This document discusses pre-stressed concrete and provides details on: 1. The different types of pre-stressing including pre-tensioning and post-tensioning. Pre-tensioning involves tensioning before concrete casting while post-tensioning tensions after casting. 2. The forms of prestressing steel used including wires, strands, tendons, and cables. 3. The common systems for pre-tensioning and post-tensioning including Freyssinet, Magnel, Gifford-Udall, and Lee-McCall systems. 4. The sources of losses in prestress over time including elastic shortening, friction, anchorage slip, creep of concrete, shrink

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2. Submitted to –
Er. Rachana kaushik
Submitted By –
Anoop ,Pawan, Ajay,
Arjun, Sunil kumar
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Pre Stress Concrete
Pre Stress

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Compression (C) Tension (T)
Stones, Bricks Steel
Steel bars, wires
Reinforced
Concrete
Prestressed
Concrete
High Strength
Steel
High Strength
Concrete
Combination
Concrete
Combination
Development Process of Pre Stress Concret

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Types Of Pre Stress
1. Externally or internally prestressing
2. Circular and linear prestressing
3. Pre tensioning and Post tensioning
4. Partially or fully Prestressing

7. Types Of Tensioning
Pre Tensioning
Post Tensioning
Tensioning Before concrete Casting Tensioning After concrete Casting
1. Pre Tensioning 2. Post Tensioning
Exp:- Electric pole , Railway Sleeper Exp:- Box Girder

8. Devices use on Pre stressing System
Pre Tensioning
Devices
Post Tensioning
Devices

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Forms of Prestressing Steel
Wires
Prestressing wire is a single unit made of steel. Strands Two,
three or seven wires are wound to form a prestressing strand.
Tendon
A group of strands or wires are wound to form a
prestressing tendon.
Cable
A group of tendons form a prestressing cable.
Bars
A tendon can be made up of a single steel bar. The
diameter of a bar is much larger than that of a wire.
Strand
A few wires are spun together in a helical form to form a
prestressing strand.

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Systems of
post tensioning
Systems of
pre tensioning
1. Freyssinet system
2. Magnel system
3. Gifford-Udall system
4. Lee-McCall system
1. Hoyer system
Systems of pre stressing

11. Freyssinet system Magnel system
Gifford-Udall system Lee-McCall system
Systems of Post Tensioning

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13. Step 1. Tendons are provided in mould
Step 2. Tendons are stressed to about 70%
of their ultimate strength.
Step 3. Concrete is cast into the beam mould
Step 4. Concrete has cured and
the stressing force is released.

14. Step 1. Cable ducts and reinforcement are positioned
in the beam mould
Step 2. Concrete is cast into the beam mould
Step 3. Tendons are threaded through the cable ducts
Step 4. Wedges are inserted into the end anchorages and
the tensioning force on the tendons is released

15. Manufacturing Process of Railway Sleepers
1. Prepare the Tendons
2. Mould oiling
3. Tendons are Laying in the Mould

16. Manufacturing Process of Railway Sleepers
4. Tendons are starched by Jack
5. Concreting in the Mould
6. Tendons are releasing

17. Manufacturing Process of Railway Sleepers
7. Concrete sleeper are removed
in the mould
8. Curing
9. Storage and Ready to Placing

18. Losses of Prestress Concrete

19. When the tendons are cut and the prestressing force is
transferred to the member, concrete undergoes
immediate shortening due to prestress.
Loss range 3 to 6 % .
1. Elastic Shortening
Length after elastic shortening
P0
Elastic shortening of a pre-tensioned axial member

20. 2. Friction
The friction generated at the interface of concrete and steel
during the stretching of a curved tendon in a post tensioned
member, leads to a drop in the pre-stress along the member
from the stretching end.
Not more than 2 %
Duct
jackAnchorage

21. 3. Anchorage slip
In a post-tensioned member, when the pre-stress is transferred to
the concrete, the wedges slip through a little distance before
they get properly seated in the conical space .
Loss in slip in wire – 2 to 3 mm
Loss in slip in heavy strand – 5mm
Prestressing Bed

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4. Creep of Concrete
Creep of concrete is defined as the increase in
deformation with time under constant load. Due to the
creep of concrete, the prestress in the tendon is reduced
with time.
Creep losses 5 to 10 %
Age of Loading
7 Days
28 Days
1 Year
Creep Coefficient
2.2
1.6
1.0

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The shrinkage of concrete is defined as the contraction
due to loss of moisture. Due to the shrinkage of concrete,
the prestress in the tendon is reduced with time.
Lossess for pre tensioned Work - 4 to 6 %
Lossess for post tensioned work – 3 to 4 %
5. Shrinkage of Concrete

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Relaxation of steel is defined as the decrease in stress
with time under constant strain. Due to the relaxation of
steel, the prestress in the tendon is reduced with time.
Losses of relaxation in stress in steel – 2 to 8 %
6. Relaxation of stress in Steel

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