MSR Stressed for success

systems and better reliability on roof structures." The assumed Coefficient of Variance (COV) for E in MSR lumber grades is 0.11, allowing for the necessary distribution of the load in a wooden structure. A less stiff component, such as visually graded lumber, whose assumed COV for E is 0.25, results in more of the load being applied to fewer components, reducing the overal rigidity of the structure and reducing reliability.

These examples of the virtues of MSR lumber are also good selling points for dealers to utilize to interest builders to purchase the product. Another of MSR lumber's strong suits is better uniformity among suppliers. After all, the consistent rating system of the product extends throughout the industry, allowing builders to shop for the best price without having to worry about sacrificing quality. Likewise, MSR grades can be produced from different wood species from various sources, enabling builders to maintain their confidence in the product's quality even if they switch to a less expensive supply.

f UMBER retailers and distributors know that premium I-lquality lumber is imperative for a successful construction project. These professionals prosper or perish by the wood they sell. With this in mind, how can dealers be assured that their lumber is top quality?

Machine Stress Rated (MSR) lumber is one possible answer. Lumber that passes the MSR inspection has met specifications called for by the grade stamp. As a result, MSR lumber is less likely to fail under its rating than visually inspected lumber.

"Weak boards cause the majority of problems in lumber applications," asserts James D. Logan, president of Metriguard Inc., Pullman, Wa., an MSR equipment manufacturer. "A direct physical measurement of lumber's mechanical properties is more reliable and accurate than estimates based on visual inspection alone."

As opposed to visually inspecting lumber that passes by at 50 to 60 lugs per minute, the physical properties of each piece of MSR lumber are measured during prodution. According to Logan, the MSR process "weeds out weak lumber." He further notes that the results of each MSR inspection are verified each shift by a sample test of five to 10 pieces. With such an onslaught of boards to look at during a visual inspection, it is not uncommon for a human to miss slope-of-grain defects or shake failures that a bending testing machine would detect.

The failure of lumber during or after construction is laborious and expensive to correct for all concerned, to say nothing of being a reputation wrecker for a dealer. MSR lumber has less variability in stiffness, allowing for designs that hold to tighter tolerances and guard against expensive failures. "With MSR lumber, you have better control over the elasticity value (E-value) of the wood," says Logan. "Therefore, you have better control over the bounce in floor

Assured quality also reduces the percentage ofdiscarded lumber at a iob site. "Contractors and builders are able to utilize more of the material they purchase because all MSR lumber must pass stringent physical standards in order to earn its grade," maintains Logan.

As a vote of confidence, more than 1.1 billion bd. ft. of MSR lumber was produced in 1991