Análise estrutural de uma torre tubular sob acção do vento

Com a realização deste trabalho, pretende-se essencialmente dar a conhecer a influência que a acção do vento possui no dimensionamento de determinadas estruturas, neste caso específico, em torres tubulares de telecomunicações. É por todos sabido, da importância de um capaz e evoluído sistema de comunicações, no desenvolvimento sustentado do mundo moderno. Nesse sentido, o avanço galopante, principalmente nas últimas duas décadas, das tecnologias de Telecomunicações, implicou uma rápida resposta em consonância na implantação e proliferação de infraestruturas de suporte aos equipamentos dessas tecnologias. Assim, a estrutura em forma de torre tubular, entre as demais variadas secções que as constituem, foi adquirindo preponderância neste campo, constituindo a mais vasta utilização de estruturas de suporte aos equipamentos de telecomunicações, nomeadamente em meios rurais, onde escasseiam edificações com alturas suficientes para fazer face às necessidades das operadoras licenciadas para os devidos efeitos. Será efectuada uma breve descrição sobre as diversas e mais comuns tipologias de torres utilizadas no âmbito do suporte de equipamentos de telecomunicações. Descreve-se, em forma de relatório e levantamento fotográfico, a ocorrência do colapso de uma torre tubular de telecomunicações. Por último, e na sequência do incidente referido no ponto anterior, será efectuada com detalhe, a análise estrutural da torre tubular que foi instalada na posição da anteriormente instalada.

Reliability-based evaluation of design code provisions for circular concrete-filled steel columns

This paper presents an investigation of design code provisions for steel-concrete composite columns. The study covers the national building codes of United States, Canada and Brazil, and the transnational EUROCODE. The study is based on experimental results of 93 axially loaded concrete-filled tubular steel columns. This includes 36 unpublished, full scale experimental results by the authors and 57 results from the literature. The error of resistance models is determined by comparing experimental results for ultimate loads with code-predicted column resistances. Regression analysis is used to describe the variation of model error with column slenderness and to describe model uncertainty. The paper shows that Canadian and European codes are able to predict mean column resistance, since resistance models of these codes present detailed formulations for concrete confinement by a steel tube. ANSI/AISC and Brazilian codes have limited allowance for concrete confinement, and become very conservative for short columns. Reliability analysis is used to evaluate the safety level of code provisions. Reliability analysis includes model error and other random problem parameters like steel and concrete strengths, and dead and live loads. Design code provisions are evaluated in terms of sufficient and uniform reliability criteria. Results show that the four design codes studied provide uniform reliability, with the Canadian code being best in achieving this goal. This is a result of a well balanced code, both in terms of load combinations and resistance model. The European code is less successful in providing uniform reliability, a consequence of the partial factors used in load combinations. The paper also shows that reliability indexes of columns designed according to European code can be as low as 2.2, which is quite below target reliability levels of EUROCODE. (C) 2009 Elsevier Ltd. All rights reserved.

Rod length influence in torque measurement of SPT-T test

Since Ranzini suggested supplementing the SPT test with measurement of the torque required to turn the split spoon sampler after driving, many Brazilian engineers have been using this in the design of pile foundations. This paper presents a study of the rod length influence in the torque measurement. A theoretical study of material resistance considering torsion and bending in a thin wall tubular steel shaft was performed. It makes possible to conclude that the shearing tension caused by the proper weight represents less than 1% of the shearing tension caused by the turning moment. In addition, an experimental study was done with electric torquemeters fixed in a horizontal rod system. The tests were being carried out to analyze rods of one meter to twenty meters in length and the measurements were collected at the ends of each rod length verifying the efficiency data. As a result, it is possible to verify that the torque difference through rod length is lower than minimum scales of mechanical torquemeters that are used on practical engineering. Also a fact to be considered is a big torque loss for values under 20 N.m of applied torque. This way, the SPT-T is not adequate to low consistency soil. Copyright ASCE 2007.

A First approach on the new transmission system in northern Brazil

This article shows an analysis of the electrical parameters of a three-phase transmission line section using a relatively new design for steel towers characterized by 280 meters high. These main features, the height of the line conductors and distance between them, are intrinsically related to the longitudinal and transversal parameters of the line. By this means, an analysis was carried out in order to show the electrical variations between a transmission line using the new technology and a conventional 440-kV line through a wide range of frequencies and a variable soil resistivity. © 2012 The Institution of Engineering and Technology.

Introduction of a non-conventional solution for Amazon transmission system: Analysis of the electric aspects

This article shows an analysis of the longitudinal electric parameters of a three-phase transmission line/section using a 280-meter high steel tower. This characteristic, the height of the line conductors and distance between them, are intrinsic related to the longitudinal and transversal parameters of the line. By this means, an accurate study was carried out in order to show the electric variations between a transmission line using the new technology and a three-phase conventional 440 kV line for a wide range of frequencies and a variable soil resistivity. In addition, by using a digital line model, simulations are carried out in time domain to analyze critical overvoltage transients on the studied line. © 2011 IEEE.

Studio del comportamento flesso-torsionale di un telaio in materiale composito per vettura sportiva

Lo studio svolto in merito alle tecniche di produzione di componenti strutturali in materiale composito ha permesso il raggiungimento di una precisa consapevolezza dello stato dell’arte del settore, in particolare in riferimento ai processi attualmente utilizzati per l’industrializzazione in media-grande serie. Con l’obiettivo di sintetizzare i principali vantaggi delle tecnologie suddette e permettere la realizzazione di forme più complesse, si è proceduto all’analisi di fattibilità, attraverso uno studio funzionale e una prima progettazione di una tecnologia di produzione per nastratura automatizzata di componenti strutturali in materiale composito. Si è voluto quindi dimostrare la flessibilità e la consistenza del processo disegnando un telaio nastrato in carbonio, intercambiabile al telaio FSAE 2009 in tubolare d’acciaio (stessi punti di attacco motore, punti di attacco telaietto posteriore, attacchi sospensioni anteriori) e che garantisca un sostanziale vantaggio in termini di peso, a pari rigidezza torsionale. La caratterizzazione di tale telaio è stata eseguita mediante l'utilizzo del calcolo strutturale, validato da prove sperimentali.

Calibration of calculation models of wooden guardrails with Operational Modal Analysis

This study analyses the differences between two calculation models for guardrails on building sites that use wooden boards and tubular steel posts. Wood was considered an isotropic material in one model and an orthotropic material in a second model. The elastic constants of the wood were obtained with ultrasound. Frequencies and vibration modes were obtained for both models through linear analysis using the finite element method. The two models were experimentally calibrated through operational modal analysis. The results obtained show that for the three types of wood under analysis, the model which considered them as an orthotropic material fitted the experimental results better than the model which considered them as an isotropic material.

La silla de la discordia : la pequeña escala como campo de experimentación en la modernidad : Breuer, Mies y Stam

El siglo XIX fue un siglo dedicado a los grandes edificios públicos. Los teatros, las academias, los museos. Sin embargo la arquitectura durante el siglo XX se dedicará al estudio de la casa. Todos los usos y tipologías se verán fuertemente revisados pero el núcleo de todos los esfuerzos y verdadero inicio de la arquitectura moderna será la vivienda. A partir de ella todos los preceptos modernos se irán aplicando a los distintos programas. Nikolaus Pevsner señala a William Morris como el primer arquitecto moderno porque precisamente entendió que un arte verdaderamente social, en consonancia con su tiempo y la sociedad a la que sirve, ha de ocuparse de aquello que preocupe a la gente. Con la nueva situación de la vivienda en el centro de las motivaciones disciplinares el mueble adopta un nuevo protagonismo. En un momento avanzado de su carrera Marcel Breuer observa entre curioso e irónico cómo el mueble moderno había sido promocionado paradójicamente no por los diseñadores de muebles sino por los arquitectos1. La respuesta la da Le Corbusier en una de sus conferencias de 1931 recogida en Precisiones 2 cuando señala la reformulación del mobiliario como el "nudo gordiano" de cuya resolución pendía la renovación de la planta moderna. El Movimiento Moderno se había visto obligado a atacar este tema para poder avanzar en sus propuestas domésticas. El Movimiento Moderno se propuso solucionar los problemas de la vivienda y de una Europa en reconstrucción pero se exigía además ser capaz de aportar una visión propositiva de la vida moderna. No se trataba únicamente de resolver los problemas ya existentes sino que además había la necesidad autoimpuesta de anticipar la domesticidad del futuro. Para ello sus viviendas al completo, mueble e inmueble, debían de presentarse bajo esa nueva imagen. El manifiesto fundacional de la Deustcher Werkbund extendía el radio de acción del nuevo arquitecto desde la construcción de las ciudades a los cojines del sofá. Este mobiliario tenía la compleja misión de condensar sintéticamente todos esos ideales que la modernidad había traído consigo: abstracción, higiene, fascinación maquínica, confianza positivista en la ciencia o la expresión material optimizada. Objetos de la vida moderna, en palabras de Le Corbusier, susceptibles de suscitar un estado de vida moderno. Pocas sillas en la historia del diseño habrán acarreado tanta polémica y tanta disputa por su autoría como la sillas voladas de tubo de acero en sus diferentes versiones. Para entenderlo situémonos en el año 1927 a las puertas de la exposición "Die Wohnung" ("La vivienda") organizada por los maestros de la Bauhaus y dirigida por Mies van der Rohe en la ladera Weissenhof de Stuttgart. Muchos nombres célebres de la arquitectura mostraron en esa ocasión su personal propuesta para la vivienda moderna y los objetos que la habitan. Entre ellos los muebles con tubo de acero fueron una presencia constante en la exposición pero hubo una pieza que destacó sobre todas las demás por su novedad y audacia. La pieza en cuestión era el modelo de silla volada, esto es, sin apoyos posteriores y cuya rigidez estaba conferida al esfuerzo solidario de la estructura continua de tubo de acero y que terminaría por convertirse en el cruce de caminos de tres figuras de la disciplina arquitectónica: Marcel Breuer, Mies van der Rohe y Mart Stam. Cada uno de ellos desarrolló su propio modelo de silla volada en sus versiones MR por parte de Mies, L&C Arnold de Stam y el posterior modelo BR 33 de Marcel Breuer. Los tres, en algún momento de su vida reclamaron de uno u otro modo su autoría como objetos que les pertenecían intelectualmente. Estas sillas se convirtieron en la expresión máxima de uno de los ansiados anhelos de la modernidad, la propia materialidad del acero, en su versión optimizada, era la que había derivado en una forma completamente nueva de un objeto cotidiano y cuyo tipo estaba ya totalmente asumido. Los nuevos materiales y las nuevas formas de hacer habían irrumpido hasta en los utensilios domésticos, y habían sido capaces de reformularlos. El punto de partida para esta investigación es precisamente esa coincidencia de tres figuras de la arquitectura moderna, los tres de formación artesanal, en un mismo modelo de silla y en una misma fecha. Tres arquitectos que se habían encargado de asegurar que el movimiento moderno no reconocía problemas formales sino solamente de construcción, iban a coincidir en el mismo tiempo y lugar, precisamente en una misma forma, como si tal coincidencia hubiera sido producto de una voluntad de época. Sin embargo el interés de este estudio no radica en una indagación sobre la autoría sino sobre cómo un mismo objeto resulta ser propositivo e interesante en campos muy diversos y la forma en que cada uno lo hace suyo incorporándolo a su propia investigación proyectual. La silla, más allá de ser un objeto de diseño exclusivamente, trasciende su propia escala para situarse inmersa en un proceso de búsqueda y exploración a nivel conceptual, formal, constructivo y estructural en la arquitectura cada uno de ellos. En un momento en que el oficio del arquitecto está siendo intensamente redefinido considero especialmente pertinente esta investigación, que en definitiva versa sobre la forma distintiva en que el pensamiento arquitectónico es capaz de proyectarse sobre cualquier disciplina para reformularla. ABSTRACT The nineteenth century was a century dedicated to the great public buildings; theaters, schools or museums. However the architecture in the twentieth century was devoted to the study of housing. All uses and typologies were heavily revised but the focus of all efforts and true beginning of modern architecture was housing. From these beginnings all modern precepts were applied to the various programs. Nikolaus Pevsner points to William Morris as the first modern architect precisely because he understood that a truly social art in line with its time and the society it serves must deal with social concerns at that time. With the new housing situation at the center of disciplinary concerns furniture took on a new prominence. At an advanced stage of his career Marcel Breuer observed partly with curiosity, partly with irony how modern furniture had been promoted not by furniture designers but by architects. The answer is given by Le Corbusier in one of his lectures of 1931 collected in Precisions when he pointed the reformulation of furniture as the "Gordian knot" for the renewal of modern plan resolution. Modernism had been forced to confront this issue in order to advance their domestic approaches. Modernism not only put forward a solution to the problems of housing and a Europe under reconstruction but is also needed to be able to contribute to an exciting vision of modern life. Not only did solve existing problems but also it had the self-imposed necessity of anticipating future domesticity and to do their houses full, movable and immovable, they should be submitted under this new image. The founding manifesto of the Deutsche Werkbund extended the scope of the new architect from building cities to the couch cushions. This furniture had the complex mission of synthetically condensing all the ideals of modernity had brought with it: abstraction, hygiene, mechanization, positivist confidence in science or material expression. Objects of modern life, in words of Le Corbusier, were likely to give rise a state of modern life. Few chairs in design history have resulted in so much controversy and so much dispute over their invention as the various versions of cantilevered tubular steel chairs. To understand this let us place ourselves in 1927 at the gates of the exhibition "Die Wohnung" ("Housing") organized by the teachers of the Bauhaus and directed by Mies van der Rohe in Stuttgart Weissenhoflung. Many famous names in architecture at that time showed their personal proposals for modern housing and the objects that inhabit them. Amongst these objects, the steel tube furniture was a constant presence at the exhibition but there was a piece so audacious that it stood out from all the others. This piece in question was the cantilever model chair, that is, which had no further rear support and whose rigidity was attributed to the solidity of its continues structure of steel tube. This piece would eventually become the crossroads of three very different personalities: Mart Stam, Marcel Breuer and Mies van der Rohe. Each of them developed their own model of cantilevered chair in different versions; The MR model developed by Mies van der Rohe, the L&C by Arnold Stam and a later model BR 33 by Marcel Breuer, and the three, at some point in their lives demanded the authorship of its invention as objects that belonged to them intellectually. These chairs epitomized one of the coveted objects of modernity, steel material in its optimized version, was what had led to a completely new form of an everyday object whose this type was fully adopted on board in design. New materials and production methods had burst into world of household objects, and had been able to reformulate their design. The bold design then became a dark object of controversy. The starting point for this doctoral thesis is the concurrent invention of the same model of chair by three different figures of modern architecture. These three architects, who were responsible for ensuring that the modern movement considered construction rather than form as the main design consideration, were working in the same place and at the same point in time. It was almost as if these three architects were shaped by the culture of the time (Zeitgeist). However the focus of this study lies not in an investigation of responsibility of ownership but in the investigation fo how the same object can turn out to be purposeful and interesting in many different fields and the way in which each researcher makes it his own by developing his own project research. 1927, the year of their meeting, was a initiatory year in the career of our players. The chair, beyond being only a design object transcended its own scale and became immersed in a process of research and development on a conceptual, formal, structural and constructive level in the architectural approach of each of the architects. At a time when the role of the architect is being redefined intensely I consider this research, which ultimately concerns the distinctive way the architectural thought can be projected onto and reformulate any discipline, to be particularly relevant.

Design of concrete-filled steel tubular columns under axial loading according to NBR 8800:2008 and Eurocode 4:2004: tests results and comparisons

In this paper results of tests on 32 concrete-filled steel tubular columns under axial load are reported. The test parameters were the concrete compressive strength, the column slenderness (L/D) and the wall thickness (t). The test results were compared with predictions from the codes NBR 8800:2008 and EN 1994-1-1:2004 (EC4). The columns were 3, 5, 7 and 10 length to diameter ratios (L/D) and were tested with 30MPa, 60MPa, 80MPa and 100MPa concrete compressive strengths. The results of ultimate strength predicted by codes showed good agreement with experimental results. The results of NBR 8800 code were the most conservative and the EC4 showed the best results, in mean, but it was not conservative for usual concrete-filled short columns.

Structural capacity of steel tubular cast-in-place piling

Steel tubular cast-in-place pilings are used throughout the country for many different project types. These piles are a closed-end pipe with varying wall thicknesses and outer diameters, that are driven to depth and then the core is filled with concrete. These piles are typically used for smaller bridges, or secondary structures. Mostly the piling is designed based on a resistance based method which is a function of the soil properties of which the pile is driven through, however there is a structural capacity of these members that is considered to be the upper bound on the loading of the member. This structural capacity is given by the AASHTO LRFD (2010), with two methods. These two methods are based on a composite or non-composite section. Many state agencies and corporations use the non-composite equation because it is requires much less computation and is known to be conservative. However with the trends of the time, more and more structural elements are being investigated to determine ways to better understand the mechanics of the members, which could lead to more efficient and safer designs. In this project, a set of these piling are investigated. The way the cross section reacts to several different loading conditions, along with a more detailed observation of the material properties is considered as part of this research. The evaluation consisted of testing stub sections of pile with varying sizes (10-¾”, 12-¾”), wall thicknesses (0.375”, 0.5”), and testing methods (whole compression, composite compression, push through, core sampling). These stub sections were chosen as they would represent a similar bracing length to many different soils. In addition, a finite element model was developed using ANSYS to predict the strains from the testing of the pile cross sections. This model was able to simulate the strains from most of the loading conditions and sizes that were tested. The bond between the steel shell and the concrete core, along with the concrete strength through the depth of the cross section were some of the material properties of these sections that were investigated.

Steel tubular products in general use as water-well pipe / c by H.L. Conklin.

Mode of access: Internet.

Projeto de uma ponte atirantada rodoferroviária sobre o rio Lima, Viana do Castelo

Trabalho académico com o objetivo do autor desenvolver um estudo prévio e um projeto de uma travessia sobre o rio Lima, na cidade de Viana do Castelo constituída por uma ponte de tirantes rodoferroviária. O projeto académico visa, também, desenvolver e compreender: os conceitos básicos, as metodologias de conceção, e o funcionamento de estruturas desse género. O motivo principal da escolha do tema é a necessidade de uma alternativa à ponte Eiffel em Viana do Castelo, e juntando o facto de em Portugal não existir nenhuma obra de arte de tirantes rodoferroviária até ao presente, seria interessante estudar e projetar uma estrutura rodoferroviária de tirantes. Das diversas possibilidades de sistemas estruturais estudados, adotou-se uma ponte que acomodará 4 vias rodoviárias e 2 vias ferroviárias, com um desenvolvimento total de 660 metros, constituída por dois vãos laterais com 165 metros cada um, e com um vão central de 330 metros. A obra de arte será em semi-leque com dois planos de tirantes, ancorados a duas torres de betão em Y invertido de altura aproximadamente de 110 metros. O tabuleiro será duplo misto aço-betão, constituído por duas vigas trianguladas do tipo Warren, e por carlingas, afastadas entre si de 15 metros com secções tubulares metálicas de espessura variável. As carlingas ao nível superior suportam a laje de betão, que constitui a rodovia, e inferiormente, suportam outra laje de betão para a parte ferroviária. O trabalho inicia-se com o enquadramento conceptual geral da envolvente da obra de arte, seguidamente com apresentação da evolução histórica ao longo do tempo das pontes de tirantes, e à apresentação de algumas pontes rodoferroviárias de tirantes. É realizada uma análise preliminar, onde se estudam as restrições, as condicionantes, o local de implantação, e o sistema da configuração geométrica a adotar na conceção estrutural. São descritos todos os tipos de materiais, equipamentos a utilizar, bem como as suas características mecânicas necessárias para o cálculo estrutural. A quantificação das ações e das combinações de cálculo efetuaram-se de acordo com as normas em vigor nacionais e europeias, designadamente os Eurocódigos das várias especialidades e o Regulamento de Segurança e Ações para Estruturas de Edifícios e Pontes. Efetuou-se um pré-dimensionamento e uma otimização de vários sistemas estruturais possíveis de todos os elementos estruturais, tendo em conta variáveis de estudo como a economia e a resistência estrutural das secções, por forma a chegar à solução final. A estrutura foi discretizada e analisada num modelo estático tridimensional num programa de cálculo automático. A análise de resultados foi efetuada longitudinalmente para a verificação dos Estados Limites Últimos e Estados Limites de Utilização dos elementos estruturais que constituem a ponte. Foi ainda efetuada uma estimativa orçamental da ponte no rio Lima na cidade de Viana do Castelo.

Efeito dos parâmetros de pulso sobre as características geométricas e desempenho da soldagem com arame tubular autoprotegido e corrente pulsada

Pós-graduação em Engenharia Mecânica - FEB

Efeitos da vibração simultânea nas propriedades mecânicas de juntas de aço ASTM A131 soldadas pelo processo arame tubular (FCAW)

Pós-graduação em Engenharia Mecânica - FEG

Caracterização microestrutural de uma estrutura tubular aeronáutica submetida a sucessivos reparos de solda TIG

This work examines the possible effects of successive repair procedures on the microstructure of welded steel SAE 4130 by TIG welding process. Discussions and results were made about the metallographic analysis , non-metallic inclusions and microhardness tests , which were conducted on samples taken from the cradle engine component after the end of its life , a model airplane T-27 Tucano , made by EMBRAER and belonging were performed FAB . The choice of such component is due to the fact that this is critical to flight safety since it provides support for the aircraft engine . Thus regions of the weld metal , base metal and heat affected , with samples of the original weld bead , free of weld bead and also with four rework procedures for TIG welding zone were analyzed . It was found that after the fourth rework there is an increase in the amount of martensite , which may weaken the material with respect to resistance to fatigue. It was also found that the regions of the heat affected zone and weld metal have higher microhardness values when compared to those found in the base metal due to favoring the formation of ferritic and tempered martensite microstructures . Moreover, a welding process promotes a region with less non-metallic inclusions than metal base , which also explains the difference in the results obtained