ASTM D1990, gbsEstablishing Allowable Properties for Visually Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens,gcs is the consensus standard used to make submissions of allowable properties for many U.S., Canadian, and foreign species to the Board of Review of the American Lumber Standards Committee. Recently, it has become apparent how difficult it is to perform the calculations for such a submission. Some calculations are clearly specified in the standard; in some cases the standard merely indicates a need to make an adjustment but does not specify how to do so. This report discusses in detail how to develop allowable properties under the standard in a manner that is consistent with current practice. Many calculations in the standard are difficult and errors are easily made, particularly when using a spreadsheet; this report introduces a set of computer programs that perform some of the difficult calculations, thereby reducing the potential for errors. These computer programs can be run over the World Wide Web, or Fortran versions of the programs can be downloaded, compiled, and run on a usergass computer.

Accurate modeling of the joint stochastic nature of the strength properties of dimension lumber is essential to the determination of reliability-based design safety factors. This report reviews the major techniques for obtaining bivariate distributions and then discusses bivariate distributions whose marginal distributions suggest they might be useful for modeling the joint distribution of two strength properties. Finally, we pick a bivariate Weibull distribution and show that we can write its likelihood function under a proof loading scheme, offering the possibility that it can be used to model the joint distribution of two properties that must each be measured using a destructive test.