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

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Design of Wood Members for Formwork 143
wale will be 825 lb per sq ft multiplied by 2.0 ft, or 1,650 lb per lin ft.
The maximum spacing of the ties based on the strength of a 3,000 lb
safe working load tie is as follows:
l = (3,000 lb)/(1,650 lb per ft) = 1.8 ft.
l = 21.6 in.
For a 3,000 lb tie, the spacing must not exceed 21.6 in. For this
design, 4,000-lb ties will be used and placed at 24 in. center to center,
because the 24-in. spacing is convenient for layout and ease of
construction.
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Design Summary of Forms for Concrete Wall
The allowable stresses and deflection criteria used in the design are
based on the following lumber values.
For the 2 × 4 S4S No. 2 grade Southern Pine with no splits:
Allowable bending stress = 1,875 lb per sq in.
Allowable shear stress = 218 lb per sq in.
Modulus of elasticity = 1,600,000 lb per sq in.
Permissible deflection less than l/360, but not greater than
¹⁄16 in.
For the ¾-in.-thick plywood from Group I species with S-1 stress
rating:
Allowable bending stress = 2,062 lb per sq in.
Allowable shear stress = 66 lb per sq in.
Modulus of elasticity = 1,800,000 lb per sq in.
Permissible deflection less than l/360, but not greater than
¹⁄16 in.
The forms for the concrete wall should be built to the following
conditions:
Item
Sheathing
Studs
Wales
Form ties
Nominal size and spacing
7⁄8-in.-thick plywood
2 × 4 S4S at 12 in. on centers
double 2 × 4 S4S at 24 in. on centers
4,000-lb capacity at 24 in.
Figure 5-15 summarizes the design, including the size and
spacing of studs, wales, and form ties.
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