Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

138 Chapter Five
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Bending Stress in Plywood Sheathing
Because the plywood will be installed over multiple supports, three
or more, Eq. (5-41) can be used to determine the allowable span length
of the plywood based on bending.
From Eq. (5-41), l b
= [120F b
S e
/w b
] 1/2
= [120(2,062)(0.515)/(825)] 1/2
= 12.4 in.
Rolling Shear Stress in Plywood Sheathing
The allowable span length of the plywood based on rolling shear
stress can be calculated.
ww.EasyEngineering.n
From Eq. (5-48), l s
= 20F s
(Ib/Q)/w s
= 20(66)(8.050)/825
= 12.8 in.
Bending Deflection in Plywood Sheathing
For a maximum permissible deflection of l/360, but not greater
than ¹⁄16 in., and plywood with three or more spans, Eqs. (5-57a)
and (5-57b) can be used to calculate the allowable span lengths for
bending deflection.
From Eq. (5-57a), l d
= [1,743EI/360w d
] 1/3 for ∆=l/360
= [1,743(1,800,000)(0.278)/360(825)] 1/3
= 14.3 in.
From Eq. (5-57b), l d
= [1,743EI/16w d
] 1/4 for ∆ =¹⁄16 in.
= [1,743(1,800,000)(0.278)/16(825)] 1/4
= 16.0 in.
Summary for the ¾-in.-Thick Plywood Sheathing
For bending, the maximum span length of the plywood = 12.4 in.
For shear, the maximum span length of the plywood = 12.8 in.
For deflection, the maximum span length of the plywood = 16.0 in.
For this design, bending controls the maximum span length of
the plywood sheathing. The studs that support the plywood must
be placed at a spacing that is no greater than 12.4 in. For uniformity
and constructability, choose a maximum stud spacing of
12.0 in., center to center.
Studs for Support of Plywood
The studs support the plywood and the wales must support the studs.
Therefore, the maximum allowable spacing of wales will be governed
by the bending, shear, and deflection in the studs.
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