Figure 7-18.-Precast panels in position.
are called PURLINS. The cross sections of these
beams are shaped like a T or an I. The ones with the
inverted T-sections are usually used in composite
construction where they support cast-in- place floor
or roof slabs.
BEAMS and GIRDERS are terms usually applied
to the same members, but the one with the longer
span should be referred to as the girder. Beams and
girders may be conventional precast design or
prestressed. Most of the beams will be I-shaped
unless the ends are rectangular. The T-shaped ones
can also be used.
Precast concrete COLUMNS may be solid or
hollow. If the hollow type is desired, heavy card-board
tubing should be used to form the core. A looped rod
is cast in the column footing and projects upward into
the hollow core to help hold the column upright. An
opening should be left in the side of the column so
that the column core can be filled with grout. This
causes the looped rod to become embedded to form an
anchor. The opening is dry packed.
Advantages of Precast Concrete
Precast concrete has the greatest advantage
when identical members are to be cast because the
same forms can be used several times. Some other
advantages are listed below.
Control of the quality of concrete.
Smoother surfaces, and plastering is not
Less storage space is needed.
Concrete member can be cast under all weather
Better protection for curing.
Weather conditions do not affect erection.
Faster erection time.