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

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Design of Wood Members for Formwork 137
FIGURE 5-14
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Span length and spacing of components of wall form.
For dry conditions, Table 4-10 indicates the allowable stresses for
the plywood of Group I species and S-2 stress rating for normal duration
of load. However, values for stresses are permitted to be increased
by 25% for short-duration load conditions, less than 7 days, as discussed
in Chapter 4 (Table 4-4). The 25% increase applies to bending
and shear but does not apply to the modulus of elasticity. Therefore,
the allowable stresses for the design of the plywood are obtained by
multiplying the tabulated stresses by 1.25 as follows:
Allowable bending stress, F b
= 1.25(1,650) = 2,062 lb per sq in.
Allowable rolling shear stress, F s
= 1.25 (53) = 66 lb per sq in.
Modulus of elasticity, E = 1,800,000 lb per sq in.
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