Procedure for Estimate Tensile Strength Parallel to the Grain of Tropical Wood Species

Wood is a renewable resource, abundant in Brazil, and presents a high relationship between
mechanical strength and density, which makes it suitable for use in building structures. In Brazil, the
determination of tensile strength parallel to the grain is performed following the disposed on Brazilian
Standard ABNT NBR 7190, using the ratio between maximum force and cross-section of the proof
test. This method does not take into account the wood anatomy and the fracture plan, which does not
happen equal along cross section, with the fracture occurring with a larger area. Considering this, an
alternative method to evaluate fractured cross section area and estimate tensile strength along the
grain. This method used based on least squares method to evaluate tensile strength of hardwood,
divided by strength classes. The areas of specimens before and after fracture were compared and
correlated. The results illustrated that fracture area was 2.14 times higher than the area of not
fractured specimens. Then, the tensile strength values calculated based on intact specimen were, on
average, 47% lower to the values using the fractured cross-section area, leading to underestimate
tensile strength.