Wood, abundant in Brazil, is a renewable resource and has a high relationship between mechanical strength and density, making it ideal for use in building structures. In Brazil, in accordance with the Brazilian Standard ABNT NBR 7190, the calculation of the tensile strength parallel to the grain is carried out using the ratio between the maximum force and the cross-section of the proof measure. The wood anatomy and the fracture plan, which are not identical along the cross section, are not taken into account in this process, with the fracture occurring over a larger area. In view of this, an alternative method for measuring the area of the broken cross section and estimating the tensile strength along the grain is used. This approach was used to determine the tensile strength of hardwood, separated by strength classes, on the basis of the least square method. The pre- and post-fracture areas of specimens were compared and associated. The findings showed that the fracture area was 2.14 times greater than the area of the specimens that were not broken. Then, on average, the tensile strength values calculated on the basis of the intact sample were 47 percent lower than those calculated on the basis of the broken cross-section area, leading to an underestimation of tensile strength.
André Luis Christoforo
Department of Civil Engineering (DECiv), Federal University of São Carlos, São Carlos/SP, Brazil.
Vinicius Borges de Moura Aquino
Araguaia Engineering Institute, Federal University of Southern and Southeastern Pará (UNIFESSPA), Santana do Araguaia/PA, Brazil.
Tulio Hallak Panzera
Department of Mechanical Engineering, Federal University of São João del-Rei (UFSJ), São João del-Rei/MG, Brazil.
Francisco Antonio Rocco Lahr
Department of Structural Engineering, São Carlos School of Engineering of São Carlos, University of São Paulo (USP), São Carlos/SP, Brazil.
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