1996 LRFD Manual for Engineered Wood Construction

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LRFD MANUAL FOR ENGINEERED WOOD CONSTRUCTION31TENSIONMEMBERS33.1 General 323.2 Design 323.2.1 Adjustment Factors 323.3 Special Considerations 333.3.1 Net Section Calculation 333.3.2 Radial Tension in CurvedMembers 333.4 Checklist: Using Tension MemberSelection Tables 333.5 Design Examples 33Example 3-1: Truss Bottom Chord 33Example 3-2: Bolted Truss BottomChord 34AMERICAN FOREST & PAPER ASSOCIATION
32 TENSION MEMBERS3.1 General InformationThis chapter covers design of members stressed primarilyin tension parallel to grain. Examples of suchmembers include truss members and diaphragm chords.See specific product supplements for factored tensionresistance values (tension member selection tables) andreference tension strengths.The designer is advised that use of wood members inapplications that induce tension perpendicular to grainstresses should be avoided.3.2 DesignThe basic equation for design of tension members(AF&PA/ASCE 16-95 Eq. 3.1-1) is:whereλφ tT′ $ T uλ = time effect factor (see AF&PA/ASCE 16-95Table 1.4-2)φ t= 0.80T′ = adjusted tension resistance parallel to grain= factored tensile forceT uThe factored tension resistance is tabulated in the tensionmember selection tables of individual productsupplements. The tabulated values are suitable for membersthat conform to all conditions of the checklist inSection 3.4.3.2.1 Adjustment FactorsMembers that do not meet all conditions in the checklistmust be designed by adjusting the tabulated tensionresistance values or by applying all applicable adjustmentfactors to the reference tension strength for the product.The complete equation for calculation of factored tensionresistance is:λφ tT′ = λφ tF t′AC MC tC FC ptC rtis 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.is the size factor for visually graded sawn lumberor round timber members. Tabulated resistancesalready include the size factor. For calculationsstarting from reference tension strengths, use thevalue of C F given in the Structural Lumber Supplementor Timber Pole and Pile Supplement.is the preservative treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with preservative chemicals, use thevalue of C pt given in the product supplement orguideline.is the fire-retardant treatment factor. Tabulated resistancesare for untreated members. For membersthat are treated with fire-retardant chemicals, usethe value of C rt given in the product supplement orguideline.whereA = area (in 2 )F t′ = F tC MC tC FC ptC rtFor untreated members used in a normal building environment(meeting the reference conditions of Sec. 1.1.5)the general equation for F t ′ reduces to:F t= reference tension strength (ksi)F t′ = F tC FAMERICAN WOOD COUNCIL
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Page 4 and 5: TABLE OF CONTENTSChapter/TitlePageC
Page 6 and 7: iNotationAGross areaA nNet area, ne
Page 8 and 9: iiiP uCompressive or bearing force
Page 10 and 11: vGlossaryAdjusted resistance. The r
Page 12 and 13: viithickness (timbers), green shall
Page 14 and 15: ixPrefabricated wood I-joists. Pre-
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Page 18 and 19: GUIDELINELRFD MANUALTO LRFDFORFOREN
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1996 LRFD Manual for Engineered Wood Construction

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