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

62 Chapter Four
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Plyform Plyform Structural
Item
Class I Class II I Plyform
Bending stress, lb/in. 2 F b
1,930 1,330 1,930
Rolling shear stress, F s
72 72 102
lb/in. 2
Modulus of Elasticity— E 1,650,000 1,430,000 1,650,000
(psi, adjusted, use
for bending deflection
calculation)
Modulus of Elasticity—
(lb/in. 2 , unadjusted,
use for shear deflection
calculation)
E e
1,500,000 1,300,000 1,500,000
Note:
1. Courtesy, APA—The Engineered Wood Association.
TABLE 4-12
Allowable Stresses for Plyform, lb per sq in.
ww.EasyEngineering.n
spans up to 16 in. and two spans for 20 and 24 in. These are general
rules as recommended by the APA. For specific applications, other
span continuity relations may apply.
There are many combinations of frame spacings and plywood
thicknesses that may meet the structural requirements for a particular
job. However, it is recommended that only one thickness of plywood
be used, and then the frame spacing varied for the different
pressures. Plyform can be manufactured in various thicknesses, but
it is good practice to base design on the most commonly available
thicknesses.
Allowable Pressure Based on Fiber Stress in Bending
For pressure controlled by bending stress, use Eqs. (4-1) and (4-2).
w b
= 96F b
S e
/(l b
) 2 for one or two spans (4-1)
w b
= 120F b
S e
/(l b
) 2 for three or more spans (4-2)
where w b
= uniform pressure causing bending, lb per sq ft
F b
= allowable bending stress in plywood, lb per sq in.
S e
= effective section modulus of a plywood strip 12 in. wide,
in. 3 /ft
l b
= length of span, center to center of supports, in.
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