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

200 Chapter Eight
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Moment of inertia, I = 0.199 in. 4
Rolling shear constant, Ib/Q = 7.187 in. 2
From Table 4-12 the indicated allowable stresses for Class I Plyform
will be:
Allowable bending stress, F b
= 1,930 lb per sq in.
Allowable rolling shear stress, F s
= 72 lb per sq in.
Modulus of elasticity, E = 1,650,000 lb per sq in.
The maximum pressure of the freshly placed concrete on the forms
will be 600 lb per sq ft. Consider a strip of Plyform 12 in. wide and 8 ft
long at the bottom of the forms. For the 12-in.-wide strip the value of
uniformly distributed load will be w = 600 lb per lin ft. The pressure on
the Plyform will occur over multiple supports; therefore, Beam 9 in
Table 5-2 will apply.
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Determine the spacing of studs based on bending of sheathing.
From Eq. (5-41), l b
= [120F b
S e
/w b
] 1/2
= [120(1,930)(0.455)/600] 1/2
= 13.2 in.
Determine the spacing of studs based on rolling shear of sheathing.
From Eq. (5-48), l s
= 20F s
(Ib/Q)/w s
= 20(72)(7.187)/600
= 17.2 in.
Determine the spacing of studs based on a maximum deflection
of l/360, but not greater than ¹⁄16 in.
From Eq. (5-57a), l d
= [1,743EI/360w d
] 1/3 for ∆=l/360
= [1,743(1,650,000)(0.199)/360(600)] 1/3
= 13.8 in.
From Eq. (5-57b), l d
= [1,743EI/16w d
] 1/4 for ∆=¹⁄16 in.
= [1,743(1,650,000)(0.199)/16(600)] 1/4
= 15.6 in.
Summary for ¾-in. Plyform Sheathing
For bending, the maximum spacing of studs = 13.2 in.
For shear, the maximum spacing of studs = 17.2 in.
For deflection, the maximum spacing of studs = 13.8 in.
The maximum span length of the ¾-in. Plyform sheathing is
governed by bending at 13.2 in. For constructability, choose 12 in.
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