Estimation model of mechanical properties from the compressive strength values

Anderson Renato Vobornik Wolenski,André Luís Christoforo,Francisco Antonio Rocco Lahr,Rodrigo Guerra Peixoto,João Paulo Boff Almeida

doi:10.4067/s0718-221x2020005000407

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 pro-poses 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

Highlights

Considering the importance of mechanical properties in the design of such timber structures as bridges, sheds and houses (Ruelle et al 2011, Dadzie and Amoah 2015), it is of great relevance to evaluate the normative documents which aim to estimate the strength properties of species used in construction
36 tropical hardwood species were experimentally classified employing the procedures of the Brazilian standard for timber structures
The evaluated species demonstrated a potential for application in civil construction and the results have shown that the Brazilian hardwoods tested here are disposed among all the strength classes with the range between 20 MPa and 90 MPa of compressive strength in the direction parallel to the grain

Summary

Introduction

Considering the importance of mechanical properties in the design of such timber structures as bridges, sheds and houses (Ruelle et al 2011, Dadzie and Amoah 2015), it is of great relevance to evaluate the normative documents which aim to estimate the strength properties of species used in construction. In Brazil, the timber structures have an elevated applicability potential due to a vast number of wood species existing in the Amazonian rainforest. According to Steege et al (2016), by 2015 there were already discovered more than 10000 wood species. This number induces development of new research aiming at characterization of species that can potentially substitute those that already are commonly used in construction.

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Results

Conclusion