wurden jeweils humane Hamstringsehnen verwendet: 1.) HADBIO: anatomische und direkte Verankerung mit biodegradierbaren Interferenzschrauben, 2.) HADTIT: semi-anatomische und direkte Verankerung mit Titanschrauben, 3.) HEIButton: extrakortikale, indirekte Verankerung mit Faden-Button Verbindung. Alle rekonstruierten Kniegelenke wurden einer zyklischen, inkremental zunehmenden Belastung bis zum Versagen unterzogen. Es wurden die Parameter Konstruktsteifigkeit, absorbierte Energie, Transplantatauslenkung und Laxizitätszunahme bei Belastungen von 200, 300, 400 N, sowie die maximale Steifigkeit und Versagenskraft bestimmt. Ergebnis: Die anatomische und direkte Transplantatverankerung mit biodegradierbarer Interferenzschraube zeigt die vorteilhaftesten mechanischen Eigenschaften, während die extrakortikale und indirekte Verankerung die niedrigsten mechanischen Eigenschaften aufwies. Die tibiale Verankerungsseite ist bei Interferenzschraubenverankerung der Schwachpunkt, während die Fadenverbindungen bei der extrakortikalen Verankerungstechnik die Schwachstelle darstellten. Auch bei anatomischer und direkter Transplantatfixation findet ein nicht zu vernachlässigender permanenter Verankerungsverlust bei vergleichsweise geringer Versagenskraft statt, der vor allem auf der tibialen Verankerungsseite zu beobachten ist. Diskussion: Eine anatomische und direkte Transplantatverankerung ist von mechanischem Vorteil. Allerdings hängt die Konstruktsteifigkeit auch in erheblichem Maße vom Fixationsobjekt ab. Extrakortikale Fixationstechniken, die eine indirekte Faden-Knoten-Transplantatverbindung erfordern, unterliegen einer erheblichen nicht-reversiblen Lockerung unter zyklischer Belastung und sollten durch direkte Verankerungstechniken ersetzt werden. Aufgrund der permanenten Laxizitätszunahme auch in der anatomischen und direkten Interferenzschraubenverankerung, vor allem der tibialen Seite, sollte über Sicherungsverankerungen, so genannten Hybridfixationen nachgedacht werden, um die mechanischen Vorteile dieser Rekonstruktionsart voll zum Tragen bringen zu können. / Introduction: There is a continuous interest in the improvement and development of new techniques for the reconstruction of the anterior cruciate ligament (ACL) because of the high incidence of its injury and the resulting functional deficit. Purpose of this study was the impact of fixation level (anatomic vs. extracortical) and fixation method (direct vs. indirect) on the mechanical properties of three frequently used reconstruction techniques. Material & Methods: 24 human cadaveric knees with an average age of 40 years were used for simulation of three reconstruction techniques (n=8 per group). Human hamstring tendons were utilized as tendon grafts. 1.) HADBIO: anatomic and direct fixation with biodegradable interference screws, 2.) HADTIT: semi-anatomic and direct fixation with titanium interference screws, 3.) HEIButton: extracortical, indirect fixation with tape/button combination. All reconstructed knee joints underwent cyclic incremental loading until failure. Construct stiffness, absorbed energy, displacement and laxity increase were calculated at loads up to 200, 300, 400 N. Maximum stiffness and failure load were also recorded. Results: The anatomic and direct graft fixation with biodegradable interference screws provided the highest, while the combination of extracortical and indirect fixation showed the lowest mechanical properties. The tibial fixation site is the critical factor in interference screw fixation, while the tape/suture interfaces were the location of failure in the extracortical reconstructions. Even in the anatomic and direct reconstruction technique a considerable permanent loss of fixation, especially at the tibial fixation site and a comparably lower failure load were observed. Discussion: The combination of anatomic and direct fixation showed to be of mechanical benefit. However, construct stiffness seemed to be also affected by the fixation device. Extracortical fixation techniques, which require suture-tape/knot interfaces for graft fixation, undergo significant permanent loosening of fixation under cyclic loads and should be replaced by direct fixation techniques. Since a permanent laxity increase was still observed in the anatomic and direct interference screw reconstructions, especially on the tibial site, backup or so called hybrid fixations should be considered, which would allow to take full advantage of the mechanical improvements in these reconstruction techniques.

Le but de cette étude est d'étudier le renforcement des sols par inclusions rigides sous chargement complexe et cyclique. L'effet de certains paramètres liés à la définition d’un chargement complexe et cyclique sur le comportement du système est mis en évidence.Du point de vue des chargements statiques complexes, des semelles de fondation posées sur un sol compressible renforcé par inclusions rigides sans matelas soumis à des charges centrées, excentrées verticales et horizontales et à quelques cycles de charge ont été étudiées. Des approches numériques et expérimentales sont présentées. Les résultats des mesures expérimentales et numériques permettent de mettre en évidence le comportement de ces systèmes en termes de contrainte sur la tête d'inclusion et sur le sol compressible, de déplacements verticaux et latéraux de la semelle et du déplacement latéral de l'inclusion. L'efficacité de la semelle renforcée est comparée à celle d’une semelle non renforcée.Une modélisation 3D de solutions de fondations pour les éoliennes est étudiée. La combinaison d’un chargement vertical et de différents moments appliqués à la fondation est prise en compte. Le sol compressible renforcé par inclusions rigides est considéré comme une option qui est comparée à d’autres solutions plus classiques (fondation superficielle et radier sur pieux). Les résultats obtenus permettent de présenter l’impact sur le tassement du sol, la rotation de la fondation, les efforts axiaux et les moments fléchissants dans les inclusions rigides. Les résultats numériques indiquent enfin que la technique d'amélioration du sol par inclusions rigides peut être une solution appropriée pour les fondations d'éoliennes.En ce qui concerne les aspects cycliques, trois points principaux sont abordés. Dans un premier temps, la modélisation numérique d’essais en laboratoire d’un renforcement de sol par inclusions rigides soumis à des chargements monotones et des cycles limités de chargement mise en œuvre. Le modèle hypoplastique (HYP) est utilisé pour modéliser le comportement de la plate-forme de transfert de charge. Les résultats numériques sont validés à la fois par rapport aux données expérimentales et numériques de Houda (2016). L'influence des conditions aux limites et de l'état du sol compressible est mise en évidence. Les résultats numériques indiquent qu'il est possible de considérer le comportement cyclique du sol renforcé par inclusions rigides en utilisant le modèle HYP.Dans un second temps, un remblai renforcé par des inclusions rigides sous un nombre élevé de chargement cyclique est étudié. Deux niveaux de complexité différents pour le modèle constitutif (HYP et le modèle élastique linéaire parfaitement plastique avec un critère de rupture de type Mohr-Coulomb) ont été pris en compte pour étudier le comportement de la LTP et analyser le comportement cyclique du système. Le modèle HYP est proposé pour la suite des études car il permet de bien capturer la décroissance et l’accumulation des tassements avec le nombre de cycles de charge. L'effet des paramètres qui sont le nombre de cycles de charge, l'amplitude et la fréquence (induite par la vitesse du trafic) et la hauteur du remblai est également présentée.Finalement, une étude sur la réponse cyclique d'un remblai de GRPS est menée. En comparant le remblai renforcé par des géosynthétiques (GRPS) avec le remblai renforcé par inclusions (PE), le rôle du géosynthétique est mis en évidence sous des chargements statiques et cycliques. L'influence du nombre de cycles de chargement et du nombre de géosynthétiques sur l'effet de voute et les tassements cumulés est également discutée. / The aim of the study is to investigate the soil improvement by rigid inclusions under complex and cyclic loadings, and to highlight the effect of some parameters related to complex and cyclic loading on the system behavior.Concerning the static complex loading, footings over rigid inclusion-reinforced soil without mattress subjected to centered, eccentrically vertical and horizontal loads, and load cycles are first studied. Numerical and experimental approaches are presented. Monitored and numerical results permit to show the behavior of these reinforced systems in terms of stresses on the inclusion head and soft soil, vertical and lateral displacements of the footings and lateral displacement of the inclusions. The efficiency of the reinforced footing is also presented and compared to the unreinforced one.A 3D modeling of the foundation solutions for wind turbines is presented. The combination of vertical loading and different moments applied to the foundation is taken into account. The inclusion-improved soft soil under footing is considered as a foundation option and, compared to classical ones (shallow foundation and piled raft). The obtained results are illustrated concerning the ground surface settlements, the foundation rotations, the axial forces and bending moments of the reinforcements. The numerical results indicate that the soil improvement technique by rigid inclusions can be an appropriate solution for the wind turbine foundations.With regard to the cyclic aspects, three main concerns are studied. Firstly, the numerical modeling of laboratory tests on a soil improvement by rigid inclusions subjected to monotonic loading and a limited load cycles is carried out, in which the hypoplasticity (HYP) model is used to model the load transfer platform (LTP). The numerical results are validated against both the experimental data and numerical ones of Houda (2016). The influence of the boundary condition and soft soil state are figured out. The numerical results indicate that it is possible to address the cyclic behavior of the rigid inclusion-reinforced soil by using the HYP model.Secondly, a piled embankment under a high number of cyclic loadings is studied. Two different levels of complexity for the constitutive models are used (HYP and a simpler one the linear elastic perfectly plastic constitutive model with a shear criteria of Mohr-Coulomb). These models were considered to model the behavior of the LTP and analyze the cyclic behavior of the system. The HYP model is then suggested for the following studies since it can capture well the arching decrease and the cumulated settlements under the load cycles number. The effect of the parameters that are load cycles number, amplitude and frequency (induced by traffic speed), and embankment height is illustrated as well.Finally, a study on the cyclic response of a GRPS embankment is conducted. By comparing the geosynthetic-reinforced pile-supported (GRPS) embankment with the piled embankment (PE), the role of the geosynthetic is verified under static and cyclic loading aspects. The influence of the load cycles number and the geosynthetic layers number on the arching effect and cumulative settlements is shown as well.

Trabecular bone is a porous composite material which consists of a mineral phase (mainly hydroxyapatite), organic phase (mostly type I collagen) and water assembled into a complex, hierarchical structure. In biomechanical modelling, its mechanical response to loads is generally assumed to be instantaneous, i.e. it is treated as a time-independent material. It is, however, recognised that the response of trabecular bone to loads is time-dependent. Study of this time-dependent behaviour is important in several contexts such as: to understand energy dissipation ability of bone; to understand the age-related non-traumatic fractures; to predict implant loosening due to cyclic loading; to understand progressive vertebral deformity; and for pre-clinical evaluation of total joint replacement. To investigate time-dependent behaviour, bovine trabecular bone samples were subjected to compressive loading, creep, unloading and recovery at multiple load levels (corresponding to apparent strain of 2,000-25,000 με). The results show that: the time-dependent behaviour of trabecular bone comprises of both recoverable and irrecoverable strains; the strain response is nonlinearly related to applied load levels; and the response is associated with bone volume fraction. It was found that bone with low porosity demonstrates elastic stiffening followed by elastic softening, while elastic softening is demonstrated by porous bone at relatively low loads. Linear, nonlinear viscoelastic and nonlinear viscoelastic-viscoplastic constitutive models were developed to predict trabecular bone's time-dependent behaviour. Nonlinear viscoelastic constitutive model was found to predict the recovery behaviour well, while nonlinear viscoelastic-viscoplastic model predicts the full creep-recovery behaviour reasonably well. Depending on the requirements all these models can be used to incorporate time-dependent behaviour in finite element models. To evaluate the contribution of the key constituents of trabecular bone and its microstructure, tests were conducted on demineralised and deproteinised samples. Reversed cyclic loading experiments (tension to compression) were conducted on demineralised trabecular bone samples. It was found that demineralised bone exhibits asymmetric mechanical response - elastic stiffening in tension and softening in compression. This tension to compression transition was found to be smooth. Tensile multiple-load-creep-unload-recovery experiments on demineralised trabecular samples show irrecoverable strain (or residual strain) even at the low stress levels. Demineralised trabecular bone samples demonstrate elastic stiffening with increasing load levels in tension, and their time-dependent behaviour is nonlinear with respect to applied loads . Nonlinear viscoelastic constitutive model was developed which can predict its recovery behaviour well. Experiments on deproteinised samples showed that their modulus and strength are reasonably well related to bone volume fraction. The study considers an application of time-dependent behaviour of trabecular bone. Time-dependent properties are assigned to trabecular bone in a bone-screw system, in which the screw is subjected to cyclic loading. It is found that separation between bone and the screw at the interface can increase with increasing number of cycles which can accentuate loosening. The relative larger deformation occurs when this system to be loaded at the higher loading frequency. The deformation at the bone-screw interface is related to trabecular bone's bone volume fraction; screws in a more porous bone are at a higher risk of loosening.

Carregamentos cíclicos são causados de diversas maneiras, como tráfego de veículos, ondas, vento e terremotos. Nos últimos anos, particularmente, tem-se aumentado o número de estudos para este tipo de carregamento devido ao desenvolvimento da engenharia offshore. Além disso, técnicas de melhoramento de solos granulares têm sido empregadas para alterar as características dos solos naturais, com o objetivo de aumentar sua resistência e retardar - ou evitar - a ocorrência de liquefação. Alguns estudos anteriores desenvolveram leis constitutivas completas para areias reforçadas com fibras sob carregamento monotônico, mas não são encontrados na literatura trabalhos sobre a modelagem deste tipo de solos sob carregamentos cíclicos. Sendo assim, essa dissertação desenvolve e valida um novo modelo constitutivo capaz de avaliar o comportamento de solos granulares reforçados com fibras sob carregamento cíclico sob condições não-drenadas. Este modelo é baseado em dois modelos previamente desenvolvidos por Diambra et al. (2013) e Diambra e Ibraim (2014), que utilizam uma técnica de homogeneização para considerar a contribuição da areia e das fibras. O comportamento da areia segue o Modelo Severn-Trent Sand, proposto por Gajo e Muir Wood (1999). Uma vez estruturado o modelo e definido seu procedimento de cálculo, realiza-se uma análise paramétrica, a fim de demonstrar a influência de cada parâmetro das fibras e da areia no comportamento do compósito. Um fator de ajuste para levar em consideração a mudança nas forças interparticulares causada pelas fibras é proposto neste trabalho. Ao final, o modelo é calibrado com resultados experimentais e faz-se uma análise de suas competências e limitações. O processo de calibração mostrou que o modelo é capaz de capturar importantes tendências causadas pela inserção de fibras, como a redução nas deformações axiais e na geração de poropressões, retardando a ocorrência de liquefação. O modelo proposto mostrou-se mais efetivo em reproduzir o comportamento de areias fofas, ou seja, aquelas cujo estado de tensões se encontra acima da linha do estado crítico. / Cyclic loads are induced by several sources, such as traffic, waves, wind and earthquakes. Particularly in the last years, more attention has been given to such loading conditions due to the development of the offshore engineering. Additionally, ground improving techniques have been employed to alter the characteristics of natural soils in order to increase its strength and delay – or avoid – liquefaction. Previous studies have developed complete constitutive laws for fibre-reinforced sands under monotonic loading conditions, but no previous work on modelling granular soils under cyclic loading has been reported. Hence, this research develops and validates a new constitutive modelling which is capable to fully assess the behaviour of fibre-reinforced soils under cyclic loads for undrained conditions. This model is based on two previous models developed by Diambra et al. (2013) and Diambra and Ibraim (2014), which employed a homogenisation technique to scale sand and fibre contribution. The behaviour of the sand follows the Severn-Trent Sand Model proposed by Gajo and Muir Wood (1999). Once the model is structured and its calculation procedure is defined, a parametric analysis is carried out in order to show the influence of each fibre and sand parameter in the composite response. An adjustment factor to account for the change in the interparticle forces caused by the fibres is proposed. Finally, the model is calibrated with experimental results and an analysis of its competences and limitations is performed. The calibration process showed that the model is able to capture important trends caused by the fibre reinforcement, such as a reduction in axial strain and in pore pressure generation, delaying the occurrence of liquefaction. The proposed model was shown to be more effective in reproducing the response of loose sands, i.e. those whose stress states are above the critical state line.

O presente trabalho teve como objetivo desenvolver uma metodologia prática e confiável para previsão de vida à fadiga de juntas soldadas a cordão pelo processo MIG/MAG, quando estas estão submetidas a carregamentos cíclicos combinados. A máxima tensão linear no pé da solda, região típica de início de trinca, conhecida como hot spot foi utilizada para prever a vida através do método de Fadiga de Alto Ciclo S x N (Tensão x Vida), largamente empregado em códigos de projeto de estruturas soldadas. O Método dos Elementos Finitos foi utilizado para determinação das tensões estruturais resultantes do carregamento e das descontinuidades geométricas presentes nos cordões de solda. A análise de fadiga foi efetuada em ambiente virtual, através de um software (programa) de fadiga capaz de importar as tensões atuantes na região da solda para cada carregamento, combinando-as e obtendo assim a vida à fadiga decorrente da somatória dos diferentes tipos de carregamento ao qual a junta foi submetida. As propriedades monotônicas e cíclicas dos materiais da junta foram obtidas da literatura e de um extenso banco de dados disponível no software de fadiga. Estas propriedades foram ajustadas com base em ensaios de laboratório nas juntas investigadas. A medição ou modelagem das tensões residuais inerentes ao processo de soldagem não fazem parte do escopo deste trabalho. Contudo, os efeitos térmicos e metalúrgicos resultantes do processo de soldagem, como distorções, tensões residuais, variações microestruturais e propriedades mecânicas foram considerados de forma indireta, através da correção das curvas de fadiga nos corpos de prova investigados. Corpos de prova do tipo tubo-placa foram submetidos a carregamentos cíclicos combinados (flexão e torção) de amplitude constante. O resultado da análise virtual de durabilidade foi, portanto, calibrado com base nestes experimentos e curvas disponíveis em códigos de projeto de fadiga como BS7608 e Eurocode 3. A aplicabilidade deste método numérico-experimental e suas contribuições para a garantia da Integridade Estrutural do projeto de juntas soldadas são apresentadas. Seus desafios e melhorias são por fim discutidos. / The main purpose of this work is to develop a practical and robust methodology to evaluate the fatigue life in seam weld joints fabricated with GMAW process when subjected to combine cyclic loading. The maximum linear stress at the typical crack initiation region, better known as hot spot stress, was used to calculate the fatigue life through high cycle fatigue method S x N (Stress x Life), widely used in design codes for the life assessment of welded structures. The Finite Element Method (FEM) was used to obtain the structural stresses distribution due the external loading and geometric discontinuities very common in seam weld joints. The fatigue analysis was conducted in virtual environment. The FEM stress results from each loading were imported to fatigue code FE-Fatigue and combined to perform the fatigue life prediction. The monotonic and cyclic properties of the joint materials were obtained in the literature and from the fatigue software database. These properties were adjusted based on laboratory fatigue tests in the investigated welded joints configurations. The measurement or modeling of the residual stresses resulted from the welded process is not part of this work. However, the thermal and metallurgical effects, like distortions and residual stresses, were considered indirectly through fatigue curves corrections in the samples investigated. A tube-plate specimen was submitted to combine cyclic loading (bending and torsion) with constant amplitude. The virtual durability analysis result was calibrated based on these laboratory tests and design codes such as BS7608 and Eurocode 3. The feasibility and application of the proposed numerical-experimental methodology and contributions for the welded joints structural integrity design are presented. The challenges and improvements are finally discussed.

Onshore wind turbine foundations are mainly subjected to large overturning moments. The wind action imposes cyclic and dynamic loading conditions which occur in extreme and service scenarios. Deep foundations, when used, transfer this large overturning moment through a pile group which combines the axial and lateral resistance of all piles. Several authors noticed that cyclic axially loaded piles could have their resistance reduced due to shaft friction degradation. Considerable efforts have been made to understand this degradation phenomenon. However, the design and performance of cyclic axial loaded piles require greater advances. Therefore, this research sought to assess the shaft friction degradation of axially loaded piles in wind turbine deep foundations, especially for those located in Brazil. Several issues related to the main objective of this study had to be addressed because onshore wind turbine foundations are an area of recent research, especially in Brazil. The first stage of this research explored the key aspects of onshore wind turbine foundations in Brazil and compared them with the worldwide status. The main reason to explore this subject is that several authors consider onshore wind turbine foundations a well-understood topic; however, limited data from actual situations have been published, especially in developing countries where wind energy projects have recently started. Thus, a survey on Brazilian energy companies and foundation designers was conducted, and the first Brazilian database of wind turbine foundations was created. This database contains data from more than three thousand Brazilian wind turbine foundations. The key aspects, types and dimensions of these foundations were summarized. Worldwide, concrete gravity foundations are the most commonly used foundation type for onshore wind turbines. In Brazil, 43.3% of the wind turbines had shallow foundations, essentially concrete gravity, and 56.7% had deep foundations, mostly continuous flight auger piles. The foundation type was chosen according to the local foundation expertise and geotechnical conditions, which included soil type, water table level, soil layer resistance, the extent of porous soil layers and bedrock depth. This first stage of the research identified that Brazilian wind turbine foundations are significantly different from other countries. Approximately 70% of Brazilian wind turbine deep foundations used continuous flight auger piles, most of them embedded in sandy soils. Therefore, experimental investigations of the sand-concrete interface response under monotonic and cyclic loading are essential. The second and third stages of this research sought to investigate the sand-concrete interface response based on this recent insight. The second stage assessed the sand-concrete interface response through monotonic interface direct shear tests under different confinement conditions. The role of surface structural characteristics, confinement condition, sand mean diameter, particle morphology, sand gradation and relative density were evaluated. A nonlinear conceptual model of the interfacial-to-internal friction angle ratio was proposed according to normalized roughness and normalized waviness. Additionally, multiple regression was used to estimate the sand-concrete interface strength by the effect of constant normal stiffness. The results were essential to understand and to predict the sand-concrete interface response of concrete piles under static axial loading. The third stage explored the shaft friction degradation of cyclic axial loaded piles through sand-concrete and sand-steel cyclic interface direct shear tests. In geotechnical engineering practice, field and experimental tests are usually performed to evaluate the number of cycles until failure occurs under constant cyclic amplitude. According to this approach, cyclic failure can either occur quickly or not at all. From a practical viewpoint, the cyclic test times are unpredictable, which makes these tests difficult to plan and to perform. Therefore, a new approach based on increasing cyclic amplitude is proposed to overcome the conventional method. A simple cumulative damage model established a relationship between the cyclic loaded tests under constant and increasing cyclic amplitudes. The new approach provides additional insights into the cyclic interfacial response, such as the effect of previous cycles, the cyclic amplitude at failure and the displacement development throughout cycling. This new approach can be effortlessly extended to other experimental and field investigations. From a practical viewpoint, this new approach can reduce the cost and duration of projects. The author believes that this dissertation brought breakthroughs to the wind energy companies and to the geotechnical engineering community. However, further studies on onshore wind turbine foundations are still required. / As fundações de torres eólicas onshore são submetidas a grandes momentos de tombamento. A ação do vento impõe carregamentos cíclicos e dinâmicos que ocorrem em condições operacionais e extremas. Fundações profundas, quando usadas, transferem esse momento de tombamento através de um grupo de estacas que, por sua vez, são submetidas a esforços axiais e laterais. Muitos estudos observaram que estacas submetidas ao carregamento cíclico axial estão sujeitas à degradação do atrito lateral. A fim de compreender essa degradação, diversas pesquisas foram realizadas. No entanto, o dimensionamento e desempenho de estacas submetidas ao carregamento cíclico axial requer maiores avanços. Dessa forma, esta pesquisa buscou avaliar a degradação do atrito lateral em estacas de torres eólicas, principalmente aquelas localizadas no Brasil. Da mesma forma, foram abordados assuntos relacionados ao objetivo principal deste estudo uma vez que pesquisas sobre fundações de torres eólicas onshore ainda são incipientes, especialmente no Brasil. A primeira etapa da pesquisa explorou as principais características das fundações de torres eólicas onshore no Brasil e comparou-as com a prática internacional. Investigou-se este assunto uma vez que diversos autores consideram as fundações de torres eólicas onshore um tópico já compreendido; entretanto, a quantidade de informações e dados publicados são ínfimos, especialmente em países em desenvolvimento onde os projetos eólicos iniciaram recentemente. Por essa razão, realizou-se uma pesquisa com as empresas e projetistas do setor a fim de criar o primeiro banco de dados brasileiro sobre fundações de torres eólicas onshore. Esse banco de dados possui mais de três mil fundações cadastradas. Os principais aspectos, tipos e dimensões dessas fundações foram apresentados. Internacionalmente, o tipo de fundação mais empregado para torres eólicas onshore são fundações superficiais de gravidade. No Brasil, 43.3% das torres eólicas apresentam fundações superficiais, essencialmente fundações de gravidade, e 56.7% das torres eólicas apresentam fundações profundas, principalmente por grupo de estacas hélice continua. O tipo da fundação foi determinado com base na expertise local e condições geotécnicas, incluindo o tipo de solo, nível de água, resistência do solo, espessura de camadas porosas e profundidade do topo rochoso. Identificou-se, através da primeira etapa, que as fundações de torres eólicas onshore no Brasil são significantemente diferentes de outros países. Aproximadamente 70% das fundações profundas são por grupo de estacas hélice contínua, sendo na maior parte em contato com solos arenosos. Desta forma, há necessidade de realizar investigações experimentais da interface areia-concreto. A segunda e terceira etapas desta pesquisa concentraram-se no comportamento estático e cíclico da interface areia-concreto. A segunda etapa avaliou o comportamento estático da interface areia-concreto através de ensaios de cisalhamento direto em diferentes condições de confinamento. Foram avaliadas as influências das características da superfície sólida, diâmetro médio dos grãos, morfologia dos grãos, distribuição granulométrica e densidade relativa. Um modelo não linear do ângulo de atrito na interface de acordo com a rugosidade e ondulação normalizadas foi proposto. Além disso, empregou-se uma regressão múltipla para estimar a resistência da interface areia-concreto de acordo com a constante de rigidez. Os resultados foram essenciais na compreensão e previsão do comportamento estático da interface de estacas de concreto. A terceira etapa explorou a degradação do atrito lateral em estacas através de ensaios de cisalhamento direto cíclicos na interface areia-concreto e areia-aço. Usualmente, campanhas experimentais são conduzidas para avaliar o número de ciclos até ruptura com uma amplitude cíclica constante. A ruptura geotécnica pode ocorrer rapidamente ou nunca ocorrer; e, desta maneira, a duração dos ensaios é imprevisível, dificultando planejamento e execução das obras. Por essa razão, uma nova abordagem foi proposta baseada em amplitudes cíclicas crescentes. Um modelo de dano acumulado estabeleceu a relação entre os ensaios com amplitude cíclica constante e cíclica. A nova abordagem fornece informações adicionais do comportamento cíclico da interface, como o efeito de ciclos anteriores, amplitude cíclica na ruptura e o acúmulo de deslocamento permanente. Essa nova abordagem pode ser facilmente aplicada em outras investigações experimentais e provas de cargas cíclicas. Do ponto de vista prática, essa abordagem pode reduzir o custo e tempo de projetos, além de melhorar a previsão do desempenho dessas fundações. Espera-se que essa pesquisa tenha trazido avanços para as empresas do setor e comunidade geotécnica. Contudo, novas pesquisas sobre fundações de torres eólicas onshore ainda são necessárias.

Shear-wall dominant multi-story reinforced concrete structures, constructed by using a special tunnel form technique are commonly built in countries facing a substantial seismic risk, such as Chile, Japan, Italy and Turkey. In 1999, two severe urban earthquakes struck Kocaeli and D&uuml / zce provinces in Turkey with magnitudes (Mw) 7.4 and 7.1, respectively. These catastrophes caused substantial structural damage, casualties and loss of lives. In the aftermath of these destructive earthquakes, neither demolished nor damaged shear-wall dominant buildings constructed by tunnel form techniques were reported. In spite of their high resistance to earthquake excitations, current seismic code provisions including the Uniform Building Code and the Turkish Seismic Code present limited information for their design criteria. This study presents experimental investigation of the panel unit having H-geometry. To investigate the seismic behavior of panel buildings, two prototype test specimens which have H wall design were tested at the Structural Mechanics Laboratory at METU. The experimental work involves the testing of two four-story, 1/5-scale reinforced concrete panel form building test specimens under lateral reversed loading, simulating the seismic forces and free vibration tests. Free vibration tests before and after cracking were done to assess the differences between the dynamic properties of uncracked and cracked test specimens. A moment-curvature program named Waller2002 for shear walls is developed to include the effects of steel strain hardening, confinement of concrete and tension strength of concrete. The moment-curvature relationships of panel form test specimens showed that walls with very low longitudinal steel ratios exhibit a brittle flexural failure with very little energy absorption. Shear walls of panel form test specimens have a reinforcement ratio of 0.0015 in the longitudinal and vertical directions. Under gradually increasing reversed lateral loading, the test specimens reached ultimate strength, as soon as the concrete cracked, followed by yielding and then rupturing of the longitudinal steel. The displacement ductility of the panel form test specimens was found to be very low. Thus, the occurrence of rupture of the longitudinal steel, as also observed in analytical studies, has been experimentally verified. Strength, stiffness, energy dissipation and story drifts of the test specimens were examined by evaluating the test results.

Prior experimental research clearly reveals that the performance of reinforced concrete frame structures under earthquake loading is closely related to the behavior of beam-to-column connection regions. In order for a reinforced concrete building to have an adequate response under high lateral deformations, beam-to-column connections should be able to preserve their integrity. However, even today beam-to-column connections are assumed to be rigid or elastic, leading to an incorrect estimation of the structural response under earthquake loading. One of the basic reasons for the assumption of rigid joints is the lack of analytical models that adequately represent the seismic behavior of the connection region. In this thesis, an analytical model that realistically represents the beam-to-column connection response is developed, in the light of prior experimental data. The experimental subassemblies used in the generation of the analytical model are later modeled in OpenSees environment in order to verify the accuracy of the model. Throughout the research, utmost attention is paid for the model to be simple enough to be used practically and also to cover a wide range of beam to column connection properties.

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The ability to adjust structural response to external loading and ensure structural safety and serviceability is a characteristic of Smart Systems. The key to achieving this is through the development and implementation of smart materials. An example of a smart material is a Shape Memory Alloy (SMA). Reinforced concrete structures are designed to sustain severe damage and permanent displacement during strong earthquakes, while maintaining their integrity, and safeguarding against loss of life. The design philosophy of dissipating the energy of major earthquakes leads to significant strains in the steel reinforcement and, consequently, damage in the plastic hinge zones. Most of the steel strain is permanent, thus leading to large residual deformations that can render the structure unserviceable after the earthquake. Alternative reinforcing materials such as superelastic SMAs offer strain recovery upon unloading, which may result in improved post-earthquake recovery. Shape Memory Alloys have the ability to dissipate energy through repeated cycling without significant degradation or permanent deformation. Superelastic SMAs possess stable hysteretic behavior over a certain range of temperature, where its shape is recoverable upon removal of load. Alternatively, Martensite SMAs also possess the ability to recover its shape through heating. Both types of SMA demonstrate promise in civil infrastructure applications, specifically in seismic-resistant design and retrofit of structures. The primary objective of this research is to investigate experimentally the performance of concrete beams and shear walls reinforced with superelastic SMAs in plastic hinge regions. Furthermore, this research program involves complementary numerical studies and the development of a proposed hysteretic constitutive model for superelastic SMAs applicable for nonlinear finite element analysis. The model considers the unique characteristics of the cyclic response of superelastic materials.