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

246 Chapter Nine
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1 in. thick, are used for sheathing. The template rings are sawed to the
correct curvatures from 2-in.-thick lumber. If planks as wide as 12 in.
in nominal width are used, it is possible to obtain an inside and outside
ring segment from each plank. The outside segments are sawed
to the correct curvature. The inside segments may be resawed to the
correct inside curvature, or if a slight deviation from a true circle is
not objectionable, they need not be resawed. The larger the radius,
the less there will be a need to resaw the inside segment.
The vertical wales are usually double 2 × 4 planks. The inside
form should be erected first and securely braced in the correct position.
Then the outside form is erected, and the form ties are secured
on both sides.
The equations and procedures presented in Chapter 5 may be
used to determine the maximum spacing of the template rings, wales,
and form ties. As indicated in Figure 9-12, the spacing of the rings
may be increased for the upper portion of the wall, corresponding to
the reduction in the pressure from the concrete.
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Form Ties
As illustrated in Figure 9-1, form ties are used with forms for walls
to hold the two sides against the pressure of the concrete. In addition
to resisting the pressure from the concrete, some ties are designed to
serve as form spreaders. Many types and sizes are available.
The maximum spacing of ties may be limited by the strength of
the ties, the maximum safe span for the wales, or the maximum
safe span of the studs in the event wales are not used. The manufacturers
of ties specify the safe working load for each size and type
manufactured.
It is frequently specified that ties must be removed from a concrete
wall or that portions must be removed to a specified depth and the
holes filled with cement mortar to eliminate the possibility of rust
stains appearing later, or to prevent water from seeping through a
wall around the ties. Smooth-rod ties can be pulled from the wall after
the forms are removed. Other methods, illustrated hereafter, are used
to permit the removal of portions of the ties within the concrete.
Snap Ties
As illustrated in Figure 9-13, these ties are made from a single rod
equipped with an enlarged button or a loop at each end to permit the
use of suitable tie holders. A portion of the rod in the concrete is
crimped to prevent it from turning when the ends are removed by
being bent and twisted. Ties can be furnished to break off at any
desired depth within the concrete. They are available with washers or
with tapered plastic cones attached to permit them to serve as form
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