In our October article, Because Good Ingredients Matter, we focus on the word quality and the many ways that MSR lumber has become synonymous with high quality structural building components. Having laid the groundwork for why MSR has become so important for optimizing truss designs and an increasing potential to lower installed costs, this month we’ll take a look at another important piece of the puzzle: confidence.
For more than 60 years, MSR lumber has documented and tested structural design values. In contrast to visual grades, machine graded lumber is produced by measuring physical properties of each piece of lumber in the production line, and manufacturers are required to test samples during each shift. Machine graded lumber certification and quality control procedures are based on lumber standards approved by the American Lumber Standards (ALS) Committee or the Canadian Lumber Standards (CLS) Accreditation Board, and QC testing takes place on a per-shift basis for all machine graded lumber products.
Depending on the grade requirements, machine graded lumber is tested for one or more of the following engineering characteristics of wood: E, Fb, and Ft (as defined in the graphic [For image, See PDF or View in Full Issue.]). There are three major types of grading machines available today. The first type directly measures the stiffness of the lumber. The Continuous Lumber Tester (CLT) is the most common type of stiffness-based grading machine in use. The second type of machine directly measures the density of the lumber. The X-ray Lumber Gauge (XLG) is the most common type of density-based grading machine in use. The third type of machine uses acoustic resonance and density to calculate the stiffness of the lumber.
These machines identify the lumber based on algorithms keyed to the predictor property (either stiffness or density). Specific visual overrides are applied and per-shift off-line testing is performed to verify the assigned properties. Because 100 percent of the production goes through the machine and the process is verified each shift, each board is sorted on the same parameters, ensuring production is uniform and predictable.
This non-destructive testing process verifies that production meets design requirements for all product shipped to customers. This means that, even as timber growing practices and environmental conditions change, the process ensures the consistent strength and performance of each board.
As with visual grades of lumber, machine graded lumber is identified by the grade stamp of a lumber grading agency approved by the ALS and CLS. The distinguishing characteristics of the grade stamps for machine graded lumber include supplementary design values for the grade. For MSR, the grade stamp includes both the allowable bending stress (Fb) and bending stiffness (E).
For more resources on MSR technology, including a video on MSR history and technology, visit the Education page of the MSRLPC website. If you’re interested in a more immersive MSR experience, plan now to attend the 2023 MSR Workshop, April 26–28 in San Antonio, Texas.