Efeitos produzidos por variações bruscas em seção transversal de peças estruturais de madeira

Abstract

Often, timber beams are notched by many reasons: facilitate support, bring the top surface level with other beams, accommodate pipes, make connections between structural parts, and others. However, notches can cause a significant reduction in the load-carrying capacity of the beams, since the abrupt change in cross-section creates, besides the reduction of the cross-section, stress concentrations around the notch, especially in the corner. The intensity of these side effects depends on the size, geometry and position of notches in the beam. In order to correct these effects, several wood design standards provide special recommendations. The results of several numerical simulations of different cases of notched beams were presented in this work focusing in the analysis of stresses and displacements. It was also evaluated the effects produced by the notches in the beams, by comparison with those obtained by the classical equations of Strength of Materials. This allows proposing correction factors to adjust the notched effect. The numerical analysis was based on the finite element method applied to a beam, in which they have been considered in the three-dimensional shape by ANSYS® software, using the element SOLID45. Considering the numerical singularity at the corners of the notches, the submodeling technique associated with the plasticity of the material was used to achieve results convergence. It was also made a comparison between the correction factors obtained in this paper with those proposed by the analyzed standards for wooden structures. Among the analyzed standards, the Brazilian ABNT NBR 7190:1997 was the poorest in specifications and justifications, and it would be interesting that it restricts the execution of notches in the middle third of the span of the beam, which is a critical situation, and limit the dimensions of the notches in the outer thirds of the span similarly to American and Chilean standards.