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

300 Chapter Ten
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Determine the minimum length of z in Figure 10-5 to provide
adequate area in shear between the bolt and the end of the yoke. The
area in shear is z times twice the width of member A,
A = (z)(2)(3.5)
= 7z
The required area, based on an allowable shear stress of 237 lb per
sq in. is
A = (600 lb)/(237 lb per sq in.)
= 2.53 sq in.
Equating the two areas A and solving for z gives:
7z = 2.53
z = 2.53/7
= 0.36 in.
However, the length of z should be at least 3 in. to eliminate the
possibility of splitting a member.
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Steel Column Clamps with Wedges
Figure 10-6 illustrates a steel column clamp for forming square or
rectangular columns. One set of clamps consists of two hinged units,
which permits fast assembly with positive locking attachments by
steel wedges. This clamp is available in a 36-in. and a 48-in. overall
side bar length and can be adjusted to any fraction of an inch. The
36-in. size clamp with flat 2 × 4 s can form up to a 24-in.-square column.
The 48-in. size with the same lumber will form a 36-in.-square
column. Both clamps will form rectangular columns, ranging from 8 to
24 in. for the smaller size clamps and from 12 to 36 in. for the larger
size clamps.
Steel wedges are used to attach and secure the column clamps.
The clamps automatically square the column as the wedge is tightened.
To prevent twisting of the column forms, the clamps should be
alternated 90 ° as shown in Figure 10-6.
Column forms are often made with ¾-in.-thick Plyform and
either 2 × 4 s or 2 × 6 s placed flat against the outside of the Plyform.
The spacing of column clamps is governed by deflection of
both the lumber and the clamps. Table 10-4 provides clamp spacings
for this steel column clamp. Column clamp deflection is limited
to l/270 and a concrete temperature of 70 ° F. The spacings
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