ASTM D 5457c

This specification covers procedures for computing the reference resistance of wood-based materials and structural connections for use in load and resistance factor design (LRFD). Parameters required for the derivation of reference resistance are presented. These parameters include the distribution percentile, coefficient of variation, data confidence factor, and reliability normalization factor. The shape and scale parameters of the two-parameter Weibull distribution shall be established to define the distribution of the material resistance. The data confidence factor accounts for uncertainty associated with data sets. This factor, which is a function of coefficient of variation, sample size, and reference percentile, is applied as a multiplier on the distribution estimate. The reliability normalization factor is used to adjust the distribution estimate to achieve a target reliability index. The reliability normalization factor is the ratio of the computed resistance factor to the specified resistance factor, adjusted by a scaling factor.