Mechanical grading of oak timbers

      For many wood species, the grading of timbers [>76 mm (>4-in.) thick] has not changed in decades. Most timbers are still visually graded by methods that originated in the 1930s. Mechanical grading procedures used to accurately grade 38-mm (2-in. nominal) dimension lumber have not been adapted for use with timbers. Furthermore, the only reliable timber test data available for most softwood species were obtained near the turn of the 20th century, and no test data are available for hardwood timber. The lack of better grading procedures and test data makes it likely that current property assignments for timbers are wasteful. Given that the reduced availability of lumber is expected to continue well into the 21st century, the structural engineer must have the widest possible options for structural timbers. Therefore, a study was conducted by the USDA Forest Service, Forest Products Laboratory, to examine use of a pulse echo stress wave technique along the length of timbers to estimate modulus of elasticity (MOE) of green timbers and the development of a machine stress rated grade for oak timbers. Two hundred and ninety-five untreated 178- by 229-mm (7- by 9-in.) mixed oak timbers, 4.9 m (16 ft) in length, were measured weighted, and nondestructively evaluated to determine their pulse echo MOE. Two hundred twenty were destructively tested in bending; 75 were tested to failure in compression parallel to the grain. The results of these tests determined relationships between pulse echo MOE and static bending MOE and between bending and compressive strength. These tests suggests a clear potential of establishing a machine stress rated grade for oak timbers. This article discusses the implication of these results, potential commercial grades, and a follow-up study to qualify the suggested grades. 1999

This article is in PDF format (file size: 267 kb). To download this article, right click on the link immediately below and choose "save target as". To view the article, left click the link immediately below.
(Download the latest Acrobat Reader if required.)

Mechanical grading of oak timbers   (1999)

For many wood species, the grading of timbers [>76 mm (>4-in.) thick] has not changed in decades. Most timbers are still visually graded by methods that originated in the 1930s. Mechanical grading procedures used to accurately grade 38-mm (2-in. nominal) dimension lumber have not been adapted for use with timbers. Furthermore, the only reliable timber test data available for most softwood species were obtained near the turn of the 20th century, and no test data are available for hardwood timber. The lack of better grading procedures and test data makes it likely that current property assignments for timbers are wasteful. Given that the reduced availability of lumber is expected to continue well into the 21st century, the structural engineer must have the widest possible options for structural timbers. Therefore, a study was conducted by the USDA Forest Service, Forest Products Laboratory, to examine use of a pulse echo stress wave technique along the length of timbers to estimate modulus of elasticity (MOE) of green timbers and the development of a machine stress rated grade for oak timbers. Two hundred and ninety-five untreated 178- by 229-mm (7- by 9-in.) mixed oak timbers, 4.9 m (16 ft) in length, were measured weighted, and nondestructively evaluated to determine their pulse echo MOE. Two hundred twenty were destructively tested in bending; 75 were tested to failure in compression parallel to the grain. The results of these tests determined relationships between pulse echo MOE and static bending MOE and between bending and compressive strength. These tests suggests a clear potential of establishing a machine stress rated grade for oak timbers. This article discusses the implication of these results, potential commercial grades, and a follow-up study to qualify the suggested grades.

Author: Kretschmann, David E.; Green, David W.

Source: Journal of materials in civil engineering. Vol. 11, no. 2 (May 1999).:p. 91-97 : ill.

Citation: Kretschmann, David E.; Green, David W.  1999.  Mechanical grading of oak timbers   Journal of materials in civil engineering. Vol. 11, no. 2 (May 1999).:p. 91-97 : ill..

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?


Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: FPL (Forest Products Laboratory)

  • KnowledgeBase: Forestry

  • KnowledgeBase: FPL (Forest Products Laboratory)


    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.



    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2016 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB











  • WOODWEB - the leading resource for professional woodworkers


      Home » Knowledge Base » Knowledge Base Article