Analysis of the Part I Southern Pine In-Grade Program Data

Abstract

It has been suggested that within- and between-mill variability of samples may have changed since the original North American In-Grade Program and a new sampling method may be required. The cooperative research “In-Grade Program” was conducted in the late 1970s to the late 1980s to establish allowable properties (modulus of elasticity (MOE), allowable bending stress (F_b), allowable compressive stress parallel to grain (F_c), and allowable tensile stress parallel to grain (F_t)) for dimension lumber based on full-size testing of graded lumber. The In-Grade Program was divided into three major administrative parts, each with specific objectives. Part I estimated bending strength and stiffness of 2 by 8 No. 2 and 2 by 4 STUD grades of Douglas-fir and Southern Pine. Part II considered other grades, sizes, and methods of loading (such as tension and compression parallel to the grain) for Douglas-fir and Southern Pine. Part III considered other species. The purpose of this document is to explain how Part I of the In-Grade Program, which looked at regional and mill variability, was designed and to re-examine the analysis that was conducted in 1980 to determine sampling methods. The present report discusses Southern Pine data, and sampling design issues related to regions, mills, and pieces sampled in a mill are presented. Also, other techniques not applied in 1980 are used to reanalyze the test data. The random sampling of mills within region based on production was based on a balancing of the significance of regional, mill-to-mill, and within-mill variability. We feel that the decisions that were made in setting up the stratified cluster sampling methods to minimize variability in sampling for Part II and Part III were justified and necessary given the limited resources available to conduct Part II and Part III of the program.

Citation

Evans, James W.; Kretschmann, David E; Hatfield, Cherilyn A.; Green, David W. 2013. Analysis of the Part I Southern pine in-grade program data. Gen. Tech. Rept. FPL-GTR-221. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 15 p.