Therefore, ASTM procedures for determining compression perpendicular to grain values are based on a deformation of 0.04″ and are considered adequate for most classes of structures. ASTM procedures consider deformation under bearing loads as a serviceability limit state comparable to bending deflection because bearing loads rarely cause structural failures. No split 1/2 x narrow face1 x narrow face 1-1/2 x narrow face or moreĪdjustments for Compression Perpendicular to Grain To Deformation Basis of 0.02″ĭesign values for compression perpendicular to grain are established in accordance with the procedures set forth in ASTM D 2555 and D 245. No split 1/2 x wide face 3/4 x wide face 1 x wide face 1-1/2 x wide face or more When length of split on wide face does not exceed When length of split on wide face does not exceed: When specific lengths of splits are known and any increase in them is not anticipated, the following adjustments may be applied: Horizontal shear values for 3″ and thicker lumber also are established as if a piece were split full length. Base Design Values for Use in the USA for Visually Graded (WCLIB, WWPA) Western Red Cedar 2-4″ Thick x 2″ and Widerīase values in pounds per square inch (psi) – Use with Adjustment Factors (see Tables 5 to 9)įor convenience, the table below may be used to determine horizontal shear values for any grade of 2″ thick lumber in any species when the length of split or check is known: Grades and sizes of Canadian dimension lumber are identical to those in use throughout the United States and conform to the requirements of applicable American Standards. The base design values apply to Western Red Cedar manufactured by members of the Western Red Cedar Lumber Association and graded to National Lumber Grading Authority (NLGA), West Coast Lumber Inspection Bureau (WCLIB) or Western Wood Products Association (WWPA) rules. To determine the value for a given size, the designer selects a base value for a given grade then multiplies the base value by a size factor from Table 5. These values are for use in the United States only. For Stud grade, the base strength values are published on a 2×6 basis. For Construction Standard and Utility grades, the base strength values are published on a 2×4 basis (the size factor is always 1.0). For Select Structural, No.1, No.2 and No.3 grades, the base strength values are published on a 2×12 basis. Base values are provided for a base size that depends on the grade. Since different sizes of visually-graded lumber have different values, the design values shown in Table 4 are tabulated in a base value approach. dead loadĭeflection – Limited in span in inches divided by 240 for live load onlyīase Design Values For United States Only RAFTER SPANS IN FOOT-INCH 30# SNOW LOAD 10# DEAD LOAD L/240ĭESIGN CRITERIA: Strength – 30 lbs.
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