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

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Forms for Walls 229
Strength Required of Ties
Based on the strength of the wales in bending, shear, and deflection,
the wales must be supported every 24 in. by a tie. A tie must resist the
concrete pressure that acts over an area consisting of the spacing of
the wales and the span length of the wales, 24 in. by 24 in. The load
on a tie can be calculated as follows:
Area = 2.0 ft × 2.0 ft
= 4.0 sq ft.
Load on a tie = 713 lb per sq ft (4.0 sq ft)
= 2,852 lb
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To support a wale at every 24 in., the tie must have an allowable
load of 2,852 lb. Thus, a standard strength 3,000 lb working load tie is
adequate. The lateral pressure of freshly placed concrete on wall
forms is carried by the ties. However, the wall forms must be adequately
braced to resist any eccentric loads or lateral forces due to
wind. The minimum lateral force applied at the top of wall forms are
presented in Chapter 5 (refer to Table 5-7).
Results of the Design of the Forms for the Concrete Wall
The allowable stresses and deflection criteria used in the design are
based lumber on the following values:
For the 2 × 4 S4S No. 2 grade Southern Pine lumber:
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 Plyform Class I sheathing:
Allowable bending stress = 1,930 lb per sq in.
Allowable shear stress = 72 lb per sq in.
Modulus of elasticity = 1,650,000 lb per sq in.
Permissible deflection less than l/360, but not greater than ¹⁄16 in.
Figure 9-4 shows the design of the forms that should be built to
the following conditions:
Item
Sheathing
Studs
Wales
Form ties
Nominal Size and Spacing
¾-in. thick Plyform Class I
2 × 4 at 12 in. on centers
double 2 × 4 at 24 in. on centers
3,000 lb capacity at 24 in.
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