1996 LRFD Manual for Engineered Wood Construction

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LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION35COMPRESSIONMEMBERS44.1 General Information 364.1.1 Types of Columns 364.2 Design 364.2.1 Adjustment Factors 364.3 Special Considerations 374.3.1 Slenderness Considerations andStability 374.3.2 Net Section Calculation 374.3.3 Bearing Capacity Checks 374.3.4 Radial Compression in CurvedMembers 374.4 Checklist: Using Compression MemberSelection Tables 384.5 Design Examples 38Example 4-1: Glulam Column 38AMERICAN FOREST & PAPER ASSOCIATION
36 COMPRESSION MEMBERS4.1 General InformationThis chapter covers design of members stressed primarilyin compression parallel to grain. Examples of suchmembers include columns, truss members, and diaphragmchords.Information in this chapter is limited to the case inwhich loads are applied concentrically to the column. Provisionsof Chapter 6 should be used if loads are eccentricor if the compressive forces are applied in addition to bendingforces.See specific product supplements for factored compressionresistance values (column selection tables) andreference compression strengths.built-up columns are assembled from multiple pieces ofsimilar members connected in accordance with the NationalDesign Specification ® for Wood Construction.A composite column may have some elements with asufficiently different stiffness such that transformed sectionconcepts are required to accurately apportion the stressamong elements of the column.A spaced column must comply with provisions ofAF&PA/ASCE 16-95 Appendix A1. Note that this definitionincludes main column elements, spacer blocks withtheir connectors and end blocks with shear plate or splitring connectors.4.1.1 Types of ColumnsAF&PA/ASCE 16-95 differentiates between solid,built-up, composite and spaced columns. In this context4.2 DesignThe basic equation for design of compression members(AF&PA/ASCE 16-95, Eq. 4.1-1) is:where8N cP′ $ P u8 = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)N c= 0.90P′ = adjusted compression resistance parallel tograinP u= factored compressive forceThe factored compression resistance is tabulated inthe column selection tables of individual product supplements.The tabulated values are suitable for members thatconform to all conditions in the checklist in Section 4.4.whereC MC t8N cP′ = 8N cF c′AA = area (in 2 )F c′ = F cC MC tC FC PC ptC rt= reference compression strength (ksi)F cis the wet service factor. Tabulated resistances arebased on dry use. For wet service conditions, usethe value of C M given in the product supplement orguideline.is the temperature factor. Tabulated resistances arebased on temperature conditions that do not exceed100 ° F on a sustained basis. For higher temperatureconditions, use the value of C t given in the productsupplement or guideline.4.2.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting tabulated compressionresistance values or by applying all applicable adjustmentfactors to the reference compression strength for the product.The complete equation for calculation of factoredcompression resistance is:C Fis the size factor for visually graded sawn lumberor round timber members. Tabulated resistancesalready include the size factor. For calculationsstarting from reference compression strengths, usethe value of C F given in the Structural LumberSupplement or Timber Pole and Pile Supplement.AMERICAN WOOD COUNCIL
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Page 6 and 7: iNotationAGross areaA nNet area, ne
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1996 LRFD Manual for Engineered Wood Construction

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