In an effort to achieve lighter and more economical space structures, a new patented steel composite member has been suggested and used in the construction of some steel roof structures. This special element has a sandwich construction composed of some strips of steel plates placed longitudinally along a helical wire core. The function of the helical core is to transfer the shear between the flange plates and increase the sectional inertia of the resulting composite member by keeping the flange plates at a desired distance from each other. Because of the lack of research, design engineers usually treat such elements as a solid member as if it has a full shear transfer between the flanges. However, a detailed analysis shows that this is not a valid assumption and leads to very unsafe results. In this context, the purpose of this study is to investigate the behavior of such members under axial compression and determine their effective sectional flexural rigidity by taking into account the shear deformations. This study applies an analytical investigation to a specific form of such elements with four flange plates placed symmetrically around a helical wire core. Five independent parameters of such a member are selected for this purpose. These are the spiral core and core wire diameters, the pitch of the spiral core, and the flange plate dimensions. Elements with varying combinations of the selected parameters are first analyzed in detail by finite element method, and some design charts are generated for the determination of the effective sectional properties to be used in the structural analysis and the buckling loads. For this purpose, an alternative closed-form approximate analytical solution is also suggested.

[pt] Os sistemas de cobertura constituem uma parcela considerável dos custos finais de galpões de grandes dimensões. Os carregamentos desse sistema são transferidos para os pilares a partir dos vigamentos principais. Dúvidas sobre qual é a melhor solução para o dimensionamento do vigamento principal podem surgir devido aos grandes vãos que essas estruturas devem cumprir. Esta dissertação apresenta um estudo das configurações estruturais e uso de diferentes materiais para o projeto, fabricação e montagem de coberturas de galpões de grandes dimensões. Foram desenvolvidos diversos projetos de uma estrutura modelo onde se variou o tipo de perfil das cordas, o comprimento dos vãos, a geometria da seção transversal da treliça e a inclinação das diagonais. A partir dos resultados obtidos, realizou-se uma análise paramétrica buscando-se a solução que apresenta o menor peso estrutural dos vigamentos principais. A grande vantagem da utilização de treliças multiplanares é o bom comportamento fora do plano que esse tipo de estrutura oferece, podendo reduzir custos com travamentos e elementos secundários. Também foi realizado um estudo determinístico para dar apoio às decisões na escolha da melhor solução para os diversos tipos de galpões de grandes dimensões estudados. Os resultados preliminares obtidos indicam que a solução de cordas tubulares mistas, em partes selecionadas da estrutura, representa uma das soluções mais competitivas para este tipo de estrutura. / [en] Roofing systems constitute a considerable part of the final costs of large single-storey buildings. The loads of this system are transferred to the columns from the girders. During the design process may be raised the question of what may be the best solutions for the roof supporting girders, mainly due to the large spans required. This dissertation presents a study of the structural configurations and the use of different materials for the design, manufacture and assembly of roofs of large single-storey buildings. Several designs of a model structure were developed where the type of profile of the main chords, the length of the spans, the geometry of the cross-section of the truss and the angulation of diagonals were varied. Based on the obtained results, a parametric analysis was performed focused on solutions presenting the lower structural weight of the girders. The great advantage of using multiplanar trusses is the good behavior out of plane that this type of structure offers, which can reduce costs with bracing and secondary elements. A deterministic study was also carried out in order to support decisions in choosing the best solution for the various types of large single-storey buildings studied. The preliminary results obtained indicate that the solution of concrete filled steel tubular chords in selected parts of the structure represents one of the most competitive solutions for this type of construction.