Dissertations / Theses on the topic 'Tubular construction'

Orientadores: Newton de Oliveira Pinto Júnior, João Alberto Venegas Requena
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo
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Resumo: As treliças mistas em aço-concreto, alternativas bastante eficientes para vencer grandes vãos, são geralmente empregadas em edifícios comerciais e industriais, e, em pontes ferroviárias e rodoviárias. Em muitos casos, para que se possibilite a passagem de dutos, dificultada nos quadros com presença de diagonais, e construído um painel Vierendeel central; porem, em algumas situações, este único painel pode ser insuficiente, necessitando-se então a criação de novos painéis para satisfazer o uso que se pretende dar a construção. Neste sentido, o objetivo do estudo foi determinar através de um procedimento de calculo analítico e modelagens elástica bi-dimensional e plástica tri-dimensional, a capacidade resistente e o modo de ruptura de uma treliça tubular mista bi-apoiados com 15 metros de vão, sendo todo o terço central constituído por painéis Vierendeel. Em seguida, mantendo-se o vão de 15 metros e os perfis estipulados no dimensionamento, foi feita uma parametrização dos resultados para estruturas com 3, 7, 9 e 13 painéis. O estudo, desenvolvido para cargas de escritório, apontou a proporção vão/3 - vão/3 - vão/3 como a ideal para a relação entre trechos treliçado - Vierendeel - treliçado, pois ao se aumentar a proporção do trecho central ocupado pelos painéis Vierendeel, os novos sistemas perdem muita rigidez passando a não suportar mais a carga estipulada no projeto. Alem disso, podem passar a apresentar deslocamentos verticais excessivos e resistência às forcas cortantes externas atuantes sobre os painéis insuficiente
Abstract: The steel-concrete composite trusses, an efficient alternative to overcome large spans, are generally used in commercial and industrial buildings, and rail and road bridges. In many cases, in order to enable the passage of ducts, with complications in the frames with the presence of diagonals, a central Vierendeel panel is built, but in some situations, if this single panel may be insufficient, then one would need to create new panels to meet the intended use to build. In this case, the objective of the study was to determine, through analytical calculation, two-dimensional elastic modeling and three-dimensional plastic modeling, the bearing capacity and failure mode of a bi-supported truss with a 15 meter span, and the entire central third consisting of Vierendeel panels. Then, keeping the span of 15 meters and the sections determined in the design, a parameterization of the results was made for structures having 3, 7, 9 and 13 panels. The study developed for office loads, found the proportion span/3 - span/3 - span/3, as the ideal relationship for the truss - Vierendeel - truss lengths, because by increasing the proportion of the length occupied by the central Vierendeel panels, the new system loses stiffness and no longer support the load stipulated in the project. Furthermore, they can start presenting excessive vertical displacements and insufficient resistance to external shear forces acting on the panels
Doutorado
Estruturas
Doutor em Engenharia Civil

The innovation of natural daylighting light pipe took place more than twenty years ago. Since then its daylighting performance has been reported in a number of studies. To date, however, no mathematical method that includes the effect of straight-run and bends within light pipes has been made available. Therefore, a generalm athematicalm odel for light pipes is desirablet o assessa nd predict its daylighting performance.F urthermore,s uch a generalm odel can enablet he assessmenot f light pipe system's efficiency and potential in energy saving. A modified form of daylight factor, Daylight Penetration Factor (DPF), has been introduced to build a sophisticated model that takes account of the effect of both internal and external environmental factors, and light pipe configuration. Measurementsa nd mathematicalm odelling activities aimed at predicting the daylighting performance of light pipes with various configurations under all weather conditions in the UK were undertaken. A general daylighting performance model, namely DPF model, for light pipes was developed and validated. The model enables estimation of daylight provision of the light pipes with a high degree of accuracy, i. e. R2 values of 0.95 and 0.97 for regression between predicted and measured illuminance were respectively obtained for the above model. The DPF model uses the most routinely measured radiation data, i. e. the global illuminance as input. Considering that in real applications, light pipes installed in a particular building may not receive the full amount of global illuminance as measured by local meteorological office. This may be due to partial shading of the light pipe top collector dome. Therefore, to enable the application of the DPF model in practical exercisesf undamentalw ork on sky diffuse illuminance measurementsh ave been undertaken. An exhaustive validation has been carried out to examine the DPF model in terms of the structure of the model and its performance. The DPF model was compared against studies by other independent researchersin the field. Independentd ata setsg atheredf rom a separates ite were used to validate the performance of the DPF model. Comprehensive statistical methods have been applied during the course of validation. Relevant, brief economic and environmental impact of the technology under discussion has also been undertaken. One of the main achievementso f this work is the mathematicalm ethod developedt o evaluatet he daylighting performance of light pipes. T'he other main achievement of this work is the development and validation of the DPF models for predicting light pipes' daylighting performance.

A design for a novel tubular high-precision direct-drive brushless linear motor has been developed. The novelty of the design lies in the orientation of the magnets in the mover. In conventional linear motors the magnets of the armature are arranged such that the attractive poles are adjacent throughout, in an NS-NS-NS orientation, where N denotes the north pole and S denotes the south pole of the magnet. In the new design, the magnets in the moving part are oriented in an NS-NS-SN-SN orientation. This change in orientation yields greater magnetic field intensity near the like-pole region. The magnets of the mover are encased within a brass tube, which slides through a three-phase array of current-carrying coils. As the coils are powered, they induce a force on the permanent magnets according to the Lorentz force equation. The primary advantages of the motor are its compact nature, fast, precise positioning due to its low-mass moving part, direct actuation, extended travel range, and ability to extend beyond its base. The linear motor is used in conjunction with a position sensor, power amplifiers, and a controller to form a complete solution for positioning and actuation requirements. Controllers were developed for two applications, with a lead-lag as the backbone of each. For the first application, the principal requirements are for fast rise and settling times. For the second application, the primary requirement is for near-zero overshoot. With the controller for application 1, the motor has a rise time of 55 ms, a settling time of 600 ms, and 65% overshoot. With the controller for application 2 implemented, the motor has a rise time of 1 s, a settling time of 2.5 s, and 0.2% overshoot. The maximum force capability of the motor is measured to be 26.4 N. The positioning resolution is 35 ?m. This thesis discusses the motor's physical design, construction, implementation, testing, and tuning. It includes specifications of the components of the motor and other necessary equipment, desired and actual motor performance, and the primary limitations on the precision of the system.

This thesis proposes two forms of external confinement for concrete filled steel tubular (CFST) columns. The confinement efficiency is studied by examining the axial strength enhancement and ductility improvement of the CFST columns with external confinement. Due to the heavy demand of confining steel to restore the column ductility in seismic regions, it is more efficient to confine these columns by hollow steel tube to form CFST column. Compared with transverse reinforcing steel, steel tube provides a stronger and more uniform confining pressure to the concrete core, and reduces the steel congestion problem for better concrete placing quality. The CFST columns are therefore characterised by higher strength, ductility and large energy absorption before failure. However, a major shortcoming of CFST columns is the imperfect steelconcrete interface bonding occurred at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confining effect and decreases the elastic modulus. To resolve the problem, it is proposed in this thesis to use external steel confinement in the forms of rings and ties to restrict the dilation of steel tube. For verification, a series of uni-axial compression test was performed on some CFST columns with external steel rings and ties. From the results, it was found that the external steel rings could improve both the axial strength and stiffness of the CFST columns significantly. However, the steel ties could not improve either the axial strength or elastic stiffness significantly. The confining efficiency was then investigated by comparing the strength of these confined-CFST columns with the reinforced concrete (RC) columns counterparts with the same concrete and steel volume. It is evident that the axial strength of CFST columns is much higher than the RC columns, which suggests that the application of CFST columns can utilise less construction materials and reduce the demolition waste. A theoretical model is also proposed for predicting the axial strength of ring-confined CFST columns. Comparison between the predicted results and the test results obtained by the author and other researchers shows that the proposed model gives good estimation for both unconfined and confined CFST columns.
published_or_final_version
Civil Engineering
Master
Master of Philosophy

Design of new evolution steel welded tubular frame specified for Formula Student series is the main goal of this thesis. In the first instance, type of frame designs is described. Next part of thesis is devote to rules, which must be respected in designing of new evolution of tubular frame. In main part, construction design and calculations of torsional stiffness using MKP analysis are mentioned. Interesting point of this work is located at penultimate part, which deals with preparation of tubular frame production. This is integral part of the construction process at all. Thesis ends with project summary.

Pour vérifier le comportement des liaisons tubulaires soudées, étude d'un système de mesure en temps réel des déformations sur la section nominale des tubes arrivant aux noeuds ; technologiquement le système est conçu à partir des matériels existants.

This diploma thesis deals with design load bearing steel structure of the sport stadium roofing with 82,8 m length and 29,0 m width. Roofing structure is designed and examined in two versions. Variant A is designed like tubular truss girder with axis distance 4,6 m. Variant B is designed like welded solid-web girder with same axis distance. These versions are compared by weight, manufacturing complexity and appearance, prefeable version is processed in detail. Drawings contain layout of both versions and manufacturing drawings of truss.

This diploma thesis deals with design of the supporting steel structure of the building of the exhibition pavilion with 84 m length and 30 m width. Roofing structure is designed and examined in two versions. Variant A is designed like tubular truss girder with axis distance 6 m. Variant B is also designed like tubular truss girder, but with different look, with same axis distance. These versions are compared by weight, manufacturing complexity and appearance, preferable version is processed in detail. Drawing documentation includes an anchor plan, layout structure and truss production drawing.

This diploma thesis deals with design load bearing steel structure of the sport stadium roofing with 67,2 m length and 28,8 m width. Roofing structure is designed and examined in two versions. Variant A is designed like tubular truss girder with axis distance 4,8 m. Variant B is designed like welded solid-web girder with same axis distance. These versions are compared by weight, manufacturing complexity and appearance, preferable version is processed in detail. Drawings contain layout of both versions and manufacturing drawings of truss.

Orientador: João Alberto Venegas Requena
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo
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Resumo: Este artigo apresenta o estudo da influência das ligações no comportamento das estruturas treliçadas compostas por perfis tubulares de aço. As ligações em treliças de aço são normalmente projetadas para união de barras por meio de chapas que garantam a transmissão e equilíbrio das forças. No caso em particular de treliças que utilizam perfis tubulares de aço as ligações são projetadas sem chapas. As barras são unidas diretamente por meio de soldas nos contatos dos perfis que são cortados geometricamente exatos para o ajuste da ligação. Este procedimento aumenta a produtividade de fabricação além de dar um aspecto visual melhor para a estrutura. Dependendo da geometria da ligação podem ocorrer excentricidades dos eixos provocando a introdução de momentos fletores, que quando não puderem ser evitados, devem ser levados em consideração não só no cálculo da ligação como também na determinação dos esforços da treliça. Outro aspecto importante é a análise do colapso da ligação que pode ocorrer quando uma barra é associada à outra de forma inadequada na ligação direta, sendo variados os tipos de falhas. Portanto, será analisada a influência das ligações no comportamento da estrutura a partir de gráficos baseado no estudo das equações de força resistente das ligações tubulares circulares. Este estudo gráfico permitiu a criação do processo de cálculo, denominado Processo Simplificado, que orientam para as combinações de perfis que atendam as exigências geométricas e de força resistente das ligações durante o dimensionamento de barras. O processo é baseado em de tabelas de cálculo desenvolvidas para a orientação de um bom projeto de estrutura treliçada considerando ou evitando estas influências sem onerar o projeto final
Abstract: This paper presents the study of connections influence in the behavior of hollow sections truss structures. Joints in steel trusses are usually designed considering sheets that will ensure the transmission and balance of forces. In particular case of trusses using hollow sections steel connections are designed without plates. The beams are directly welded to steel sections which are geometrically cut to fit the joint. This increases manufacturing productivity in addition to give the structure a better visual appearance. Axes eccentricities can occur depending on connection geometry resulting in introduction of bending moments. When this eccentricity cannot be avoided, it has to be taken into account in joint design and also in determining truss efforts. Another important aspect is analysis joint collapse which can occur when a beam is improperly associated to another beam, which can produce many kinds of fails. Therefore, graphics analyses were studied based on circular hollow sections joint strength equations that show the influence of joints on structures. The Simplified Process, created after graphics studies, shows the valid combinations of circular hollow sections geometry and strength during beam structure design verification. This process is based on tables developed to orient a good truss project considering or avoiding this influences without raising budget on final design
Mestrado
Estruturas e Geotécnica
Mestra em Engenharia Civil

En los últimos años la utilización de perfiles tubulares de acero rellenos de hormigón (CFT) se ha incrementado debido a su excelente comportamiento frente al sismo, alta resistencia, alta ductilidad y la gran capacidad de absorción de energía. Aunque España y en particular la Comunidad Valenciana no son zonas de riesgo sísmico elevado, el uso de este tipo de pilares ofrece también otras ventajas, como por ejemplo el incremento en la velocidad del proceso de construcción, la posibilidad de estandarización de las uniones y lo que es muy importante, una mayor resistencia al fuego. Por otra parte, el uso del hormigón de alta resistencia (HSC) en la construcción de estructuras de hormigón se está generalizando gracias al abaratamiento de su tecnología. La utilización de este material presenta enormes ventajas, sobre todo en elementos sometidos a axiles de compresión importantes, como ocurre en el caso de soportes de edificación o de pilas de puente. Sin embargo, el Eurocódigo 4, con el que de diseñan estas estructuras mixtas, queda limitado a hormigones de hasta 60 MPa. Dada la mayor resistencia seccional de las columnas CFT rellenas de HSC, es posible reducir su sección, para un mismo nivel de carga. De esta forma la esbeltez y los efectos de segundo orden cobran más importancia. En esta tesis doctoral se estudia el comportamiento de las columnas de acero, esbeltas, de sección circular, rellenas de hormigón de alta resistencia. Para ello se ha desarrollado una campaña experimental que ha sido ampliada con modelos numéricos. Se ha comprobado la validez del Eurocódigo 4 y se ha realizado un estudio paramétrico de las variables que influyen en la respuesta de estas columnas.

Le fonctionnement des airbags est soumis à des règles draconiennes de sécurité vis-à-vis des occupants du véhicule. Dans cette étude, le modèle est un tube à paroi mince fermé à ses deux extrémités par des sertis et percé d'orifices pour l'évacuation des gaz de combustion. Avant sa mise sur le marché, le système pyrotechnique subit des essais de validation. Le dernier (burst test) consiste à soumettre la chambre de combustion du générateur de gaz (GG) à des rampes de pression dynamique conduisant à la rupture de la structure. L’objectif est d'optimiser la conception des GG via la simulation numérique afin de rendre plus efficace et moins coûteuse en essais réels la phase de développement. On s’intéresse ici à la réponse dissipative du matériau constituant les GG au cours du burst test induit par un chargement dynamique. On étudie particulièrement Le mode de rupture par endommagement plastique ductile. Pour l’obtention de résultats expérimentaux exploitables, une étude numérique préliminaire est réalisée afin d’optimiser différentes géométries d’éprouvettes courbes (usinées dans un tube) en termes de champs de contraintes et de déformations dans les sections utiles. La campagne expérimentale montre une influence significative de l’écrouissage plastique, de la viscosité ainsi que de l’endommagement plastique ductile. Le modèle GTN est utilisé pour décrire les effets combinés mentionnés précédemment, incluant la germination et la croissance de cavités. Des simulations numériques du burst test sont enfin réalisées à l’aide du code de calcul industriel ABAQUS. La confrontation des résultats numériques et expérimentaux est encourageante concernant la prédiction du modèle
Airbag inflator functioning is submitted to draconian safety rules for vehicle occupants. In this study, the inflator structure is a thin tube closed at both extremities, crimped and perforated with exit ports for combustion gas release. Prior to manufacturing, the pyrotechnic system undergoes validation (burst) tests. The latter consist in putting inflator combustion chamber under various dynamic pressure ramps until structure failure. This work aims at increasing the efficiency and at reducing validation tests number by using numerical simulation. In this work, we are interested in the numerical description of the dissipative response of the inflator material during the burst test induced by dynamic loading. The failure mode under ductile plastic damage is particularly studied. For obtaining reliable experimental results, a preliminary numerical study is carried out for optimising the geometry of curved samples (machined in thin small diameter tubes) regarding strain and stress fields in the gage length. The experimental campaign shows significant influence of strain hardening, plastic viscosity and ductile damage on inflator material behaviour. The GTN damage-plasticity model is used to describe the combined aforementioned effects, including cavity nucleation and growth laws as well as viscous plasticity potential. Numerical simulations considering the validation burst test problem is performed employing the engineering calculation code ABAQUS. Confrontation of numerical results with experimental ones is encouraging concerning prediction ability of the model

Student Number : 9306442N - PhD thesis - School of Electrical and Information Engineering - Faculty of Engineering and the Built Environment
This thesis describes the design, construction and evaluation of a prototype modified tubular linear synchronous motor. The linear motor has a long static primary and a short permanent magnet mobile secondary. The design is unique in that a tubular topology has been modified to allow access to the moving secondary section. This modification means that this design can be used in long distance applications. The application for this research is the use of linear motors in rope-less vertical trans- portation systems in ultra deep level mines. The design of the linear motor has been analysed from an electrical, magnetic, mechanical and thermal perspective. Finite Element Analysis was used to predict the performance of the linear motor. The design of the secondary section has been optimised to produce the greatest possible thrust force while reducing the effects of the cogging forces. The linear motor has been tested extensively and the results correlate with theoretical predictions from the Finite Element Analysis. This project proves that the modified tubular lin- ear synchronous motor is a viable technology that can be used in rope-less vertical transportation systems.

博士
逢甲大學
纖維與複合材料學系
104
Vascular grafts are used to replace the impaired native blood vessels, and thus play a significant role in clinical surgery. Making small-diameter vascular grafts that have a match in mechanical properties of blood vessels thus become challenging. Therefore, this study aims to develop composite tubular that possess the comparable mechanical properties to that of blood vessels. The effects of yarn types, tubular knit types, the freeze-thaw cycles of polyvinyl alcohol (PVA), and the drying time of the thawing on the mechanical properties of composite tubular are evaluated in order to assess the implant effectiveness of these composite tubular. Five different wrap yarns are first tested in terms of thermal treatment and twist coefficients, followed by being made into tubular braids, tubular warp knits, and tubular weft knits. Next, PVA hydrogels are combined with the tubular fabrics via casting, after which they are freeze-thawed different cycles with different drying times of thawing. The different composite tubular are evaluated for their mechanical properties. The results indicate that with a thermal treatment temperature of 160 ˚C, the PET/spandex wrap yarn have an elongation that is 86% lower than that of the untreated groups. An increasing thermal treatment temperature results in a decrease in the stress decay and permanent deformation of the PET/spandex wrap yarns. Moreover, an increasing thermal treatment temperature also decreases the shrinkage level of the spandex fibers, and thereby stabilizes the tubular fabrics. The porosity of the tubular fabrics is not dependent on the thermal treatment temperature and yarn types. The tensile strength and elongation of tubular knits are higher than the tensile strength and elongation of the tubular braids. More freeze-thaw cycles lead to a lower compliance, but also a higher bursting strength of vascular grafts, while the combination of spandex fibers improves the compliance of the fabrics and composite tubular. Increasing the drying time for PVA hydrogels is favorable to the compressive strength, bursting strength, and suture retention, while being remarkably adverse to the compliance of the vascular grafts. The warp-knit composite tubular have a higher axial shrinkage when they are circumferentially extended. The weft-knit composite tubular outperform the warp-knit composite tubular in terms of compressive strength, bursting strength and suture retention.

M. Tech (Biosciences, Faculty of Applied and Computer Sciences), Vaal University of Technology.
The mass production of algae for commercial purposes has predominately been carried out in open ponds systems. However, open ponds systems have a number of disadvantages such as poor light utilization, requirement for large areas of land and high risks of contamination. On the other hand, photobioreactors have attracted much interest because they allow a better control of the cultivation conditions than open systems. With photobioreactors, higher biomass productivities are obtained and contamination can be easily prevented. Photobioreactors can also be engineered to manipulate the light and dark photosynthetic reactions thus enhancing biomass productivity. The main objective of this study was to construct a novel tubular photobioreactor which had the ability to expose the cultured alga to light and dark phases with the aim of optimizing the algal biomass production. A novel tubular photobioreactor with the ability to manipulate the cultured alga’s light and dark photosynthetic reactions was constructed in this study. The alga Spirulina platensis was chosen as the test organism in this novel tubular photobioreactor due to a number of reasons such as its globally socioeconomic importance, its tolerance of higher pH and temperature values which makes it almost impossible to contaminate. The cultivation process of Spirulina in the photobioreactor was investigated through alternating light and dark cycles in an attempt to increase the photosynthetic efficiency of the culture. The effect of different light intensities on the growth of Spirulina in the novel tubular photobioreactor was investigated and it was found that the best light condition that favored higher biomass formation was at 600 μ mol m-2 s-1. Five different light/ dark ratios were evaluated at a light intensity of 600 μ mol m-2 s-1 during a batch mode of operation of the novel tubular photobioreactor. The light/ dark ratio of 1:0.25 was found to be the best ratio because it gave the highest biomass in the shortest period of time when compared to the other ratios used. These results seem to suggest that longer light cycle relative to dark cycle results in higher biomass production. The ratio of 1:0.25 was then used to operate the novel tubular photobioreactor in a continuous mode. A maximum biomass productivity of 25 g/m2/day was achieved which corresponded to a net photosynthetic efficiency of 5.7 %. This result was found to be higher than what most photobioreactors could achieve but it was 2.8 g/m2/day lower than the highest ever reported productivity in a photobioreactor when Spirulina is cultivated. The 2.8 g/m2/day lower was attributed to the different materials used in the construction of these two photobioreactors. The photobioreactor which achieved 27.8 g/m2/day was made up of a clear glass whereas the novel tubular photobioreactor was made up of a PVC tubing. PVC tubes tend to change from clear to a milky colour after a certain period when it is used at higher temperature and pH values hence blocks a certain amount of light. Therefore the main recommendation in this study is to use a PVC tubing with a longer life span when used at a higher temperature and pH values.

Indiana University-Purdue University Indianapolis (IUPUI)
Crashworthiness design is gaining more importance in the automotive industry due to high competition and tight safety norms. Further there is a need for light weight structures in the automotive design. Structural optimization in last two decades have been widely explored to improve existing designs or conceive new designs with better crashworthiness and reduced mass. Although many gradient based and heuristic methods for topology and topometry based crashworthiness design are available these days, most of them result in stiff structures that are suitable only for a set of vehicle components in which maximizing the energy absorption or minimizing the intrusion is the main concern. However, there are some other components in a vehicle structure that should have characteristics of both stiffness and flexibility. Moreover, the load paths within the structure and potential buckle modes also play an important role in efficient functioning of such components. For example, the front bumper, side frame rails, steering column, and occupant protection devices like the knee bolster should all exhibit controlled deformation and collapse behavior. This investigation introduces a methodology to design dynamically crushed thin-walled tubular structures for crashworthiness applications. Due to their low cost, high energy absorption efficiency, and capacity to withstand long strokes, thin-walled tubular structures are extensively used in the automotive industry. Tubular structures subjected to impact loading may undergo three modes of deformation: progressive crushing/buckling, dynamic plastic buckling, and global bending or Euler-type buckling. Of these, progressive buckling is the most desirable mode of collapse because it leads to a desirable deformation characteristic, low peak reaction force, and higher energy absorption efficiency. Progressive buckling is generally observed under pure axial loading; however, during an actual crash event, tubular structures are often subjected to oblique impact loads in which Euler-type buckling is the dominating mode of deformation. This undesired behavior severely reduces the energy absorption capability of the tubular structure. The design methodology presented in this paper relies on the ability of a compliant mechanism to transfer displacement and/or force from an input to desired output port locations. The suitable output port locations are utilized to enforce desired buckle zones, mitigating the natural Euler-type buckling effect. The problem addressed in this investigation is to find the thickness distribution of a thin-walled structure and the output port locations that maximizes the energy absorption while maintaining the peak reaction force at a prescribed limit. The underlying design for thickness distribution follows a uniform mutual potential energy density under a dynamic impact event. Nonlinear explicit finite element code LS-DYNA is used to simulate tubular structures under crash loading. Biologically inspired hybrid cellular automaton (HCA) method is used to drive the design process. Results are demonstrated on long straight and S-rail tubes subject to oblique loading, achieving progressive crushing in most cases.

This paper presents the behaviour and design of axially loaded concrete filled stainless steel circular and square hollow sections. The experimental investigation was conducted using different concrete cube strengths varied from 30 to 100 MPa. The column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with existing design methods for composite carbon steel sections ¿ Eurocode 4 and ACI. It was found that existing design guidance for carbon steel may generally be safely applied to concrete filled stainless steel tubes, though it tends to be over-conservative. A continuous strength method is proposed and it is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance.

Dissertação de Mestrado em Construção Metálica e Mista apresentada à Faculdade de Ciências e Tecnologia
A necessidade de combater o aquecimento global tem levado a um maior interesse pelas energias renováveis ​​e, consequentemente, a indústria eólica está passando por um desenvolvimento próspero e avanço que surge como um apelo da estratégia global de energia e questão ambiental. Um dos desafios mais críticos para a turbina eólica onshore envolve o projeto ideal da estrutura de suporte, incluindo a torre da fundação e da turbina. Com o desenvolvimento da indústria de energia eólica onshore para altitudes mais elevadas, o novo conceito estrutural de suporte pode ser comprovado ser mais vantajoso do que os tipos convencionais quando comparado em termos de custo, segurança, procedimento de montagem inovador, baixa manutenção e aspectos ambientais. Para tratar deste problema foi proposta uma nova solução de torre híbrida. A solução é direcionada para altas aplicações onshore que são mais eficazes na geração de energia em situações em que o perfil de cisalhamento do vento está claramente beneficiando turbinas mais altas. Torres híbridas em forma de rede tubular requerem uma peça de transição que serve como uma conexão entre treliça e partes tubulares. Como a peça de transição é suposto transferir todas as cargas dinâmicas e auto-peso para a rede e fundação, esses elementos estruturais apresentam características únicas e são componentes críticos para projetar e deve resistir a fortes momentos de flexão cíclica, forças de cisalhamento e cargas axiais. As peças de transição bem projetadas com otimizado estado final e capacidades de fadiga para a fabricação, contribuem para a solidez estrutural, confiabilidade e praticabilidade de novas turbinas eólicas onshore torres híbridas.Esta pesquisa centra-se principalmente na concepção e investigação da peça de transição para uma turbina eólica 5MW onshore Híbrida como referência. Usando as cargas simuladas a partir de simulações aero-elásticas e considerando os requisitos geométricos, funcionais e mecânicos, a peça de transição foi projetada para o estado limite final, considerando as não-linearidades e imperfeições incluídas no modelo de elementos finitos. Diferentes estudos de caso foram apresentados nesta tese com o objetivo de explorar diferentes possibilidades e ampliar o conceito de pesquisa. Além disso, analisá-los e compará-los com base na funcionalidade e economia nos dá maior senso de escolher uma opção viável. Nesta pesquisa, principalmente, o foco foi analisar a solução usando um reforço, peça de transição usando diferentes tipos de aço em diferentes seções, usando apenas de aço macio grau e apenas utilizando aço de alta resistência. Utilizou-se uma metodologia de simulação para prever a vida de fadiga da peça de transição, realizando a análise ELISA elástica e importando as tensões resultantes para o software de previsão da fadiga. Uma simulação de tensão multi-axial é então realizada para determinar pontos de fadiga mais realistas e tempo de vida da peça de transição. Prevê-se que uma abordagem mais probabilística deve ser utilizada para a previsão da vida de fadiga, em que a velocidade do vento está em constante mudança durante a vida útil, neste caso apenas as condições de vento extremo foram estudadas.
With the emerging concept of sustainable constructions, the need to fight global warming has led to increased interest in renewable energies and consequently, wind industry is undergoing prosperous development and advancement which comes out as a call of global energy strategy and environmental issue. One of the most critical challenges for onshore wind turbine involves the optimal design of support structure including foundation and turbine tower. With the development of onshore wind industry heading for higher altitudes, new support structural concept might be proven to be more advantageous than conventional types when comparing in terms of cost, safety, innovative erection procedure, low maintenance and environmental aspects. In order to deal with such a problem a new hybrid tower solution was proposed. The solution is targeted at tall onshore applications which are more effective in energy generation in situations where wind shear profile is clearly benefiting higher turbines.Hybrid lattice-tubular towers requires a transition piece which serves as a connection between lattice and tubular parts. As the transition piece is supposed to transfer all the dynamic and self-weight loads to the lattice and foundation, these structural elements present unique features and are critical components to design and ought to resist strong cyclic bending moments, shear forces and axial loads. Well-designed transition pieces with optimized ultimate state and fatigue capacities for manufacturing, contribute to the structural soundness, reliability and practicability of new onshore wind turbines hybrid towers.This research mainly focuses on design and investigation of the transition piece for an onshore 5MW wind turbine hybrid tower as a reference. Using the simulated loads from an aero-elastic simulations and considering the geometrical, functional and mechanical requirements the transition piece was designed for ultimate limit state with considering nonlinearities and imperfections included into the finite element model. Different case studies were presented in this thesis with the aim to exploit different possibilities and broader the concept of research. Furthermore, analyzing and comparing them on the basis of functionality and economics gives us greater sense of picking a viable option. In this research mainly the focus was to analyse the solution using a stiffener, transition piece using different grades of steel in different sections, using only mild steel grade and just utilizing high strength steel. A simulation methodology for predicting the fatigue life of transition piece was used by performing elastic FEA analysis and importing the resulting stresses into the fatigue prediction software. A multi axial strain-life simulation is then performed to determine more realistic fatigue hot spots and life time of the transition piece. It is envisaged that more probabilistic approach should be used for fatigue life prediction, in which wind speed is constantly changing over service life as in this case only extreme wind conditions were studied.
Universidade de Coimbra - European Erasmus Mundus Master Course - 520121-1-2011-1-CZ-ERA MUNDUS-EMMC Sustainable Constructions under natural hazards and catastrophic events

This paper presents the details of an experimental investigation on the behaviour of axially loaded concrete-filled stainless steel elliptical hollow sections. The experimental investigation was conducted using normal and high strength concrete of 30 and 100 MPa. The current study is based on stub column tests and is therefore limited to cross-section capacity. Based on the equations proposed by the authors on concrete-filled stainless steel circular columns, a new set of equations for the stainless steel concrete-filled elliptical hollow sections were proposed. From the limited data currently available, the equation provides an accurate and consistent prediction of the axial capacity of the composite concrete-filled stainless steel elliptical hollow sections.