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. Load Deflection Limit of Span/360, Load Duration Factor of 1.00. No.2 grade of structural dimension lumber and structural timber, reference WWPA Western Lumber Grading Rules 2021 Sections 42.12, 62.12, 70.12, and 80.12.Western Cedars is a species group of any combination of Incense, Western Red, Alaska and Port Orford Cedar.Load in Pounds per Lineal Foot of Total Load (Live + Dead Loads).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.
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