INFLUENCE OF THE ANGLE BETWEEN APPLIED FORCE AND WOOD GRAIN DIRECTION ON SHEAR STRENGTH
DOI:
https://doi.org/10.5902/1980509816610Keywords:
shear strength, characteristic strength, fibers inclination.Abstract
http://dx.doi.org/10.5902/1980509816610
Wood is an anisotropic material and its resistance characteristics vary with the angle between the effort and the fiber direction (a). The Brazilian Code NBR 7190 – Design of Wooden Structures, foresees the strength correction to the normal stress, whenever a > 6o, and it recommends to apply Hankinson's expression to design values. However, this referred code is omitted about this correction to the tangential stress. Besides, there is not experimental confirmation about the validity of using this expression on design values, originating from characteristic values. The objectives of this work were: to search in the bibliography other used expressions; to verify the validity of these expressions, to represent the variation of the shear strength, with the a angle; and, to verify the validity of application of these expressions in characteristic values. For this, a sample formed by twelve boards was used. From each board, specimens to shear tests were retired, with different fibers inclinations, which were tested in agreement with current NBR 7190, supplying the shear strength, for different a values. Four models (Hankinson, Sin, Karlsen and Keylwerth) were evaluated, using the pairing and deviation tests. The model that best represented the phenomenon, in both cases, was Keylwerth’s.
Downloads
References
ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 7190 - Projeto de estruturas de Madeira. Rio de Janeiro: ABNT, 1997. 107 p
KARLSEN, G. G. et al. Wooden Structures. Moscow, Russia: Mir Publishers, 1967. 638 p
KOLLMANN, F. F. P. E CÔTÉ JR., W. A. Principles of wood science and technology, vol. I Solid Wood. New York: Springer-Verlag, 1984, 502 p.
LOGSDON, N. B. Influência da umidade nas propriedades de resistência e rigidez da madeira. 1998. 174 f. Tese (Doutorado em Engenharia de Estruturas) – Escola de Engenharia de São Carlos – Universidade de São Paulo, São Carlos.
NICOLAS, A. N.; MASCIA, N. T.; TODESCHINI, R. Comparação entre o critério de Tsai-Wu e a fórmula de Hankinson na tração da madeira. Madeira: Arquitetura e Engenharia, São Carlos, ano 9, n. 23. p. 13-29. São Carlos. jul./dez. 2008.
PFEIL, W. Estruturas de madeira: dimensionamento segundo as normas brasileiras NB-11 e os modernos critérios das normas alemãs e americanas, Rio de Janeiro: Livros Técnicos e Científicos, 1978. 253 p
SZÜCS, C. A. Estudo do comportamento da madeira a esforços inclinados, In: ENCONTRO BRASILEIRO EM MADEIRAS E EM ESTRUTURAS DE MADEIRA, 4., 1992, São Carlos. Anais... Instituto Brasileiro das Madeiras e das Estruturas de Madeira: São Carlos, 1992. v. 2, p. 53-60.
TSAI, S. W.; WU, E. M. A general theory of strength for anisotropic materials. Journal of Composite Materials, n. 1, v. 5, p. 58-80. 1971.
