Prestressed

1. 
Abstract—pre-stressed concrete can be considered as one of the
greatest innovations in the field of concrete construction. This
innovation lead to replace the conventional method of concrete
construction (reinforced concrete) with lots of merits mainly in
terms of possibilities of making long span structures, ability to
resist impact, high live load carrying capacity and its tensile stress
free character. Pre-stressedconcrete members are pre-casted and
are helpful in decreasing the time for completion of a work. This
method is mainly used for large scale projects such as metro,
flyovers where completion time is very crucial. This in turn leads
to more effective structural members andeffective use of resources
in a way which is less harmful to the environment.
Index Terms—pre stress concrete, off site construction
I. INTRODUCTION
Used high tensile steelwires, 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-stressedconcrete.
Eugene Freyssinet (France)
II. WHAT IS PRE-STRESSED CONCRETE.
Pre-stressed concrete is a form of reinforced concrete that
builds in compressive stresses during construction to oppose
those found when in use. So it works on an application of an
initial load on the structure so as to enable the structure to
counteract the stresses arising during its service period.
This combination of steel and concrete that takes
advantages of the strengths of each materials.
A. Concept of pre-stressing.
The concept of pre stressing was invented years ago
when metal brands were wound around wooden pieces to
form barrels.
The metal bands were tighten under tensile stress which
creates compression between the staves allowing them to resist
internal liquid pressure.
B. Principles 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.
Possibilities of Pre-stressed concrete in
construction (April 2016)
Vivek Paul, SEM VI student, KMEA College of Architecture
Pre-stressed concrete is basically concrete in which internal
stresses ofa suitable magnitude and distribution are introduced
so that the stresses resulting from the external loads are
counteracted to a desired degree.
1938 Hoyer, E., (Germany)
Developed ‘long line’ pre-tensioning method.
1940 Magnel, G., (Belgium)
Developed an anchoring systemfor post-tensioning,
using flat wedges.

2.  It is then possible to treat concrete as an elastic
material.
 The concrete can be visualized to have two
compressive force
i. Internal pre-stressing force.
ii. External forces
These two forces must counteract
Each other.
III. MATERIALS USED FOR PRE-STRESSING.
Pre-stressed concrete was started to be used in building frames,
parking structures,stadiums,railway sleepers,transmission line
poles and other types of structures and elements.
Materials for pre-stress concrete member
1. Cement,
2. Concrete,
3. Steel.
1. Cement:
Ordinary Portland cement,
Portland slag cement,
Rapid hardening Portland cement,
High strength ordinary Portland cement.
2. 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.
3. Steel:
High tensile steel,tendons,strands.In pre-stress concrete
high tensile steel with tensile strength around 2000MPa.
According to IS: 1343-1980 pre-stress concrete is design
Pre-stressing wire is a single
Unit made of steel.
IV. TYPES OF PRE-STRESSING.
1. 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 initial length but the concrete resists it
through the bond between them, thus, compression force is
induced in concrete. Pretension is usually done with precast
members
2. Post tensioning.
In post tension,the tendons are tensioned after the concrete has
hardened. Commonly, metal or plastic ducts are placed inside
the concrete before casting. After the concrete hardened and
had enough strength, the tendons was placed inside the duct,
stressed and anchored against concrete. Grout may be injected
into the duct later. This can either done in factories or in site
itself.
Two, three or seven wires are wound to form a pre-
stressing strand.
A group of strands or
wires are wound to form
a pre-stressing tendon.
A tendon can be made up
of a single steel bar. The
diameter of a bar is much
larger than that of a wire.

3. V. COMPARISON BETWEEN PRE-TENSIONED AND POST
TENSIONED.
VI. ADVANTAGES OF PRE-STRESSED CONCRETE.
 Factory products are possible.
 Long span structureare possibleso that saving of wt is
significant & thus it become economical.
 Pre-stressed member are tested before use.
 Dead load are get counter balanced by eccentric pre-
stressing
 It has high ability to resist the impact.
 It has high fatigue resistance.
 It has high live load carrying capacity.
 It free from cracks from service loads and enable entire
section to take part in resisting moments.
 Member are free from the tensile stresses.
VII. DISADVANTAGES OF PRE-STRESSED CONCRETE.
 Required skilled builders & experienced engineers.
 Initial equipment cost is very high.
 Availability of experienced engineers is less.
 Required complicated formwork.
 It requires high strength concrete & steel.
 Pre-stressed concrete is less fire resistant.
VIII. ADVANTAGESOF PRE-STRESSED CONCRETE.
 Bridges
 Slabs in buildings
 Water Tank
 Concrete Pile
 Thin Shell Structures
 Offshore Platform
 Nuclear Power Plant
 Repair and Rehabilitations