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

288 Chapter Ten
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For shear, l = 192F v
bd/15w + 2d
= 192(225)(12)(1.5)/15(900) + 2(1.5)
= 60.6 in.
For deflection, l = [1,743EI/360w] 1/3 for ∆ = l/360
= [(1,743)(1,600,000)(3.375)/360(900)] 1/3
= 30.7 in.
For deflection, l = [1,743EI/16 ³⁄16w] 1/4 for ∆ = ¹⁄16 in.
= [1,743(1,600,000)(0.3.375)/16(900)] 1/4
= 28.4 in.
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For this 2-in. S4S sheathing, the maximum permissible span length
is 25.9 in., governed by bending. Therefore, the spacing of the column
clamps should not exceed this amount.
For this design a 25-in. spacing of clamps can be used. The column
clamps or yokes must be strong enough to resist the loads transmitted
to them by the sheathing. The design of yokes is discussed
later in this chapter.
Table 10-1 shows the maximum span lengths for the S4S lumber,
laid flat in the vertical direction, to carry the entire pressure in the vertical
direction between column clamps. These span lengths are based on
using clamps or yokes that are strong enough to resist the loads transmitted
to them by the sheathing.
Support spacings shown in Table 10-1 are calculated using
Eqs. (10-3) to (10-6) for the concrete pressures and allowable stresses
shown at the bottom of the table. The spacings are the maximum as
governed by bending, shear, or deflection.
Plywood Sheathing with Vertical Wood Battens
for Column Forms
A common practice for fabricating forms is to place vertical battens of
2 × 4 dimension lumber on the outside of the plywood sheathing, as
illustrated in Figure 10-2. The 2 × 4 s are placed flat against the plywood
and act as studs, similar to the design of wall forms, as discussed
in Chapter 9. For some job conditions, 2 × 6 battens are used in
lieu of 2 × 4 battens.
The concrete pressure acts against the plywood panel, which
must transfer the pressure in a horizontal direction to the adjacent
vertical wood battens. The vertical wood battens must then transfer
the loads, transferred to them from the plywood sheathing, in a vertical
direction between column clamps.
The plywood must have sufficient strength and rigidity to transfer
the concrete pressure between the wood battens. Equations (10-7) to (10-10)
can be used to determine the maximum distance between the wood battens,
which is equivalent to the maximum span length of plywood.
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