Abstract

DAVALOS-SOTELO, Raymundo  and  ORDONEZ CANDELARIA, Víctor Rubén. Effect of knots on the bending strength of pine wood for structural use. Rev. mex. de cienc. forestales [online]. 2011, vol.2, n.7, pp.43-56. ISSN 2007-1132.

In this study the effect of knots on the bending strength of pine wood for structural use is determined. Information is presented of a set of experimental data on the bending strength of Mexican pine wood and statistical analyses were made to quantitatively define this effect. One hundred and fifty specimens of 38 mm x 89 mm x 2400 mm in nominal size from the State of Mexico were tested in air-dry condition. The relationship of the knot area ratio (KAR) with strength (Modulus of rupture: MOR) was evaluated and multiple linear regression equations were generated, including the modulus of elasticity, in addition to these two variables. It is concluded that the effect of knots on bending strength of pine wood is substantial and that their presence causes a decrease of its values. The multiple linear regression equations calculated for various subsets of the sample data show low levels of R² for the relationship RAN-MOR but this increases significantly if Modulus of Elasticity (MOE) is included in the calculation. With this information, it could be possible to determine the acceptable values of KAR for different types of structural wood. These analyses could help to assess the efficiency of the current grading rules and to determine if they should be modified. To this end, apart from the knots, all apparent defects in commercial pine wood should be considered.

Keywords : Stress grading; design values; modulus of rupture; modulus of elasticity; knot area ratio; structural uses.

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