1996 LRFD Supplements - unprotected PDF - American Wood Council

LRFD STRUCTURAL LUMBER SUPPLEMENT33C t is 1.0C pt is 1.0C rt is 1.0unless temperatures exceed 100°F for extendedperiods of time, or as shown in Table4.2 otherwisefor members that are untreated orpreservatively treated in accordance with approvedstandardsfor members that are not fire-retardant treated.For fire-retardant treated members, the valueof C rt shall be established by the supplier ofthe treated products or treatment chemicalsC F is as shown in Table 4.3C P is 1.0for fully supported or “zero length” columns,or as given in AF&PA/ASCE 16-95 Section4.3 otherwiseBending (Moment and Shear)The unfactored resistances for bending members canbe computed by the following equations:For moment:M′ = Fb N SFor shear:V ′ = F vN I bQwhereM′ and V′ are the adjusted moment resistance(unfactored) and adjusted shear resistance (unfactored),F b ′ and F v ′ are the adjusted bending strength and adjustedshear strength, S is the section modulus, I is the momentof inertia, b is the member width and Q is the staticalmoment.The adjusted bending and shear strengths are computedby multiplying the reference strengths by a seriesof adjustment factors.The reference values for F b and F v are tabulated inChapter 3 of this supplement for all species and gradeslisted in the 1991 NDS.F N = F ( C C C C C C C C C )b b M t pt rt L F fu r fC M is 1.0C t is 1.0C pt is 1.0C rt is 1.0C r is 1.15for 19% MC and less, or as shown in Table4.1 otherwiseunless temperatures exceed 100°F for extendedperiods of time, or as shown in Table4.2 otherwisefor members that are untreated or arepreservatively treated in accordance with approvedstandardsfor members that are not fire-retardant treated.For fire-retardant treated members, the valueof C rt shall be established by the supplier ofthe treated products or treatment chemicalsfor members used in a repetitive assembly asdefined in AF&PA/ASCE 16-95 Section 5.3,or 1.00 otherwiseC F is as shown in Table 4.3C L is 1.0C f is 1.0C H is 1.0C fu is 1.0for fully supported beams, or as given inAF&PA/ASCE 16-95 Section 5.2 otherwisefor rectangular members loaded along a principalaxis, or as given in AF&PA/ASCE 16-95Section 5.1 otherwisefor members with maximum splits or shakes,or as shown in Table 4.4 otherwisefor members loaded edgewise, or as shownin Table 4.5 for members loaded flatwiseCombined Axial & FlexuralThe resistances for members under combined axialand flexural loading are based upon the equations inAF&PA/ASCE 16-95 Chapter 6. Users are directed tothat section and to the discussion of tension, compressionand bending above.BearingThe required bearing areas of members are computedbased upon the following equations:4DESIGN ADJUSTMENT FACTORSandF N = F ( C C C )vv M t HFor end bearing:whereP N=F N Ag g g