[pt] Neste trabalho, apresenta-se um estudo numérico e experimental sobre o comportamento estrutural de um módulo de ponte tensegrity para pedestres com materiais naturais. Inicialmente é apresentado o conceito de estruturas tensegrity, destacando-se seu surgimento e atual contexto, aplicações e estudos relacionados a este sistema estrutural. Também é apresentada a importância e os benefícios da utlização de materiais naturais na construção civil. Um projeto de ponte tensegrity para pedestres realizado previamente é selecionado como objeto de estudo. Com base em suas principais características, realiza-se um protótipo do módulo da ponte em escala 1:25. Propõe-se um método construtivo considerando técnicas ajustáveis para montagem e desmontagem. Posteriormente, um protótipo em escala de aproximadamente 1:6 é construído utilizando colmos de bambu da família Phyllostachys aurea para as estroncas e cordas de sisal para os cabos. O módulo é instrumentado e ensaiado estatica e dinamicamente a fim de avaliar a influência das perdas de pretensão por fluência e relaxação sobre o comportamento da estrutura. Os resultados obtidos dos ensaios experimentais são comparados com as previsões numéricas obtidas com auxílio de modelo computacional quanto às tensões atuantes e os modos de vibração. Através do cruzamento dos dados foi possível determinar indiretamente o nível de pretensão aplicado no módulo tensegrity e avaliar a perda de pretensão ao longo do tempo. As investigações estática e dinâmica apresentaram considerável afinidade. / [en] In this work, a theoretical and practical study of the behavior of a tensegrity based pedestrian bridge constructed with natural materials is presented. Initially it is shown the concept of tensegrity structures, highlighting its emergence and current context, applications within civil engineering and studies related to this structural system. The importance and benefits of using natural materials in civil construction are also presented. A pedestrian bridge design made using tensegrity structure is designated as study object and a prototype of the bridge s module is built in 1:25 scale. A constructive method is proposed considering deployable techniques for assembly and disassembly. Subsequently, a prototype on a 1: 6 scale is built using Phyllostachys aurea bamboo culms for the struts and sisal ropes for the cables. The module is instrumented and tested statically and dynamically in order to understand the processes of loss of prestress and creep on the structure s behavior. The results obtained from the experimental tests are compared with the numerical predictions obtained with the aid of a computational model regarding the stresses and the vibration modes. Through the crossing of the data it was possible to indirectly determine the level of prestress applied in the tensegrity module and to evaluate the loss of prestress over time. The static and dynamic investigations showed considerable affinity.

L’ingénierie tissulaire est une stratégie médicale qui repose sur la régénération de tissu par les cellules avec ou sans matériaux. Pour maîtriser cette synthèse, il faut comprendre la cellule comme une part intégrante du tissu. Hormis ses interactions biochimiques avec son support, la cellule interagit également mécaniquement avec son environnement. Elle s’accroche à ce dernier et évalue sa dureté pour adapter sa réponse biologique. Dans cette étude, j’ai développé des modèles numériques pour analyser l’influence de la rigidité du substrat sur le comportement mécanique de la cellule, sur sa structure contractile interne et les efforts qu’elle génère. En d’autres termes, j’ai essayé de comprendre comment la cellule ressent la rigidité de son environnement. De plus, au lieu de me focaliser sur les propriétés mécaniques quantitatives, j’ai cherché à développer un modèle conceptuel simplifié plus proche de la structure cellulaire. / Tissue engineering is a medical strategy based on utilizing cells and materials to regenerate a new tissue. Yet, it involves intertwined interactions that allow cells to act as integrated parts of an organ. In addition to chemical reactions, the cell interacts mechanically with its environment by sensing its rigidity. Here, we used several computational models to understand how substrate rigidity affects a cell’s structure as it adheres and spreads on it. In other words we tried to understand the way a cell feels how soft or hard it surrounding is, how it affects its internal structure and the forces that transit within it. In addition, instead of focusing on mechanical properties, we developed a simplified, yet coherent conceptual understanding of the cellular structure.

Vibration structural health monitoring (VHM) uses the vibration properties to evaluate many civil structures during the design steps, building steps and service life.The whole function, expressed by stiffness and frequencies of tensegrity structures are primarily related to the level of pre-stress. The present work investigates the possibilities to use this relation in designing, constructing and evaluating the tensegrity structures.One of the aims of the thesis was to improve the current models for resonance frequency simulation of tensegrities. This has been achieved by introducing the bending behaviour of all components, and by a one-way coupling between the axial force and the stiffness.The environmental temperature effects on vibration properties of tensegrity structures have been also  investigated. Changes in dynamic characteristics due to temperature variations were compared with the changes due to decreasing pre-tension in one of the cables. In general, it is shown that the change in structural frequencies coming from temperature changes could of several magnitude as those from damage.Coinciding natural frequencies and low stiffness are known issues of tensegrity structures. The former can be an obstacle in VHM, while the later normally limits their uses in real engineering applications. It has been shown that the optimum self-stress vector of tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others.The environmental temperature effects on vibration properties of tensegrity structures were revisited to find a solution such that the natural frequencies of the tensegrity structures are not strongly affected by the changes in the environmental temperature. An asymmetric self-stress vector can be chosen so that the criterion is fulfilled as well as possible. The level of pre-stress can also be regulated to achieve the solution. The last part of this thesis, services as a summary of the work. / <p>QC 20160429</p>

It is believed that structures and actuation systems should be tightly integrated together in the future to create fast moving, efficient, lightweight dynamic machines. Such actuated structures could be used for morphing aircraft wings, lightweight actuated space structures, or in robotics. This requires actuators to be distributed through the structure. A tensegrity structure is a very promising candidate for this future integration due to its potentially excellent stiffness and strength-to-weight ratio, and the inherent advantage of being a multi-element structure into which actuators can be embedded. Development of these machines will utilise expertise in several fields, involving kinematics, dynamics, actuation and multi-axis motion control. The research presented in this thesis concerns the study of multi-axis actuated tensegrity structures. A form-finding method has been developed to find stable geometries and determine stiffness properties of the type of tensegrity structure proposed. It has been shown that a tensegrity structure, with practical nodes of finite size, can be designed with actuated members to give shape-changing properties while potentially allowing a good stiffness to mass ratio. An antagonistic multi-axis control scheme has been developed for the tensegrity structure. The describing function technique has been used to analyse the dead band controller in the control scheme, giving a stability criterion. An experimental actuated tensegrity system has been designed and built incorporating pneumatic muscles controlled by switching valves. Mathematical models for the experimental actuated tensegrity system have been developed in detail, including the pneumatic actuation system and the structure geometry. The dynamic behaviour of the tensegrity system has been investigated via several simulation studies, using the developed models and the proposed control scheme. Experimental validation has been successfully conducted. The multi-axis control scheme can accurately control the tensegrity structure to achieve shape changes while maintaining a desired level of internal pre-load. The mathematical models can be used as a basis for further development.

The main goal of this research is to construct hierarchical microstructures from polymer nanocomposites. Specifically, the research focused on constructing tensegrity-inspired microstructure where the nanoparticles are the compression members and the polymer matrix is tensile web. In order to achieve the tensegrity-inpired microstruture, the research was conducted with the following objectives. 1. Synthesis of Hydroxyapatite (HAp) nanoparticles of controlled shapes using block copolymer templates. 2. Investigation of the effects of particle loadings and shapes on isotropic nanocomposite properties. 3. Construction of HAp building blocks into the tensegrity-inspired microstructures First, in order to use the nanoparticles for this structure, needle-shaped HAp nanoparticles were synthesized using block copolymer templates. The results indicated that significant amount of polymer remained on particle surface. Since these particles were coated with polymer blocks, the decorated polymer blocks were considered as the interphase material which would be used to prestress the HAp nanoparticles, and the particles would be acted as the building blocks for constructing tensegrity-inspired microstructure. For nanocomposites, polymer coating on HAp nanoparticles promoted particle dispersion. The effect of particle shapes on thermomechanical properties did not show significant differences between the two particle systems due to their low aspect ratios and chemical similarity. However, the polymer crystallinity and crystallization showed different trend as a function of particle loadings in two particle systems, and the behavior was unified through a common particle spacing of approximately 120 nm. In order to investigate the effect of particle arrangement in the polymer matrix, needle-shaped HAp nanoparticles synthesized with two different block copolymers were mixed with different morphology of polymer matrices and manipulated particle arrangement using the drawing process. Nanocomposites prepared with different matrix morphologies showed the similar dispersion characteristics and reinforcement behavior. The experimental results showed the drawing process influenced the particle arrangement in the polymer matrix, and the particle arrangement and reinforcement behavior were influenced by polymer matrix morphology. The thermomechanical properties of both matrix systems enhanced through the drawing process in the glassy region, but the effect of degree of particle orientation was difficult to distinguish due to low aspect ratios of HAp particles which was not enough to impact on overall microstructure.

Endothelial cells form the lining of the walls of blood vessels and are continuously subjected to mechanical stimuli from the blood flow. Microtubule-organizing center (MTOC),<br>also known as centrosome is a structure found in eukaryotic cells close to the nucleus. MTOC relocates relative to the nucleus when endothelial cells are exposed to shear stress which determines their polarization, thus it plays a critical role in cell migration and wound healing. The nuclear lamina, a mesh-like network that lies underneath the nuclear membrane, is composed of lamins, type V intermediate filament proteins. Mutations in LMNA gene that encodes A-type lamins cause the production of a mutant form of lamin A called progerin and leads to a rare premature aging disease known as Hutchinson-Gilford Progeria Syndrome<br><div>(HGPS). The goal of this study is to investigate how fluid flow affects the cytoskeleton of endothelial cells.</div><div><br></div>This thesis consists of two main sections; computational mechanical modeling and laboratory experimental work. The mechanical model was implemented using Ansys Workbench software as a tensegrity-based cellular model in order to simulate the state of an endothelial cell under the effects of induced shear stress from the blood fluid flow. This tensegrity-based cellular model - composed of a plasma membrane, cytoplasm, nucleus, microtubules, and<br><div>actin filaments - aims to understand the effects of the fluid flow on the mechanics of the cytoskeleton. In addition, the laboratory experiments conducted in this study examined the MTOC-nuclear orientation of endothelial cells under shear stress with the presence of wound healing. Wild-type lamin A and progerin-expressing BAECs were studied under static and sheared conditions.</div><div><br></div><div> Moreover, a custom MATLAB code was utilized to measure the MTOC-nuclear orientation</div>angle and classification. Results demonstrate that shear stress leads to different responses of the MTOC orientation between the wild-type and progerin-expressing cells around the vertical wound edge. Future directions for this study involve additional experimental work together with the improved simulation results to confirm the MTOC orientation<br>relative to the nucleus under shear stress.

This diploma thesis focuses on computational modeling of the cell mechanical tests. The goal of this thesis is to build a cell model and to simulate compression test on this model. If necessary, the model should be adjusted so the model reflects real cell behavior. It was created the cell model reflecting cytoplasm, nucleus, membrane and cell cytoskeleton. Cytoskeleton was modeled as tensegrity structure. After this, the pressure test was simulated on this model. The behavior of the cell model and real cell was compared using the stress force. The stress force - cell deformation curve was markedly different for the cell model and the real cell. For this reason, the cytoplasm material model was adjusted. The difference between the curves was acceptable after this modification. It was found during computations that the cytoskeleton model influence on the cell load is minimal. These results does not reflects real cell behavior, which means that the model is considered inadequate for performing stress load simulation.

Although the concept of tensegrity structures was invented in the beginning of the twentieth century, the applications of these structures are limited, partially due to their low stiffness. The stiffness of tensegrities comes from topology, configuration, pre-stress and initial axial element stiffnesses.  The first part of the present work is concerned with finding the magnitude of pre-stress. Its role in stiffness of tensegrity structures is to postpone the slackening of cables. A high pre-stress could result in instability of the structure due to buckling and yielding of compressive and tension elements, respectively. Tensegrity structures are subjected to various external loads such as self-weight, wind or snow loads which in turn could act in different directions and be of different magnitudes. Flexibility analysis is used to find the critical load combinations. The magnitude of pre-stress, in order to sustain large external loads, is obtained through flexibility figures, and flexibility ellipsoids are employed to ensure enough stiffness of the structure when disturbances are applied to a loaded structure.  It has been seen that the most flexible direction is very much sensitive to the pre-stress magnitude and neither analytical methods nor flexibility ellipsoids are able to find the most flexible directions. The flexibility figures from a non-linear analysis are here utilized to find the weak directions.  In the second part of the present work, a strategy is developed to compare tensegrity booms of triangular prism and Snelson types with a truss boom. It is found that tensegrity structures are less stiff than a truss boom when a transversal load is applied. An optimization approach is employed to find the placement of the actuators and their minimum length variations. The results show that the bending stiffness can be significantly improved, but still an active tensegrity boom is less stiff than a truss boom. Genetic algorithm shows high accuracy of searching non-structural space. / QC 20110524

The overall goal of this work is to improve the structural performance of cellular structures in bending applications by incorporating tensegrity behavior using long continuous fibers. The designs are inspired by the hierarchical cellular structure composition present in pomelo fruit and the structural behavior of tensegrity structures. A design method for analyzing and predicting the behavior of the structures is presented. A novel manufacturing method is developed to produce the cellular structures with tensegrity behavior through the combination additive manufacturing and metal casting techniques. Tensegrity structures provide high stiffness to mass ratio with all the comprising elements experiencing either tension or compression. This research investigates the possibility of integrating tensegrity behavior with cellular structure mechanics and provides a design procedure in this process. The placement of fibers in an octet cellular structure was determined such that tensegrity behavior was achieved. Furthermore, using finite element analysis the bending performance was evaluated and the influence of fibers was measured using the models. The overall decrease in bending stress was 66.6 %. Extending this analysis, a design strategy was established to help designers in selecting fiber diameter based on the dimensions and material properties such that the deflection of the overall structure can be controlled. This research looks to Additive Manufacturing (AM) as a means to introduce tensegrity behavior in cellular structures. By combining Binder Jetting and metal casting a controlled reliable process is shown to produce aluminum octet-cellular structures with embedded fibers. 3D-printed sand molds embedded with long continuous fibers were used for metal casting. The fabricated structures were then subjected to 4 point bending tests to evaluate the effects of tensegrity behavior on the cellular mechanics. Through this fabrication and testing process, this work addresses the gap of evaluating the performance of tensegrity behavior. The overall strength increase by 30%. The simulation and experimental results were then compared to show the predictability of this process with errors of 2% for octet structures without fibers and 6% for octet structures with fibers. / Master of Science

The purpose of this document is to study the application of Tensegrity principles on tensile textile constructions. This work studies the basic concept of Tensegrity unit, its classification according a previous researcher (Anthony Pugh) and the author’s contribution, focused on new generations of forms. Through the geometry and computer software, another typology and a constructive simple method is developed, bearing in mind, some aspects as important as system pretension to find its balance / El propósito de esta tesis es el estudio de la aplicación de los principios del tensegrity a las construcciones textiles atirantadas. El estudio del concepto básico de la unidad tensegrity, sus clasificaciones según investigadores anteriores (Anthony Pugh) y el aporte personal de nuevas generaciones de forma por medio de la geometría y programas informáticos, otra tipología y un método constructivo sencillo de realizar teniendo en cuenta aspectos tan importantes como la pretensión del sistema para buscar el equilibrio del mismo. La contribución clave de este prototipo en el campo de las estructuras ligeras es que es la primera vez que un anillo tensegrity ha sido utilizado en lugar de un anillo de compresión, para generar un domo completamente en tensegrity. Además se reemplazaron los tensores de los tensegritis tradicionales por membranas.