Flexural properties of visually graded southern pine structural lumber were evaluated. Several grade controlling characteristics were considered relative to bending properties and compared with current design values. A total of 751 southern pine lumber specimens were obtained from a broad spectrum of regions in the southeastern United States. Visually graded No. 2, nominally two inch thick specimens, in four and six inch widths, were obtained from commercial sawmills. All specimens were evaluated by a certified grader in the laboratory. Actual dimensions, weight, and moisture content (MC) were measured. Growth and manufacturing related characteristics were identified and classified into two categories: strength reducing characteristics (SRC) and grade reducing characteristics (GRC). Specific gravity (SG), bending modulus of elasticity (MOE), and modulus of rupture (MOR), were determined for each specimen. The presence of knots was identified as the most significant SRC; their presence had the most significant impact on SG, MOE and MOR. For GRC, specimens with knots, warp and specimens that fell into the category none, were significantly lower in SG, MOE and MOR. MOE and the allowable design bending strength values yielded in this study met the current design value criteria for both widths tested.
Bibliographical noteFunding Information:
The authors acknowledge the support of the US Department of Agriculture (USDA) Research, Education, and Economics; Agriculture Research Service; Administrative and Financial Management; Financial Management and Accounting Division; and Grants and Agreements Management Branch under Agreement No. 58-0202-4-001. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the USDA. The authors acknowledge the support from USDA Forest Service Forest Products Laboratory in Madison, Wisconsin as a major contributor of technical assistance, advice, and guidance to this research. This paper was approved as journal article SB1045 of the Forest & Wildlife Research Center, Mississippi State University.
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- Grading lumber
- Strength reducing characteristics