2012 ASD/LRFD Manual for Engineered Wood Construction

8 M3: DESIGN PROVISIONS AND EQUATIONSM3.7 Solid ColumnsSlenderness Considerations andStabilityThe user is cautioned that stability calculations arehighly dependent upon boundary conditions assumed inthe analysis. For example, the common assumption of apinned-pinned column is only accurate or conservative ifthe member is restrained against sidesway. If sidesway ispossible and a pinned-free condition exists, the value ofK e in NDS 3.7.1.2 doubles (see NDS Appendix Table G1for recommended buckling length coefficients, K e ) and thecomputed adjusted compression parallel to grain capacitydecreases.M3.8 Tension MembersThis section covers design of members stressedprimarily in tension parallel to grain. Examples of suchmembers include shear wall end posts, truss members, anddiaphragm chords.The designer is advised that use of wood membersin applications that induce tension perpendicular to grainstresses should be avoided.M3.8.1 Tension Parallel to GrainThe basic equation for design of tension members is:T′ ≥ T (M3.8-1)where:T′ = adjusted tension parallel to graincapacity, lbsT = tensile force, lbsThe equation for calculation of adjusted tension capacityis:T′ = F t ′A (M3.8-2)where:A = area, in. 2F t ′ = adjusted tension design value, psi.See product chapters for applicableadjustment factors.Net Section CalculationDesign of tension members is often controlled by theability to provide connections to develop tensile forceswithin the member. In the area of connections, one mustdesign not only the connection itself (described in detailin Chapter M10) but also the transfer of force across thenet section of the member. One method for determiningthese stresses is provided in NDS Appendix E.M3.8.2 Tension Perpendicular toGrainRadial Stress in Curved MembersStresses induced in curved members under load includea component of stress in the direction of the radiusof curvature. This stress is traditionally called radial tension.Radial stress design is a specialized considerationthat is covered in NDS 5.4.1 and is explained in detail inthe American Institute of Timber Construction (AITC)Timber Construction Manual.M3.9 Combined Bending and Axial LoadingThis section covers design of members stressed undercombined bending and axial loads. The applicable strengthcriteria for these members is explicit in the NDS equations– limiting the sum of various stress ratios to less than orequal to unity.Bending and Axial TensionFor designs in which the axial load is in tension ratherthan compression, the designer should use NDS Equations3.9-1 and 3.9-2.AMERICAN WOOD COUNCIL