2001 ASD Supplements - unprotected PDF - American Wood Council

GL-16DESIGN ADJUSTMENT FACTORS4.9 Volume Factor, C vAllowable bending stresses of glued laminated timberare affected by geometry and size. Generally, largersizes have a correspondingly lower allowable bendingstress than smaller members. To account for this behavior,a volume factor, C v , shall be applied. C v shall notexceed 1.0 and is computed as follows:C V= (21/L) 1/x (12/d) 1/x (5.125/b) 1/x ≤ 1.0 (4.1)L = length of bending member between points ofzero moment, ft.d = depth of bending member, in.b = width (breadth) of bending member. For multiplepiece width layups, b = width of widest pieceused in the layup. Thus, b ≤ 10.75"x = 20 for Southern Pinex = 10 for all other speciesNote that separate exponent values are given for Westernspecies and for Southern Pine. No volume adjustmentis required for properties other than allowable bendingstresses when the load is applied perpendicular to the wideface of the laminations. Tables 4.5 and 4.6 give some C vvalues for Western species and Southern Pine glued laminatedtimbers, respectively.4.10 Curvature Factor, C cThe curvature factor, C c , is used to adjust the allowablebending stresses of curved glued laminated timbermembers only. It takes into account the difference in extremeouter fiber stress between a curved member and astraight prismatic member, as well as any residual stressesthat may remain in a lamination that has been bent to thestated curvature. However, the curvature factor, C c , shallnot be applied to the allowable bending stress in the straightportion of a member, regardless of curvature in other portions.Also, this factor is not applicable to cambered gluedlaminated timber members or in the design of pitched andtapered curved glued laminated timber members. The curvaturefactor, C c , shall be calculated in accordance withthe following equation:tCc = 1 −20002( ) [4.2]Rwhere:t = thickness of lamination, in.R = radius of curvature of inside face of lamination,in.t/R ≤ 1/100 for hardwoods and Southern Pinet/R ≤ 1/125 for other species4.11 Flat Use Factor, C fuTable 4.4 Flat Use Factor a , C fuAllowable bending stresses of glued laminated timbershall be adjusted by the flat use factor, C fu , when loadedin bending parallel to wide faces of the laminations (they-y axis). The allowable bending stresses in the parallelto wide faces of the laminations, F by , as given in Tables3.1 and 3.2 of this Supplement, are based on memberswith laminations 12 inches wide. For members with laminationsless than 12 inches wide, the tabulated F by valuesshall be adjusted by a flat use factor, C fu , as listed in Table4.4. When the width of the laminations is greater than 12inches, as may occur in members with multiple-piece laminations,C fu shall be obtained by use of the equation givenin footnote (a) to Table 4.4.aMember Dimensions Parallel toWide Faces of LaminationsC fu10-3/4 or 10-1/2 1.018-3/4 or 8-1/2 1.046-3/4 1.075-1/8 or 5 1.103-1/8 or 3 1.162-1/2 1.19Values for C fu are rounded values from the equation (12/d) 1/9 where d isthe dimension of the wide faces of the laminations.APA – The Engineered Wood Association