#Rafter span calculator full#

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:

#Rafter span calculator full#

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. Span Tablesīase Design Values For United States Only Sizes of rough and dressed Western Red Cedar are shown in Tables 1 and 2. Syy= Iyy /c = db2/6 = section modulus about the Y-Y axis (in.3) Sxx= Ixx /c = bd2/6 = section modulus about the X-X axis (in.3) Ryy= Square root of (Iyy/A) = b/Square root of 12 = radius of gyration about the Y-Y axis (in.) Rxx= Square root of (Ixx/A) = d/Square root of 12 = radius of gyration about the X-X axis (in.) Iyy= db3/12 = moment of inertia about the Y-Y axis (in.4) Ixx= bd3/12 = moment of inertia about the X-X axis (in.4) Y-Y= Neutral axis for flatwise bending (load applied to narrow face)ī= breadth of rectangular bending member(in.)ĭ= depth of rectangular bending member (in.)Ĭ= distance from neutral axis to extreme fiber of cross section (in.) X-X= neutral axis for edgewise bending (load applied to narrow face) The following symbols and formulas apply to rectangular beam cross sections: Section Modulus (S) is the moment of inertia divided by the distance from the neutral axis to the extreme fiber of the section.Ĭross Section is a section taken through the member perpendicular to its longitudinal axis. Moment of Inertia (I) of the cross section of beam is the sum of Table the products of each of its elementary areas multiplied by the square of their distance from the neutral axis of the section. Neutral axis, in the cross section of a beam, is the line in which there is neither tension nor compression stress. For convenience, the following are formulas to calculate the section properties of rectangular beam cross sections. Section properties are used in various design calculations.