made to a depth of one half of the bar diameter and for
a length eight times the bar diameter.
The minimum clear distance between parallel bars
in beams, footings, walls, and floor slabs should either
be 1 inch (25.4 mm) or 1 1/3 times the largest size
aggregate particle in the concrete, whichever distance
is greater. In columns, the clear distance between
parallel bars should be not less than 1 1/2 times the bar
diameter or 1 1/2 times the maximum size of the coarse
aggregate. Always use the larger of the two.
The support for reinforcing steel in floor slabs is
shown in figure 7-24. The height of the slab bolster is
determined by the required concrete protective cover.
Concrete blocks made of sand-cement mortar can be
used in place of the slab bolster. Wood blocks should
never be used for this purpose. Highchairs (fig. 7-18)
can be obtained in heights up to 6 inches (15 cm).
When a height greater than 6 inches is required, make
the chair out of No. 0, soft, annealed iron wire. To hold
the bars firmly in position, you should tie the bars
together at frequent intervals where they cross with a
Steel for column ties may be assembled with the
verticals into cages by laying the vertical bars for one
side of the column horizontally across a couple of
sawhorses. The proper number of ties are slipped over
the bars, the remaining vertical bars are added, and
then the ties are spaced out as required by the placing
plans. All intersections are wired together to make the
assembly rigid so that it may be hoisted and set as a
unit. Figure 7-25 shows atypical column tie assembly.
After the column is raised, it is tied to the dowels
or reinforcing steel carried up from below. This holds
it firmly in position at the base. The column form is
erected and the reinforcing steel is tied to the column
form at 5-foot (4.5-m) intervals, as shown in figure
The use of metal supports to hold beam
reinforcing steel in position is shown in figure 7-8.
Note the position of the beam bolster. The stirrups are
tied to the main reinforcing steel with a snap tie.
Wherever possible you should assemble the stirrups
and main reinforcing steel outside the form and then
place the assembled unit in position. Precast concrete
blocks, as shown in figure 7-27, maybe substituted for
The horizontal and vertical bars are wired securely
to each other at sufficiently frequent intervals to make
a rigid mat. Tying is required at every second or third
intersection, depending upon the size and spacing of
bars, but with not less than three ties to any one bar,
and, in any case, not more than 4 to 6 feet apart in
Figure 7-24.Steel in place in a floor slab.