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

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Forms for Walls 215
ties, considering the allowable unit stresses in bending and shear, and
the permissible deflection for the wales, whichever limits the spacing.
See Table 5-3 for the equations to calculate the allowable span length.
A check must also be made for the bearing stress between the stud
and the wale.
5. Select form ties that will safely withstand the forces transmitted
to them by the wales. An alternate method is to select the form ties,
then to determine the maximum safe spacing along the wales, checking
to be certain that this spacing does not exceed that deter-mined in
step 4.
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Physical Properties and Allowable Stresses for Lumber
For clarity in illustrating the design of wall forms, the physical properties
and allowable stresses of S4S dimension lumber and Plyform
are reproduced here from Chapter 4. These values are shown in
Tables 9-1 through 9-4. Also, the definition of terms and the summary
of equations from Chapter 5 for the design of formwork are repeated
for clarity (see Tables 9-5 and 9-6).
Table 9-2 gives the tabulated design values of Southern Pine
lumber for normal load duration and dry service conditions (<19%
moisture content). The values tabulated in Table 9-2 are only for
Southern Pine. If other species and grades are used for formwork,
the tabulated stresses should be adjusted to conform to the kind of
lumber used.
Physical Properties and Allowable Stresses for Plyform
Table 9-3 provides the physical properties of Plyform. These properties
are for a 12-in. width of plywood. The allowable stresses for Plyform
are shown in Table 9-4.
Table of Equations for Calculating Allowable Span Lengths
for Wood Beams and Plywood Sheathing
Table 9-5 provides a summary of the equations used for calculating
the allowable span lengths for wood beams with uniformly distributed
loads, and Table 9-6 provides the equations for calculating the
allowable span lengths of Plyform sheathing for uniformly distributed
concrete pressure. The allowable stresses for bending F b
and
horizontal shear F v
are in lb per sq in. The unit for allowable span
length is inches. The units for physical properties are defined in the
previous pages of this chapter.
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