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February 2023 #15283 Page #112
Effects of Ripping Structural Truss Lumber By MiTek Staff
ow does ripping lumber, cutting a board along its length, affect its grade or strength values? Structural lumber is graded or inspected which provides designers, through the National Design Specification® (NDS®) for Wood Construction, the strength/design values for the lumber members. This process is accomplished by visually inspecting the entire board or passing the board through a testing machine.
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The lumber industry is overseen by the American Lumber Standard Committee (ALSC). This group is made up of lumber producers, distributors, and users. They review and approve the grading rules and design values that are submitted to them by the grading agencies and then published in NDS. Each grade of visual graded lumber has specific requirements for grain direction and slope, lumber defect size(s) and distribution. See Figure 1 for examples of lumber defects from the Metal Plate Connected Wood Truss Handbook. The same issues exist for Machine Graded Lumber. As reflected by the visual grading rules, there is a known relationship between lumber defect size(s) and distribution and strength values.
Figure 1 – Images of Lumber Defects Continued next page
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