Abstract
Wood strength values are calculated based on the characteristic value, which corresponds to the 5 % percentile of a given probability distribution model. For a few number of samples (12 samples), the Brazilian standard establishes an estimator of the characteristic compressive strength parallel to grain of the wood, which may provide a different result when compared with the characteristic value coming from a suitable probability distribution model. Considering the strength results in the parallel compression to the grain of 45 wood species of the hardwood group, Normal, LogNormal, Weibull and Exponential probability distribution models were used for each specie with the purpose of determining the one with the highest adhesion. Calculated the char-acteristic values by the best probability model distribution, an analysis of variance (ANOVA) was performed in the estimation of the characteristic value of compressive strength, making it possible to identify the most significant terms of the models as well as the quality of the adjustment obtained on such models. The proposed regression model (R2 adj= 96,56 %) proved to be equivalent to the empirical model of the Brazilian standard. The model proposed here only depends on the mean and the lowest value obtained from the compressive strength in the parallel direction to the grain.
Highlights
IntroductionThe wood, a natural and renewable source material, presents a good relation between mechanical strength and density (Arruda et al 2015, Baar et al 2015, Cavalheiro et al 2016), which makes it suitable for use in construction (Andrade Jr. et al 2014, Chen and Guo 2017, Lahr et al 2017).Brazil is a country with enormous potential for timber applications, since the availability of wood species from the Amazon Forest is the order of 11194 wood species, cataloged between the years 1707 and 2015 (Steege et al 2016) these conditions motivated the development of new researches with the purpose of characterizing new species to replace those commonly used in civil construction (Ferro et al 2015, Freitas et al 2016, Almeida et al 2016, Christoforo et al 2017).Maderas
The confidence interval (CI) of the mean for fc0,k calculated by the probability distribution models resulted in CI = (45,88; 55,56 MPa), 31,77 % coefficient of variation obtained
From 45 wood species evaluated by the probability distribution models in fc0,k, 40 % (18/45) of the species were better represented by the LogNormal model, 17,78 % (8/45) were better adjusted by the Normal distribution model and 42,22 % (19/45) by the Weibull model, and it should be noted that the Exponential model did not provide a significant adjustment for fc0,k in any of the evaluated species
Summary
The wood, a natural and renewable source material, presents a good relation between mechanical strength and density (Arruda et al 2015, Baar et al 2015, Cavalheiro et al 2016), which makes it suitable for use in construction (Andrade Jr. et al 2014, Chen and Guo 2017, Lahr et al 2017).Brazil is a country with enormous potential for timber applications, since the availability of wood species from the Amazon Forest is the order of 11194 wood species, cataloged between the years 1707 and 2015 (Steege et al 2016) these conditions motivated the development of new researches with the purpose of characterizing new species to replace those commonly used in civil construction (Ferro et al 2015, Freitas et al 2016, Almeida et al 2016, Christoforo et al 2017).Maderas. For reasons of structural design safety, the values of strength to the mechanical stresses of the wood are obtained based on the characteristic value (and not on the mean value), which corresponds to the 5 % percentile of the respective probability distribution. According to the probabilistic method of the Brazilian standard ABNT NBR 7190 (1997), a normal distribution is assumed of the strength values. Such hypothesis is based on the consideration of large number of samples (30 or more test specimens) together with a value limit of 18 % of the coefficient of variation. Given the average value of the strength ( f ) and its standard deviation (sd), the characteristic value (fwk) of the property is determined using Equation 1
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