PILES AND PRE-STRESSING
Wood Piles
for moderately high
buildings on a compressible
soil saturated with water of
considerable depth
are made from straight
trunks of trees, not less than
5” in diameter at small end
for light buildings, or 8” for
heavy buildings
with an iron or steel cast
conical point about 5 in. in
dia., secured by a long
dowel with a ring around the
end of the pile.
driven by drop-hammer or steam-hammer, weights
from1,500 to 2,500 lb., with fall varying from 5 to
20 ft., the last blows being given with short falls
top of the pile protected from brooming by putting
on an iron ring, about 1 in. less in diameter than the
head of the pile, and from 2-1/2 to 3 in. wide by
5/8 in. thick
should not be spaced less than 2 to 3 ft. on centers;
When long piles are driven closer than 2 ft. on
centers, there is danger that they may force each
other up from their solid bed on bearing stratum.
Maximum allowable load on wood piles is usually
20 tons.
top of the piles should be cut off at or below the
low water mark, otherwise they will soon commence
to decay
Concrete Piles
advantageous for foundations on land where the
permanent ground water is at a considerable depth
are generally reinforced concrete and of two general
types: those molded in place and those molded before
driving
• spaced from 2’ – 6” to 4’
•extended at least 4” into the concrete of the footing,
and where a steel casing surrounds the pile, 3 to 4 in.
of concrete is required between the top of the piles
and the footing reinforcement
Cast-in-place Piles
Cast-in-placepiles may be formed by any of the
following methods:
a) A hollow cylindrical steel tube usually furnished with
a tight-fitting collapsible steel core or mandrel, is driven
into the soil. The core is then collapsed and removed, and
the steel shell filled with concrete. Thus there is a shell or
form for every pile, e.g. McArthur piles, Raymond piles
(this uses a No. 24 gauge shell in which a spiral of No. 3
wire is encased).
A steel tube is fitted at
the bottom with a driving
point and is driven into
the ground to the required
depth. Concrete is then
poured into the hole thus
formed as the steel tube is
gradually withdrawn. The
driving point may be
either a conical cast-iron
point that is left in place
or a hinged cutting-edge
called an alligator point
which opens as the tube is
withdrawn
Steel Piles
are concrete-filled steel
pipes made to bear on
rock or hard pan
are generally 10 to 18
inches in diameter,
having a thickness of
3/8 to 5/8 inches
Steel Piles
are driven in sections with a
steam-hammer and, as
additional sections are
required, these are attached
to the driven section by
means of a cast-iron or steel
internal sleeve and re-
driven.
When the pipe has reached
its bearing level it is cleaned
out by blowing or dug out
by means of augers or
similar tools and concreted
Composite Piles
are
combination timber
and concrete or steel
and concrete piles
Points of Discussion
Friction Pile
Drilled Pile
Bored piles
are cast-in-place, plain or reinforced concrete piers
formed by boring with a large auger or excavating by
hand a shaft in the earth to a suitable bearing stratum
and filling the shaft with concrete. For this reason they
are also referred to as drilled piles or piers.
Caisson Method
PRE-STRESSED CONCRETE
A pre-stressed concrete beam is a member so designed
and constructed that all of the stresses in the concrete
resulting from bending are compressive, none is tensile.
The name is derived from the fact that the stresses are
applied before the beam is loaded.
THERE ARE TWO METHODS OF PRESTRESSED
CONCRETE, NAMELY:
Pre-tensioning or bonded pre-stressing
Post-tensioning or unbounded pre-stressing
THERE ARE TWO METHODS OF PRESTRESSED
CONCRETE, NAMELY:
Pre-tensioning or bonded pre-stressing. In this method the
reinforcing steel is first pre-stressed and then the concrete is
poured. When the concrete has developed strength, the
stress in the steel is released.
THERE ARE TWO METHODS OF
PRESTRESSED CONCRETE,
NAMELY:
Post-tensioning or unbounded
pre-stressing. In this method,
tubes, conduits, or channels are
inserted in the concrete where
reinforcing steel is required.
After the concrete is
adequately cured, steel
reinforcement is inserted in the
tubes or channels, stretched to
the proper tension, and
anchored at the ends to put a
squeeze on the beam.
Tensioning is done with
hydraulic jacks.
