NDT.net - March 2001, Vol. 6 No. 03

Forest Products Journal
Editor Erin Bosch,
Email: erin@forestprod.org
Forest Products Society

Lumber strength grading using x-ray scanning

Gary S. Schajer
Forest Products Society Member.
Published in Forest Products Journal J.51 (1) pp. 43-50.



Density scanning

Fig 2: Schematic diagram of a multiple-detector lumber density scanner. Fig 3: Typical measured density profile along the length of a board.

Strength-estimation method

Experimental procedure

Single-profile density measurements

Calibration stability

3-profile density measurements

Algorithm choice

Measured strength uncertainty

Board group no. Test type Known load position Unknown load position
r2 SEE r2 SEE

1 Tension 0.74 1,320 0.74 1,320
2 Tension 0.76 1,260 0.79 1,180
3 Bending 0.69 1,780 0.63 1,940
4 Bending 0.67 1,840 0.49 2,290
5 Bending 0.78 1,750 0.68 2,100
6 Compression 0.78 870 0.69 1,030
Table 7: Strength predictions with and without knowledge of load position.


Literature cited

  1. American Society for Testing and Materials. 1993. Standard practice for establishing structural grades and related allowable properties for visually graded lumber. Standard D 245-93. ASTM, West Conshohocken,Pa.
  2. __________. 1997. Standard test methods of static tests of lumber in structural sizes. Standard D 198-97. ASTM, West Consho-hocken, Pa.
  3. Bechtel, F.K. and J.R. Allen. 1995. Intro-duction to the Metriguard Model 72000 LS Lumber Tester. MSR Lumber Producers Council Meeting in Vancouver, B.C, Can-ada. Metriguard is in Pullman, Wash.
  4. CAE Newnes Ltd. X-ray Lumber Grader (XLG). Salmon Arm, B.C.
  5. DeVisser, D., W. Galligan, and S. Suddarth. 1993. Comparing machine stress-rated and visually graded lumber used in walls. Wood Design Focus 4(3):3-7.
  6. Hilbrand, H.C. and D.G. Miller. 1966. Ma-chine grading - theory and practice. Forest Prod. J. 16(11):28-40.
  7. Metriguard, Inc. Continuous Lumber Tester (CLT). Pullman, Wash.
  8. Müller, P.H. 1968. Mechanical stress-grading of structural timber in Europe, North America and Australia. Wood Sci. and Technology 2:43-72.
  9. National Institute of Standards and Technol-ogy. 1994. American Softwood Lumber Standard. Voluntary Product Standard PS 20-94. NIST, Gaithersburg, Md.
  10. Press, W.H., B.P. Flannery, S.A. Teukolsky, and W.T. Vetterling. 1986. Numerical Recipes. Cambridge Univ. Press, Cam-bridge, Mass.
  11. Schajer, G.S. 1989. Method and apparatus for estimating the strength of wood. U.S. Patent 4941357.
  12. USDA Forest Service. 1987. Wood Hand-book: Wood as an Engineering Material. Agri. Handb. 72. USDAForest Serv., Forest Prod. Lab., Madison, Wis.
  13. Western Wood Products Association. 1995. Standard grading rules for western lumber. WPPA, Portland, Oreg.
  14. Winistorfer, S.G. and R.D. Theilen. 1997. Machine-graded lumber - design implications. Wood Design Focus 8(2):14-20.
  15. Ziegler, G.A. 1997. Machine grading pro-cesses for softwood dimension lumber. Wood Design Focus 8(2):7-14.

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