Prestressed concrete is a method for overcoming
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Prestressed concrete is a method for overcoming concrete 's natural weakness in tension PowerPoint PPT Presentation


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Prestressed concrete is a method for overcoming concrete 's natural weakness in tension. It can be used to produce beams , floors or bridges with a longer span than is practical with ordinary reinforced concrete.

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Prestressed concrete is a method for overcoming concrete 's natural weakness in tension

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Prestressed concrete is a method for overcoming concrete s natural weakness in tension

Prestressed concrete is a method for overcoming concrete's

natural weakness in tension

It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete

Prestressing tendons (generally of high tensilesteelcable or rods) are used

Prestressing can be accomplished in three ways:

Pre-tensioned concrete

Bonded or unbonded post-tensioned concrete.

Precompression (mostly, with the own weight of a structure)


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

Pre-tensioned concrete is cast around already tensioned tendons

This method produces a good bond between the tendon and concrete

This protects the tendon from corrosion and allows for direct transfer of tension

It requires stout anchoring points between which the tendon is to be stretched and the tendons are usually in a straight line.

Pre-tensioned elements may be balcony elements, lintels, floor slabs, beams or foundation piles.


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

Precast prestressed structures


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

prestressed Dome structures


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

Naturally precompressed

exterior wall of Colosseum, Rome


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

post-tensioned concrete

Bonded post-tensioned concrete

Unbonded post-tensioned concrete

Method of applying compression after pouring concrete and the curing process

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.

A set of tendons are fished through the duct and the concrete is poured.

Once the concrete has hardened, the tendons are tensioned by hydraulicjacks

When the tendons have stretched sufficiently, according to the design specifications they are wedged in position and maintain tension after the jacks are removed


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

Unbonded post-tensioned concrete

Unbonded post-tensioned concrete differs from bonded post-tensioning by providing each individual cable permanent freedom of movement relative to the concrete

Adv : The ability to individually adjust cables based on poor field conditions (For example: shifting a group of 4 cables around an opening by placing 2 to either side).


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

  • Rolls of post-tensioning

  • cables

2. Pulling anchors for

post-tensioning cables

3. Pulling anchors for

post-tensioning cables

6. Positioned post-t

ensioning cables

4. Pulling anchors for

post-tensioning cables

5. Post-tensioning cables stripped

for placement in pulling anchors


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

7. Post-tensioning cable ends

extending from freshly poured concrete

8. Post-tensioning cable ends

extending from concrete slab

10. Cable conduits

in formwork

9. Hydraulic jack for

tensioning cables


Prestressed concrete is a method for overcoming concrete s natural weakness in tension

Applications

Prestressed concrete is the predominating material for

Floors in high-rise buildings

Entire containment vessels of nuclear reactors

The advantages of prestressed concrete include crack control and lower construction costs; thinner slabs - especially important in high rise buildings in which floor thickness savings can translate into additional floors for the same

Increasing span lengths increases the usable unencumbered floor space in buildings

Diminishing the number of joints leads to lower maintenance costs over the design life of a building, since joints are the major focus of weakness in concrete buildings


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