Analysis of a standardized parameter for the design of wooden structures considering structural reliability

Abstract

Reliability is related to the degree of reliability of a system, which must be established in the design, which should predict and specify itsoperating conditions. Annex E of standard NBR 7190:1997 for wooden structure projects presents results from a wide sampling of different dicotyledonous and coniferous species, with great variation in the number of specimens, fixing a coefficient of variation (CV) for normal and shear strength equal to 18% and 28%, respectively. This study evaluated, by using a probabilistic approach, the frequency distribution of samples of compressive strength parallel to the grain presented in the standard, seeking to specify the reliability index established. The results indicate that the data proposed may not be normally distributed, leading to distortions in the obtention of the characteristic strength. The adoption of a single coefficient of variation for the coniferous and dicotyledonous species is not ratified in the analysis of the data and, when considering the homogenisation of classes, different coefficients of variation are also generated. Regarding the proposed revision of NBR 7190, it is concluded that the inclusion of one more resistance class (D50) improves the distribution of the samples, however, the suppression of Annex E hinders the categorisation of classes by species.

Keywords:
Wood; Reliability; Strength classes; Sampling distribution; Structural safety