PRESTRESSED CONCRETE

Prestressed Concrete

Definition: 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.

History BackgroundO THE BICYCLE WHEEL

Bicycle wheel as we know it today - each is associated with an application of prestressing to a structural system.

Pre-tensioned concreteBonded post-tensioned concreteUnbonded post-tensioned concrete

Methods of Prestressing:

In pre-tensioning the reinforcement, in the form of tendons or cables, is stretched across the concrete formwork before the concrete is placed.

Pre-tensioned concrete

Bonded post-tensioned concrete is the descriptive term for a method of applying reinforced after pouring concrete and the curing process

Bonded post-tensioned concrete

1) Tendons are less likely to de-stress in accidents2) Tendons can be easily 'weaved' allowing more

efficient designs3) Higher ultimate strength due to bond generated

between the strand and concrete

Advantages of bonded 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.

Unbonded post-tensioned concrete

1) Ability to de-stress the tendons2) Economical 3) Replaceable4) Simple stressing equipment

Advantages of Unbonded post-tensioned concrete

1) W I R E S 2) S T R A N D S3) T E N D O N4) C A B L E 5) B A R S

Forms of Prestressing Steel

Prestressing wire is a single unit made of steel.

Wires

Two, three or seven wires are wound to form a prestressing strand.

Strands

A group of strands or wires are wound to form a prestressing tendon.

Tendon

A group of tendons form a prestressing cable.

Cable

A tendon can be made up of a single steel bar. The diameter of a bar is much larger than that of a wire.

Bars

Common shapes of prestressing tendons.

Among these 7-wire strand is most popular

Difference between RC,PC and PPC

Applications of prestressed concrete:1) Bridges2) Slabs in buildings3) Water Tank4) Concrete Pile5) Thin Shell Structures6) Offshore Platform7) Nuclear Power Plant

Advantages of Prestressing

Prestressing minimizes the effect of cracks in concrete elements by holding the concrete in compression.

Prestressing allows reduced beam depths to be achieved for equivalent design strengths.

If the member is subject to overload, cracks, which may develop, will close up on removal of the overload.

Lighter elements permit the use of longer spanning members with a high strength to weight characteristic.

Prestressed concrete can provide significant cost advantages over structural steel sections or ordinary reinforced concrete.

Limitations of Prestressing

Prestressing needs skilled technology. Hence, it is not as common as reinforced concrete.

There is need for quality control and inspection.

The use of high strength materials is costly.

May Allah shower His blessings on us!

Aameen!