Estudo numérico experimental de treliças espaciais feitas com tubos de aço com ponta amassada e espaçadores de madeira para corrigir as excentricidades nos nós de ligação

Abstract

Space trusses made of tubes with flattened ends connected with a trespassing bolt (typical connection) are widely used due to its easy construction and economy with respect to patented connections. However, the typical connection is weak due to the eccentricity and reduced momentum of inertia that exists at the nodes due to the flattening process. In previous studies, it was observed that when correcting the eccentricity generated by converging tubes at the same node, using steel spacers, the truss can support more load considerably. However, the use of such spacers made of steel increased the cost of production and generated additional dead load. Thus, the objective of the present research is to replace the steel spacers for spacers made of wood, which are more economical and lighter. To assess the improvement in the bearing capacity of the truss, this work applied a numerical and experimental approach to exam the feasibility of using wood spacer. In the numerical study, a tubular tetrahedral spatial lattice with square base 2m by 2m and 0.7m height was used. In the numerical analysis the commercial Finite Element software, ANSYS Workbench 14.5 was employed. The numerical analyses considered the detailed geometry of the truss as well as the non-linear behavior of the material and geometry trying to model the truss as close to reality as possible. In the experimental study, three trusses with typical connections and "Maçaranduba" wooden spacers were tested. In these tests, it was observed that the wood spacers withstood the loads. Moreover, the bearing capacity of the truss was very similar to bearing capacity of the previous trusses using steel spacers. The types of deformation (buckling and local deformations) shown in the numerical model and in the experimental test were very similar. This similarity in the results highlights that the numerical model adequately predicted the collapse and deformed shape of the trusses observed in the lab tests. Therefore, in conclusion: the results show that the use of wood spacers is feasible and an alternative to replace steel spacers in trusses with less weight and cost.

Experimental Analysis of Space Trusses Using Spacers of Concrete with Steel Fiber and Sisal Fiber

“…Figure 6a shows the details of this collapse due to welding failures. In Brazil, accidents also happened in 3D structures [9,17,24,[54][55][56][57][58][59]. One major accident was the roof of the Manaus Convention Center in April 1994.…”

“…MERO connection was widely used commercially and was developed in Germany by Dr. Ing. Max Mengeringhausen and Rohbauwwise [1,5,[11][12][13][14][15][16][17][18] (see Figure 1). After the invention of the MERO connection, several other systems were patented with the same principle: Steel ball, hexagonal screw, connection sleeve, and hollow section bar.…”

Análise experimental de treliça tridimensional com correção da excentricidade na ligação estampada usando espaçadores de aço e com polímero reforçado com fibra de sisal

“…Conexão Octatube Conexão Vestrut Conexão Axis Figura 2-Ligações de treliças espaciais com patentes (Souza, 2003) e (Casanova, 2015) 2 Colapso de treliça tridimensional e nova proposta de solução O objetivo deste artigo está relacionado com o fato das treliças tridimensionais apresentarem instabilidades locais (Hill, Blandford e Wang, 1989), especificamente nas ligações do tipo estampadas, que apresentam rotações locais quando solicitadas, ocasionando colapso da ligação (Freitas, 2008), sem o aproveitamento da capacidade resistente das barras (Souza, 2003). Esse problema é explicado pelas mudanças geométricas geradas no modelo (Bezerra et al, 2009), devido à estampagem das barras, ocasionando o surgimento de excentricidade nas ligações (Gioncu, 1985), (Chan e Cho, 2005) e (Freitas et al, 2014) e (Silva et al, 2018).…”

“…De forma semelhante, no Brasil diversos acidentes também aconteceram devido ao colapso de estruturas tridimensionais (Sampaio, 2004), como por exemplo a cobertura do Centro de Convenções de Manaus apresentado na Figura 3b e 3c (Souza, 2003), (Freitas, 2008) e (Casanova, 2015), a estrutura pesava mais de cem toneladas que desabou em 19 de abril, de 1994 deixando 25 pessoas feridas. No momento da queda, 900 alunos estudavam em 18 salas que funcionava embaixo das arquibancadas do Sambódromo (Nogueira, Varellada, 1994).…”