Avaliação experimental de vigas com emendas de topo coladas com cobrejuntas de madeira de eucalipto

• Autor(a) principal: Lobão, Moisés Silveira
• Data de Publicação: 2002
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/3215
• topic: Madeira laminada; Resistência ao cisalhamento; Vigas; Deformações e tensões; Flexão; Engenharia civil; Estruturas de madeira; Juntas; Eucalipto; Laminated wood; Shear strength; Beams; Strain and stress; Flexure; Civil engineering; Wood structures; Joints; Eucalyptus; CNPQ::CIENCIAS AGRARIAS::RECURSOS FLORESTAIS E ENGENHARIA FLORESTAL::TECNOLOGIA E UTILIZACAO DE PRODUTOS FLORESTAIS

The objective of the present work was the construction, testing and evaluation of the behavior of wooden beams made of eucalyptus boards with mid-span end-grain joints. The adhesive utilized was a resorcinol-formaldehyde glue and the joints were covered by side members of the same species of wood. Strength and stiffness of these beams were compared with the results solid beams. Eucalyptus lumber was purchased in the local market for the purpose. It was found, when the shipment arrived, that the whole lot could be segregated into two sub-lots, one of higher specific gravity timber, another of less dense wood. Wood properties were determined for these two subsamples, according to the recommendations of the Brazilian Association of Testing Standards, NBR 7190/97. It was found that the specific gravity (weight and volume at 12% moisture content) of the less dense lumber was 575 kg/m3 while the denser timber reached 880 kg/m3. The average value of the whole lot was 721 kg/m3. It was concluded that the shipment included at least two species; testing for mechanical properties also yielded quite different results. Glue-bond quality was also determined according to NBR 7190/97 in samples made to represent the two different densities; the shear planes, however, included two possibilities: the two pieces that formed the block had their fibers both parallel or one of the parts had their fibers perpendicular to those of the other part. Shear strength was determined by compression using these blocks; the percentage of wood failure was also measured. It was found that the low density wood glued well, because the average shear strength of the blocks with fibers of the parts parallel to the direction of the force did not differ from the shear strength of solid wood. High density wood did not glue so well, as well as the samples made with fibers of the parts parallel/perpendicular to the shearing force. Prototype beams were then built to find the best size of the side members that symmetrically covered the joints. These beams had a length of 170 cm, were 3 cm wide and 10 cm deep and were tested to failure using a center load on a 160-cm span. It was found that the1.5 cm thick side members should cover at least 25% of the two sides of the beam to give the same results of strength and stiffness of solid 170 cm long beams. Larger beams were then built and tested. They had a length of 420 cm and were 20 cm deep and 6 cm wide. Some, the controls, were built of a single piece of lumber; other were made of 210 cm long boards, joined at mid-section by 100 cm long, 3 cm thick side members. These glued beams proved, after tested, to be of similar strength as the solid ones and were, in fact, stiffer than the controls, due to the larger moment of inertia at their central portion.