Calculating strength ratio and grade quality index of dimensional lumber using ASTM D4761 and ASTM D245

Abstract

The standard for calculating grade quality index (GQI) is a three-step process. First, failure codes are assigned during testing. Second, strength ratios are calculated from failure codes recorded during post-test analysis, not including failure from slope of grain. Third, the lower fifth percentile strength ratio is identified, which is defined as the GQI. In the past, the process of calculating strength ratios required one to correctly interpret and apply calculations per ASTM D4761 (current edition) and ASTM D245 (current edition) or gain remote access to USDA Forest Service, Forest Products Laboratory servers, transfer the failure codes to the servers using file transfer protocol, instruct the resident “SRatio” Fortran program to operate on the transferred files, and then transfer the files back to the local computer. Although the latter yielded consistent and reliable strength ratios, the process was slow and cumbersome and relied upon access to outside computational resources that can now be made available on a local platform. The intended users of this report are those developing design values or performing monitoring programs of dimension lumber. This report describes the process and calculations behind the SRatio program to allow it to be re-created in commonly available applications, such as Excel (Microsoft Corporation, Redmond, Washington, USA). The Excel spreadsheet created and described in this report takes the failure code data from testing and calculates both strength ratios and GQI of the tested lumber samples, which is necessary for determining design values of the tested lumber sample.

Citation

Farber, Benjamin; Senalik, C. Adam. 2021. Calculating strength ratio and grade quality index of dimensional lumber using ASTM D4761 and ASTM D245. General Technical Report FPL-GTR-284. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 15 p