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

136 Chapter Five
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6. Dry condition for wood, <19% moisture content
7. Deflection limited to l/360, but not greater than ¹⁄16 in.
8. All form lumber will be 2-in.-thick S4S lumber, No. 2 grade
Southern Pine with no splits, (Table 4-2)
9. Short load-duration, less than 7 days
10. Sheathing will be 7 ⁄8-in. plywood from Group I species
(Table 4-9), with a level S-2 stress rating, (Tables 4-9 and 4-10)
The design will be performed in the following sequence: determine
the maximum lateral pressure of the concrete on the wall forms
based on temperature and rate of filling the forms; determine the
spacing of studs based on the strength and deflection of plywood
sheathing; determine the spacing of wales based on the strength and
deflection of studs; check the bearing strength between studs and
wales; determine the span length of wales between ties based on the
strength and deflection of wales; and determine the required strength
of the form ties. Figure 5-14 illustrates the span lengths and spacing
of the components of the wall form. Tables 5-3 and 5-4 provide the
equations that are necessary to design the wall forms.
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Lateral Pressure of Concrete on Forms
From Table 3-3, or from Eq. (3-2), the maximum lateral pressure of
concrete against the wall forms will be 825 lb per sq ft. Therefore, a
1-ft-wide strip of plywood would have a uniformly distributed load
of 825 lb per lin ft.
Plywood Sheathing to Resist Pressure from Concrete
Because the type and thickness of plywood have already been chosen,
it is necessary to determine the allowable span length of the
plywood, the distance between studs, such that the bending stress,
shear stress, and deflection of the plywood will be within allowable
limits. Table 4-9 provides the section properties for the 7 ⁄8-in.-thick
plywood selected for the design. The plywood will be placed with the
face grain across the supporting studs. Therefore, the properties for
stress applied parallel to face grain will apply. Following are the
physical properties for a 1-ft-wide strip of the 7 ⁄8-in.-thick plywood:
Approximate weight = 2.6 lb per sq ft
Effective thickness for shear, t = 0.586 in.
Cross-sectional area, A = 2.942 in. 2
Moment of inertia, I = 0.278 in. 4
Effective section modulus, S e
= 0.515 in. 3
Rolling shear constant, Ib/Q = 8.050 in. 2
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