2012 ASD/LRFD Manual for Engineered Wood Construction

6 M3: DESIGN PROVISIONS AND EQUATIONSM3.1 GeneralThis Chapter covers design of members for bending,compression, tension, combined bending and axial loads,and bearing.M3.2 Bending Members - GeneralThis section covers design of members stressed primarilyin flexure (bending). Examples of such membersinclude primary framing members (beams) and secondaryframing members (purlins, joists). Products commonlyused in these applications include glulam, solid sawn lumber,structural composite lumber, and prefabricated I‐joists.Bending members are designed so that no design capacityis exceeded under applied loads. Strength criteriafor bending members include bending moment, shear, localbuckling, lateral torsional buckling, and bearing.See specific product chapters for moment and shearcapacities (joist and beam selection tables) and referencebending and shear design values.M3.3 Bending Members - FlexureThe basic equation for moment design of bendingmembers is:M′ ≥ M (M3.3-1)The equation for calculation of adjusted momentcapacity is:M′ = F b ′ S (M3.3-2)where:M′ = adjusted moment capacitywhere:S = section modulus, in. 3M = bending momentF b ′ = adjusted bending design value, psi.See product chapters for applicableadjustment factors.M3.4 Bending Members - ShearThe basic equation for shear design of bending membersis:V′ ≥ V (M3.4-1)where:V′ = adjusted shear capacity parallel tograin, lbsV = shear force, lbsThe equation for calculation of shear capacity is:V′ = F v ′ Ib/Q (M3.4-2)which, for rectangular unnotched bending members,reduces to:V′ = 2/3 (F v ′) A (M3.4-3)where:I = moment of inertia, in. 4A = area, in. 2F v ′ = adjusted shear design value, psi.See product chapters for applicableadjustment factors.AMERICAN WOOD COUNCIL