Prestressed concrete is a method for overcoming concrete's
natural weakness in tension.
In 1904, Freyssinet attempted to introduce permanent
acting forces in conc. to resist elastic forces under loads
and was named “Pre Stressing”.
It can be used to produce beams, floors or bridges with a
longer span than is practical with ordinary
Pre-stressing is a method in which compression force is
applied to the reinforced concrete section.
Pre-stressing tendons (generally of high tensile steel cable or
rods) are used to provide a clamping load which produces a
compressive stress that balances the tensile stress that the
concrete compression member would otherwise experience
due to a bending load.
This classification is based on the method by which the
prestressing force is generated.
Pre-stressed concrete refers to a
procedure whereby tensile rods
are put in place first and
tightened, followed by concrete
Compression can be applied
after pouring concrete using
bonds. They are tightened once
the concrete is dry
Main disadvantage is that a
cable can burst out of the slab, if
the anchoring system fails.
Even without a load, the
ordinary concrete beam
must carry its own
An upward force is
created which in effect
relieves the beam of
having to carry its own
There are two types of prestressed concrete.
Pre- tensioned concrete
Post tensioned concrete
Pre-tensioned concrete is cast
around already tensioned tendons.
This method produces a good
bond between the tendon and
concrete, which both protects the
tendon from corrosion and allows
for direct transfer of tension.
The cured concrete adheres and
bonds to the bars and when the
tension is released it is transferred
to the concrete as compression by
Post tensioning is a technique for reinforcing concrete.
Post-tensioning tendons, which are prestressing steel cables inside
plastic ducts or sleeves, are positioned in the forms before the
concrete is placed.
Afterwards, once the concrete has gained strength but before the
service loads are applied, the cables are pulled tight, or tensioned,
and anchored against the outer edges of the concrete.
They are classified into two types,
Bonded post tensioned concrete
Unbonded post tensioned concrete
Bonded post-tensioned concrete is the descriptive term
for a method of applying compression after pouring
concrete and the curing process (in situ).
The concrete is cast around a plastic, steel or
aluminium curved duct, to follow the area where
otherwise tension would occur in the concrete element.
Unbonded post-tensioned concrete differs from
bonded post-tensioning by providing each individual
cable permanent freedom of movement relative to the
To achieve this, each individual tendon is coated with a
grease (generally lithium based) and covered by a
plastic sheathing formed in an extrusion process.
Take full advantages of high strength concrete and
high strength steel
Need less materials
Smaller and lighter structure
Use the entire section to resist the load
Better corrosion resistance
Very effective for deflection control
Better shear resistance
Slabs in buildings
Thin shell structures
Nuclear power plant
Repair and rehabilitations
Thus, pre-stressed concrete increases the quality,
strength, span of the structure.
Since it is cost effective, it is used widely on recent