Introduction
of prestressedconcrete piles
has reduced the weight of precast pilesproviding
a advantage of easy handling. The weight of very large pile is
reduced by casting 200 mm to 300 mm diameter fibre tubes insidethe piles
at the time of concreting.
In casting prestressed concrete piles, the pretensioning cables
required for each piles are subjected to the required pull (tension) in the
casting bed. The fibre tube for forming void in the pile (if needed) is
securely held in position in side the form work and the piles reinforced with
the pre-tensioned cables are concreted in a row. The casting bed can be
made to accommodate 2 to 5 lines of piles 120 to 150 metre long. Prestressed piles
are provided with lifting hooks at 1/5 th of the pile length from
each end.
In general, square prestressed concrete piles of length 50 times the
thickness can be handled with a single point pick-up and up to 60
times the thickness with two point pick-up. Piles 500 mm square and
smaller are usually cast solid, whereas pile above 500 mm square may be cast
with 200 mm to 300 mm diameter cored hole(void).
On account of their reduced
weight, prestressed concrete piles have definitehandling
advantage over precast piles and as such they are getting increasingly popular
these days. When compared with reinforced concrete piles, prestressedpiles
have proved to be extremely durable in tidal zones and
for harbour installations, where unsupported lengths of the piles becomes
considerable. Their load carrying capacity is high and they are capable of
resisting uplift forces and combined moments. in addition, they can withstand
extremely hard driving stresses which may be far more than that which a
conventional type of reinforced concrete pile can bear.
