The result is a more precise understanding of the strength of each piece of lumber than is possible with visually graded lumber, which allows designers to use full-design strength and avoid overbuilding. Machine grading measures a characteristic such as stiffness or density that correlates with the structural properties of interest, such as bending strength. Machine stress-rated and machine-evaluated lumber is readily available for end-uses where high strength is critical, such as truss rafters, laminating stock, I-beams and web joints. Resulting declines in lumber quality have been of concern to both the lumber industry and consumers and have caused increased use of alternative construction products.

The Canadian Lumber Standards Accreditation Board (CLSAB) monitors the quality of Canada's lumber grading and identification system.Īttempts to maintain lumber quality over time have been challenged by historical changes in the timber resources of the United States?from the slow-growing virgin forests common over a century ago to the fast-growing plantations now common in today's commercial forests. The National Lumber Grades Authority (NLGA) is responsible for writing, interpreting and maintaining Canadian lumber grading rules and standards. Grades standardize the quality of lumber at different levels and are based on moisture content, size and manufacture at the time of grading, shipping and unloading by the buyer. A summary of the six published design values?including bending (Fb), shear parallel to grain (Fv), compression perpendicular to grain (Fc-perp), compression parallel to grain (Fc), tension parallel to grain (Ft), and modulus of elasticity (E and Emin) can be found in Structural Properties and Performance published by WoodWorks.Ĭanada has grading rules that maintain a standard among mills manufacturing similar woods to assure customers of uniform quality. Design Values for Wood Construction, which is a supplement to the ANSI/AF&PA National Design Specification? for Wood Construction, provides these lumber design values, which are recognized by the model building codes. The applicable standards are based on results of tests conducted in cooperation with the USDA Forest Products Laboratory. Current standards are set by the American Lumber Standard Committee, appointed by the Secretary of Commerce.ĭesign values for most species and grades of visually graded structural products are determined in accordance with ASTM standards, which consider the effect of strength reducing characteristics, load duration, safety and other influencing factors. These standards have changed over the years to meet the changing needs of manufacturers and distributors, with the goal of keeping lumber competitive with other construction products.

The move to set national standards for lumber in the United States began with publication of the American Lumber Standard in 1924, which set specifications for lumber dimensions, grade, and moisture content it also developed inspection and accreditation programs. Therefore, they vary considerably in strength, utility and value. Individual pieces of lumber exhibit a wide range in quality and appearance with respect to knots, slope of grain, shakes and other natural characteristics. Structural Wood Lumber Engineering Properties | Modulus of Elasticity of Wood | Wood Engineering Design Data.Structural Wood Lumber Engineering Properties 5' and Larger

Actual size of 8 inches block