Evaluation of Bending Strength Ratios for Eastern Oak Pallet Lumber
Keywords:Strength ratio, pallet lumber, lumber defects, visual stress rating, modulus of rupture
AbstractVisual stress rating using strength ratios is the only expedient and currently available method of assigning strength design values to pallet shook. In this study, the estimated bending strength ratio (ESR), determined from ASTM D245, and the actual bending strength ratio (ASR), determined through testing, were compared for over two thousand two hundred pieces of eastern oak pallet lumber. The ESR generally underestimated the ASR for stringers and deckboards with knots and slope of grain. The ESR increasingly underpredicted the ASR as knot size increased. The ESR consistently under-predicted the ASR throughout the range of severity of slope of grain. If assigners of design stresses for pallet shook use ASTM strength ratios, then conservative strength estimates will result; this is particularly true for low quality material.
American Society for Testing and Materials. 1986. Standard D 198-84. Standard methods of static tests of timbers in structural sizes. Annual Book of ASTM Standards, vol. 04.09.nAmerican Society for Testing and Materials. 1986. Standard D 245-81 (reapproved 1986). Standard methods for establishing structural grades and related allowable properties for visually graded lumber. Annual Book of ASTM Standards, vol. 04.09.nAmerican Society for Testing and Materials. 1986. Standard D 2555-81. Standard methods of establishing clear wood strength values. Annual Book of ASTM Standards, vol. 04.09.nAmerican Society for Testing and Materials. 1986. Standard D 2915-84. Standard methods of evaluating allowable properties for grades of structural lumber. Annual Book of ASTM Standards, vol. 04.09.nBohannan, Billy. 1966. Effect of size on bending strength of wood members. U.S. Forest Service Research Paper FPL 56. Madison, WI.nDoyle, D. V., and L. J. Markwardt. 1966. Properties of southern pine in relation to strength grading of dimension lumber. U.S. Forest Service Research Paper FPL 64. Madison, WI.nKoch, C. B. 1981. Prediction of bending strength of yellow-poplar 2 x 4's from estimated strength ratios. For. Prod. J. 31(7):53-55.nMcLain, T. E., and J. S. Holland. 1982. Preliminary evaluation of the strength and stiffness of yellow-poplar pallet shook. For. Prod. J. 32(11/12):51-56.nMcLain, T. E., H. W. Spurlock, J. A. McLeod, and W. B. Wallin. 1986. The flexural properties of eastern oak pallet lumber. For. Prod. J. 36(9):7-G.nMcLeod, J. A. 1985. Development of flexural design values for pallet shook. M.S. thesis, Dept. of Forest Products, Virginia Tech, Blacksburg, VA.nRousis, W. T., and C. B. Koch. 1976. W. Va. Forestry Notes. No. 6, pp. 7-11.nSardo, W. H., and W. B. Wallin. 1974. The performance of wooden pallets in pallet exchange programs. National Wooden Pallet and Container Association. Washington, D.C.nWalters, C. S., J. K. Guiher, and H. W. Norton. 1971. The statistical reliability of predicting bending strength from strength-ratio tables. For. Prod. J. 21(6):47-57.nWilson, T. R. C. 1921. Effect of spiral grain on the strength of wood. J. For. 19(7):1-8.nWilson, T. R. C. 1934. Guide to the grading of structural timbers. Miscellaneous Publication 185. U.S. Dept. of Agriculture.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.