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

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Properties of Form Material 63
Allowable Pressure Based on Bending Deflection
For pressure controlled by bending deflection, use Eqs. (4-3) and (4-4).
w d
= 2220EI∆ b
/(l s
) 4 for two spans (4-3)
w d
= 1743EI∆ b
/(l s
) 4 for three or more spans (4-4)
where ∆ b
= permissible deflection of plywood, in.
w d
= uniform pressure causing bending deflection, lb per
sq ft
l s
= clear span of plywood plus ¼ in. for 2-in. supports, and
clear span plus 5 ⁄8 in. for 4-in. supports, in.
E = adjusted modulus of elasticity of plywood, lb per
sq in.
I = moment of inertia of a plywood strip 12 in. wide, in. 4 /ft
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Allowable Pressure Based on Shear Stress
For pressure controlled by shear stresses, use Eqs. (4-5) and (4-6).
w s
= 19.2F s
(Ib/Q)/l s
for two spans (4-5)
w s
= 20F s
(Ib/Q)/l s
for three spans (4-6)
where w s
= uniform load on plywood causing shear, lb per sq ft
F s
= allowable rolling shear stress, lb per sq in.
Ib/Q = rolling shear constant, in. 2 /ft of width
l s
= clear span between supports, in.
Allowable Pressure Based on Shear Deflection
For pressure controlled by shear deflection, use Eq. (4-7).
∆ s
= w s
Ct 2 (l s
) 2 /1270E e
I (4-7)
where ∆ s
= permissible deflection of the plywood, in.
w s
= uniform load causing shear deflection, lb per sq ft
C = a constant, equal to 120 for the face grain of plywood
Perpendicular to the supports, and equal to 60 for the face
grain of the plywood parallel to supports
t = thickness of plywood, in.
E e
= modulus of elasticity of the plywood, unadjusted for shear
deflection, lb per sq in.
I = moment of inertia of a plywood strip 12 in. wide, in. 4 /ft
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