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

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Forms for Walls 223
FIGURE 9-3 Distribution of concrete pressure for Example 9-1.
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Effective section modulus, S e
= 0.455 in. 3
Rolling shear constant, Ib/Q = 7.187 in. 2
Table 9-4 gives values of bending stress, shear stress, and modulus
of elasticity for Plyform Class I as follows:
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 for shear deflection, E e
= 1,500,000 lb per sq in.
Modulus of elasticity for bending deflection, E = 1,650,000 lb per
sq in.
Bending Stress in Plywood Sheathing
Because the Plyform will be installed over multiple supports, three or
more, Eq. (5-41) from Table 9-6 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(1,930)(0.455)/(713)] 1/2
= 12.1 in.
Rolling Shear Stress in Plywood Sheathing
The allowable span length of the plywood based on rolling shear
stress can be calculated using Eq. (5-48) from Table 9-6:
From Eq. (5-48): l s
= 20F s
(Ib/Q)/w s
= 20(72)(7.187)/713
= 14.5 in.
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