1. History
• Used high tensile steel wires, with ultimate
strength as high as 1725 MPa and yield stress
over 1240 MPa. In 1939, he developed conical
wedges for end anchorages for post- tensioning
and developed double-acting jacks. He is often
referred to as the Father of Pre-stressed
concrete.
• 1938 Hoyer(Germany) Developed long line pre
– tensioning method.
• 1940 Mangle, G.,(Belgium) Developed an
anchoring system for post-tensioning, using flat
wedges.
Eugene Freyssinet
(France)
2. In India, the application of pre-stressed concrete diversified over under the Assam
Rail Link Project . Among bridges, the Pamban Road Bridge at Rameshwaram,
Tamilndu, remains a classic example of the use of pre-stressed concrete girders.
• Ramban Road Bridge at Ramesh Aram, Tamilnadu
3. Reinforced concrete
Concrete is strong in compression and weak in tension
Steel is strong in tension
Reinforced concrete uses concrete to resist compression and to hold bars in position and
uses steel to resist tension
Tensile strength of concrete in neglected (i.e. Zero)
R.C beams allows crack under service load
4. • Pre-stressed concrete was started to be used in building frames, parking
structure, stadiums, railway sleepers, transmission line poles and other types of
structure and elements.
Materials for pre-stress concrete member
1. Cement
2. Concrete
3. Steel
Cement
Ordinary Portland cement
Portland slag cement
Rapid hardening Portland cement
High strength ordinary Portland cement.
5. Concrete
• Pre-stress concrete requires high strength concrete, which has high
compressive strength comparatively higher tensile strength than ordinary
concrete.
• the concrete is a material should be compose of gravels or crushed
stones, sand cement.
• In pre-stress concrete minimum grade of concrete M20
• Steel
• High tensile steel, tendons, strands.
• In pre-stress concrete high tensile steel with tensile strength around 2000MPa
• According to IS: 1343-1980 prestress concrete id design.
6. Pre-stressing is the application of an initial load on the
structure so as to enable the structure to counteract
the stresses arising during its service period.
• Per-stressed concrete is a form of reinforced concrete that builds in
compressive stresses during construction to oppose found when in
use.
in other words, it is combination of steel and concrete
that takes advantages of the strengths of each material.
7. Concept of pre- stressing :
• The metal bands were
tighten under tensile
stress which creates
compression between
the staves allowing
them to resist internal
liquid pressure
The concept of pre steering was
invented when metal brands were
wound around wooden pieces to
form barrels
8. Principle of pre-stressing
• Pre-stressing is a method in which compression force is applied to the
reinforced concrete section.
• The effect of pre-stressing is to reduce the tensile stress in the section
to the point till the tensile stress is below the cracking stress . Thus
the concrete does not crack.
• It is then possible to treat concrete as a elastic material.
• The concrete can be visualized to have tow compressive force.
• Internal pre-stressing force
• External forces
• The tow forces must counteract each other.
9. Forms of pre-stressing steel
• Wire
• Strands
• Tendons • Bars
Tow, three or seven wires are
wound to form a pre-stressing
strand.
A tendon can be made up
of a single steel bar. The
diameter of bar is much
larger than that of a wire
Pre-stressing wire is a single unit
made of steel
A group of strands or
wires are wound to
form a pre-stressing
tendon
10. Types of pre-stressing
• Pre- tensioning
• In pre-tension, the tendons are tensioned against some
abutments before the concrete is place. After the concrete
hardened, the tension force is released. The tendon tries to
shrink back to the bond between them, thus, compression
force is induced in concrete.
• Pre-tension is usually done with precast members.
