Abstract Circular hollow sections are usually used in long-span roof truss systems. One of the typology for connecting elements in such structures involves the flattening of bar ends. This article presents the numerical analysis of a plane truss composed of circular hollow sections, in which diagonal bars have flattened ends. In this sense, a new flattening typology called stiffened flattening is proposed, characterized by a non-flat geometry, with the creation of stiffeners in the lateral edges of the diagonal flattened ends. The diagonal connecting system with the chord members uses connecting plates. The plates are welded to the chords and the diagonals are connected to latter through a single bolt. The numerical analysis using finite elements method was developed in two stages through ANSYS software with the Parametric Design Language (APDL), in which parameters such as geometry, materials, element types, boundary conditions and loads are specified. A non-linear analysis was performed using shell elements on the chords, diagonals, plates and welds, and contact elements between the diagonals with stiffened flattened ends and the connecting plates. Initially, a numerical study of the connecting node and the stiffened flattened end was performed, and the results directed the modeling of the plane truss. The numerical results were calibrated with the experimental truss results in full scale. The numerical result of the plane truss was also compared to a theoretical study, considering the axial load eccentricity applied in the diagonal with stiffened flattened ends. The study was based on the consideration of combined effects of axial force and bending moment provided by the Brazilian standard ABNT NBR 8800:2008. The final results indicate that the numerical model proposed is efficient and has good correlation with the experimental and theoretical results.

Abstract The circular hollow sections (CHS) are being widely employed in steel structures around the world, increasing the development of new researches. This article proposes an innovative connection model for circular hollow sections that facilitates and reduces the assembly cost of hollow section structures. The proposed connection is a tube sleeve, used to splice two tubes, composed of an inner tube with a diameter smaller than the connecting tubes, which is connected to the outer tubes by bolts passing through both tubes. This connection can be a cheaper and easier alternative to flange connections, which are widely used in large span tubular trusses. The connection was tested in laboratory under tension loading. The tests made it possible to identify the influence of stress distribution on tubes and the need for the use of a shear lag coefficient. The results of the ultimate load capacity demonstrated the viability of the tube sleeve connection use.

A ventilação natural no interior das edificações proporciona condições favoráveis de conforto térmico aos ocupantes, além da melhoria da qualidade do ar interno. A eficiência da ventilação natural numa edificação está associada ao número, posição, tipo e tamanho das aberturas existentes para a passagem de ar e também à ação combinada das forças do vento e das diferenças de temperatura. No caso da construção de galpões industriais e edificações comerciais, é usual construir aberturas nas coberturas (lanternins), além daquelas aberturas nas fachadas, para se obter iluminação natural e também melhorar a ventilação natural. Nesse trabalho, estuda-se a ventilação natural em galpões utilizando lanternins. Apresenta-se uma modelagem matemática, associada com o conceito do índice de ventilação natural, para o cálculo da vazão de ar necessária para uma ventilação natural adequada em edificações e também para o cálculo das áreas das aberturas necessárias para suportar uma dada vazão. Ainda por meio de uma abordagem numérica, analisam-se o fluxo de ar no interior do galpão e o perfil da temperatura interna resultantes da simulação. Os resultados obtidos levaram em consideração o grau de conforto térmico necessário no interior do galpão e comprovam a abertura necessária do lanternim calculada para se alcançarem as condições internas de conforto.

Natural ventilation inside constructions allows both favorable conditions for thermal comfort to the occupants and quality improvement of the internal air. The efficiency of natural ventilation in a building is associated to the number, position, type and size of the existing openings for the passage of air. It is also associated to the combined action of wind forces and temperature differences. In the case of building industrial hangars and commercial facilities, it is usual to construct openings in the roofs (skylight with an entrance and an exit), besides openings in the facades. This work focuses on the natural ventilation in hangars through the use of skylights in the roofs. It presents a mathematical modeling, associated with the concept of the natural ventilation index. A numerical simulation was used to analyse both the air flow inside the hangar and the internal temperature profile. The airflow and the temperature profile were obtained by simulation. The obtained results took into account the degree of necessary thermal comfort inside the hangar. The results present the necessary size of the opening to obtain adequate internal conditions of comfort.