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Wood - Lumber Stress Grade & Design


Quiz Questions

1.For simplicity and economy in use, pieces of lumber of similar mechanical properties are placed in categories called stress grades, which are characterized by
one or more sorting criteria
a set of properties for engineering design
a unique grade name.
All of the above
2. The National Grading Rule provides guidelines for writing grading rules for lumber in this thickness range and specifies grading characteristics for different grade specifications.
True
False
3.What does ASTM stand for?
American Standard for Testing and Materials
American Society of Testing and Materials
American Standard of Transportation and Materials
None of the above
4.Visual grading is the original method for stress grading.
True
False
5.Approval process for acceptance of design values for foreign species:

  • Rules-writing agency seeks approval to include species in grade-rule book.
  • Agency develops sampling and testing plan, following American Lumber Standard Committee (ALSC) foreign importation guidelines, which must then be approved by ALSC Board of Review.
  • Lumber is sampled and tested in accordance with approved sampling and testing plan.
  • Agency analyzes data by ALSC Board of Review and ASTM D1990 procedures and other appropriate criteria (if needed).
  • Agency submits proposed design values to ALSC Board of Review.
  • ALSC Board of Review and USDA Forest Service, Forest Products Laboratory review submission.
  • Submission is available for comment by other agencies and interested parties.
  • ALSC Board of Review approves (or disapproves) design values, with modification (if needed) based on all available information.
  • Agency publishes new design values for species.
True
False
6.In general, knots have a greater effect on strength in tension than compression; in bending, the effect depends on whether a knot is in the tension or compression side of a beam (knots along the centerline have little or no effect).
True
False
7.The presence of a knot has a greater effect on most strength properties than on stiffness. The effect on strength depends approximately on:
the proportion of the cross section of the piece of lumber occupied by the knot
knot location
distribution of stress in the piece
All of the above
8.Slope of grain (cross grain) reduces the mechanical properties of lumber because the fibers are not parallel to the edges.
True
False
9.Checks are separations of the wood through the piece to the opposite surface or to an adjoining surface caused by tearing apart of the wood cells. Splits are a separation of the wood that normally occur across or through the annual rings, usually as a result of seasoning.
True
False
10.Shake is a separation or a weakness of fiber bond, between or through the annual rings, that is presumed to extend length-wise without limit.
True
False
11.Properties assigned to lumber are sometimes modified by using the rate of growth and percentage of late wood as measures of density.
True
False
12.Decay in most forms should be prohibited or severely restricted in stress grades because the extent of decay is difficult to determine and its effect on strength is often greater than visual observation would indicate.
True
False
13.Wane refers to bark or lack of wood on the edge or corner of a piece of lumber, regardless of cause (except eased edges).
True
False
14.For a beam containing an edge knot, the bending strength ratio can be idealized as the ratio of the bending moment that can be resisted by a beam with a reduced cross section to that of a beam with a full cross section:
	Wood - Lumber Stress Grade & Design

Where:
SR=strength ratio,
k=knot size, and
h =?
What does h mean?

Width of face containing the knot
Height
Size of the beam
None of the above
15.What does figure 6-2 illustrate about? (Refer Pg 6-6)
Effect of edge knot: A, edge knot in lumber and B, assumed loss of cross section (cross-hatched area).
Visual grades described in National Grading Rule
Relation between strength and strength ratio
None of the above
16.Modulus of elasticity E is a measure of the ability of a beam to resist deflection or of a column to resist buckling.
True
False
17.Quality control procedures are necessary to ensure that stresses assigned by a machine-grading system reflect the actual properties of the lumber graded.
True
False
18.As wood is cooled below normal temperatures, its properties increase. When heated, its properties decrease. The magnitude of the change depends upon moisture content.
True
False
19.Machine-graded lumber is lumber evaluated by a machine using a nondestructive test followed by visual grading to evaluate certain characteristics that the machine cannot or may not properly evaluate.
True
False
20.Pitch pockets ordinarily have so little effect on structural lumber that they can be disregarded in stress grading if they are small and limited in number.
True
False