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The bending and shear strength of plywood and OSB sheathing between wall studs is compared to the Component and Cladding (C&C) end zone wind load on the wall. The generated or user-input C&C loads are internally adjusted by 1.4 before being compared to the factored sheathing strength.
Sheathing bending capacity is determined for two sheathing orientations – the long direction being parallel or perpendicular to the studs, which creates sheathing loads that are analogous to 2-span or 3-span continuous beam loads. The weakest of shear and bending strength criteria for these situations is used as the strength.
The governing value of bending and shear resistance is given in the Components and Cladding by Shear Line table.
Deflection is not considered.
The bending resistance is given by the following:
j b mp KD / s2
and the shear resistance by
j b vpb KD / s
where
j : Factor from CSA O86 9.5.2 (bending) and 9.5.4 (shear) = 0.95
b : A factor for no. of spans =10 (3-span bending), 8 ( 2-span bending), 1.67 (3-span shear), 1.6 ( 2-span shear). The factor for two spans applies to vertical sheathing at 24 " spacing, the factor for 3 spans applies to all other situations
KD : Duration factor for wind = 1.15
mp : Bending strength from CSA O86 Tables 9.3A-C, where the value for 0º is used for horizontal sheathing and 90º for vertical sheathing
vpb : Planar shear in bending value from Tables 9.3A-C, where the value for 0º is used for horizontal sheathing and 90º for vertical sheathing
s : Stud spacing
Note that these values assume full-width plywood. For situations where the plywood is cut to a smaller dimension, 3 spans cannot be assumed and the designer must make the necessary adjustments.