are placed on chairs and tied as needed. Reinforcement
should be as near the center of the panel as possible.
Reinforcing bars are run through the side forms of the
panel. When welded wire fabric or expanded wire
mesh is used, dowel bars are used to tie the panels and
their vertical supports together. Additional
reinforcement is generally needed around openings.
The panel is picked up or tilted by the use of
PICKUP INSERTS. These inserts are tied into the
reinforcement. As the panel is raised into its vertical
position, maximum stress will occur; therefore, the
location and number of pickup inserts are extremely
important. Some engineering manuals provide
information on inserts, their locations, and capacities.
TILT-UP PANEL FOUNDATIONS. A n
economical and widely used method to support tilt-up
panels is a simple pad footing. The floor slab, which
is constructed first, is NOT poured to the perimeter of
the building to permit excavating and pouring the
footings. After the panel is placed on the footing, the
floor slab is completed. It may be connected directly
to the outside wall panel or a trench may be left to run
mechanical, electrical, or plumbing lines.
Another method that is commonly used, as an
alternative, is to set the panels on a grade beam or a
foundation wall at floor level. Regardless of the type
of footing, the panel should be set into a mortar bed to
ensure a good bond between the foundation wall and
PANEL CONNECTIONS. The panels may be
tied together in a variety of ways. The location and the
use of the structure will dictate what method can or can
NOT be used. The strongest method is a cast-in-place
column with the panel-reinforcing steel tied into the
column. However, this does NOT allow for expansion
and contraction. It may be preferable to tie only the
corner panels to the columns and allow the remaining
panels to move.
A variety of other methods of connecting the
panels are also used. A BUTTED connection, using
grout or a gasket, can be used if the wall does NOT
contribute any structural strength to the structure.
Steel columns are welded to steel angles or plates
secured in the wall panel. Precast columns can also be
used. Steel angles or plates are secured in both the
columns and plate and welded together to secure the
When panel connections that do not actually hold
the panels in place are used, the panels are generally
welded to the foundation and to the roof by using steel
angles or plates. All connections must provide
waterproof joints. This is accomplished by the use of
expansion joint material.
Precasting is done either in central prefabrication
plants or on-site prefabrication plants, depending upon
the product and its application. On-site or temporary
prefabrication plants are generally more suitable for
military operations. These plants are without roofing
and, therefore, are subject to weather and climate
considerations. The prefabrication yard is laid out to
suit the type and quantity of members to be processed.
It must be on firm, level ground, providing ample
working space and access routes. Bridge T-beams,
reinforced concrete arches, end walls, and concrete
logs are typical members produced at these plants. A
schematic layout of a prefabrication yard suitable for
producing such members is shown in figure 3-21. A
prefabrication unit of this size can be expected to
produce approximately 6,000 square feet of precast
walls per day. The output will vary according to the
experience of the personnel, equipment capabilities,
and product requirements.
CASTING. The casting surface is very
important in making precast concrete panels. In this
section, we will cover two common types: earth and
concrete. Regardless of which method you use,
however, a slab must be cast in a location that will
permit easy removal and handling.
Castings can be made directly on the ground with
cement poured into forms. These earth surfaces are
economical but only last for a couple of concrete
pours. Concrete surfaces, since they can be reused
repeatedly, are more practical.
When building casting surfaces, you should keep
the following points in mind:
The subbase should be level and properly
The slab should be at least 6 inches thick and
made of 3,000 psi or higher reinforced concrete.
Large aggregate, 2 1/2 inches to 3 inches
maximum, may be used in the casting slabs.
If pipes or other utilities are to be extended up
through the casting slab at a later date, they
should be stopped below the surface and the
openings temporarily closed. For wood, cork, or
plastic plugs, fill almost to the surface with sand