2001 ASD Supplements - unprotected PDF - American Wood Council

SP-36SUPPLEMENTAL DESIGN ASSISTANCETable 7.5Application Adjustment FactorsDuration of Load, C D (Applies to Bending and Shear Only)Permanent load (over 10 years) 0.902 months, as for snow 1.157 days 1.25Wind or Earthquake1.60 aImpact 2.00Span Adjustment2-span to 1-spanDeflection 0.42Bending 1.00Shear 1.253-span to 1-spanDeflection 0.53Bending 0.80Shear 1.20Wet or Damp Locations, C M (Moisture Content 16% or more)aDeflection 0.85Bending 0.75Shear 0.75Check local building code.7.3 Design ExamplesExample 1: Conventional RoofA 4-ply plywood, single floor 24 oc panel with tongueand-grooveedges was inadvertently installed over4-in.-nominal roof supports 48 in. on center. The long dimension(strength axis) of the panel was placedperpendicular to supports. The local building code requiresthat the panel support a 25-psf snow load.Bending StrengthFrom Table 3.1, a single floor 24 oc panel with stressapplied parallel to the strength axis (long panel dimensionperpendicular to supports) has a bending strengthcapacity (F b S) of 640 lb.-in./ft. This capacity is adjustedby a C G factor of 1.1 as shown in Table 3.1.1 for 4-plyplywood and by duration-of-load factor (C D ) of 1.15 (seeSection 4.3). From Section 7.1, a two-span condition isassumed.wb96FbS=l 1296 ( 640× 1.1×1.15)=248= 34 psfShear Strength in the PlaneFrom Table 3.3, a single floor 24 oc panel with stressapplied parallel to the strength axis has shear strength inthe plane (F S [Ib/Q]) of 250 lb./ft. This capacity is adjustedby a C G factor of 1.2 as shown in Table 3.3.1 for 4-plyplywood and by a duration-of-load factor (C D ) of 1.15(see Section 4.3).ws( I )19.2 Fsb/Q=l219.2 250 x 1.2 x 1.15== 149 psf( )( 48 − 3.5)APA – The Engineered Wood Association