Estimation model of mechanical properties from the compressive strength values

Abstract

To ensure the safety of wooden structures, estimation of wood strength is based on the characteristic
strength values. The Brazilian standard (NBR, in Portuguese Norma Brasileira Regulamentadora) 7190 proposes
equations to estimate the strength properties with a simplified procedure, which allows obtaining the
characteristic values through relations that correlate different mechanical properties. Using these equations,
the values of tensile (ft0,k) and shear (fv0,k) strength can be calculated in a simplified way from the compressive
strength (fc0,k) values. In the present work, 36 tropical hardwood species were evaluated for tensile, shear and
compressive strength in the direction parallel to the grain, with a total of 1296 experimental measurements,
and the precision of the relations defined by the Brazilian standard was assessed using the analysis of variance
(ANOVA) method. Two-parameter regression models, based on linear, exponential, logarithmic and geometric
functions, were used as an alternative proposal for the estimation of the strength properties. The statistical
analysis validated the proposed relations, with the linear (ft0,k) and geometric (fv0,k) regression models being
the models of best fit, with the coefficients of determination (R2) equal to 63,02 % and 70,15 %, respectively.
In addition, new simplified equations were suggested. The least squares method was used to determine the
optimal coefficient (α) for validation of the Brazilian standard equations. The obtained coefficients validated
the tensile strength relationship (ft0,k = fc0,k / 0,77), but failed to validate the shear strength relationship (fv0,k =
0,12∙ fc0,k). In the latter case, the obtained values were significantly higher (up to 91 % higher) when compared
to those estimated by the Standard