Estimation of the characteristic value of wood strength

Abstract

For safety reasons, wood strength values, essential for structural dimensioning, are calculated based on the characteristic value, which corresponds to the 5% percentile of a given probability distribution model. For small samples, the Brazilian normative document ABNT NBR 7190 establishes an estimator of the characteristic wood strength, which can provide a significantly different result from the characteristic value coming from a suitable model of probability distribution. The main objective of this study was to evaluate the best probability distribution model (normal, lognormal, Weibull, and exponential) and the subsequent calculation of the characteristic value indicated by ABNT NBR 7190 (1997), allowing to evaluate its accuracy, being also investigated two relationships between characteristic values of the simplified characterization condition for woods of species already known. The best adhesion model was the normal model, which resulted in values statistically equivalent to the characteristic values according to ABNT NBR 7190 (1997). Among the evaluated relationships, the obtained results were significantly higher (up to 92%) when compared to those estimated by ABNT NBR 7190 (1997).