Determination method of characteristic strength for structural wood materials based on normal distribution and random sampling.

Characteristic strength is a key mechanical property index for structural wood materials used in building structures, which should be determined according to requirements of confidence level and number of specimens contained in sample. Due to lack of determination method and predicted calculation formula for characteristic strength in current GB 50005-2003 'Chinese code for design of timber structures', the coefficient or the order statistic value of characteristic strength is usually directly copied from foreign standard. In order to develop and improve the determination method for characteristic strength and to reasonably determine the characteristic strength, the confidence values under different coefficients of variation were analyzed by parametric and non-parametric methods in which the normal random sample was selected. Based on the analysis results by parametric method, relationships between the coefficient of characteristic strength and confidence level, number of specimens was obtained; while, based on that by non-parametric method, relationships between the order statistic value, confidence level and number of specimens were also obtained. The fitting formulas of the coefficient of characteristic strength and of the order statistic value were constructed. The analysis results of an example indicate that the calculation results by the fitting formulas are in good agreement with the actual results. [ABSTRACT FROM AUTHOR]