PRESTRESS CONCRETE

Submitted to submitted by: Prof A.B.GUPTA BATTI LAL MEENA

2011UCE1094

What is prestressed concrete ?

Definition:

“Pre-stressed concrete is a form of reinforced

concrete that builds in compressive stresses during

construction to oppose those found when in use.”

In other words it is a combination of steel and concrete

that takes advantages of the strengths of each material.

Types of Internal Prestressed Concrete

Main three types of prestressed concrete:-

Pre-Tension Concrete:- : pre-stressing steel is tension stressed earlier to the placement of the concrete and unloaded after concrete has harden

Bonded post-tensioned concrete: unstressed pre-stressing steel is placed with in the concrete and then tension stressed after concrete has harden to required strength

Un-bonded post-tensioned concrete: differs from bonded post-tensioning by providing the pre-stressing steel permanent freedom of movement relative to the concrete

http://en.wikipedia.org/wiki/Prestressed_concrete#Bonded_post-tensioned_concrete

Pre-tensioned Concrete:-

Pre-tensioned concrete is when the steel reinforcement is

stressed prior to concrete being placed around the steel

This method produces a good bond between the tendon

and concrete which both protects the tendon from

corrosion and allows for direct transfer of tension.

Advantages of Pretension:-

Pretension is the easiest controlled of the bonded

stresings with the least chance of error in the bonding

process.

Allow to carry a greater load or soan greater distance

then ordinary reinforce concrete .

It permits steel to be used at stresses serveral times large

then permitted for reinforcing bars

Post-tensioned Concrete:-

Post tensioning is a method of reinforcing concrete or

other materials with strength steel stands or bars typically

referred to as tendons .

Post tensioning application include office and apartment

building parking structures slabs –on-ground bridge sports

stadiums rocks and soil anchors and water tanks

Type of post tensioned concrete:-

They are classified two types tensioned

concrete :–

1 . bonded post tensioned concrete .

2 . Unbonded post tensioned concrete .

Bonded post tensioned concrete :-

Concrete is the descriptive term for a method of

applying “ compression” after the pouring

concrete process .

The concrete is cast around a plastic steel or

aluminium curved duct to follow the area where

othereise tension would occur in the element

Un bonded post tensioned concrete :-

Un bonded post tensioned concrete differs from

bounded post tension by providing each individual

cable permanent freedom of movement relative

to the concrete .

To achieve this individual tension (generally

lithium based )and covered by a plastic sheathing

formed in an extrusion process .

Advantages of post-tensioned concrete:-

Tendons can be easily “woven” allowing a move efficient

design approach

Higher ultimate strength due to bond generated between

strand and concrete

Large reduction in traditional reinforcement requirement

as tendons can not distress in accidents

Post tension cable :-

APPLICATIONS:

Post-tensioning allows longer clear

spans, thinner slabs, fewer beams and

more slender, dramatic elements.

Thinner slabs mean less concrete is

required. It means a lower overall

building height for the same floor-to-floor

height.

Post-tensioning can thus allow a

significant reduction in building weight

versus a conventional concrete building

with the same number of floors

reducing the foundation load and can be

a major advantage in seismic areas.

A lower building height can also

translate to considerable savings in

mechanical systems and façade costs.

This innovative form is result of

post tensioning.

Conti…

Another advantage of post-tensioning is that beams and slabs can be continuous,

i.e. a single beam can run continuously from one end of the building to the other.

Reduces occurrence of cracks .

Freezing & thawing durability is higher than non prestressed concrete.

Bridge decks

Post-tensioning is the system of choice for parking

structures ,since it allows a high degree of flexibility in the

column layout, span lengths and ramp configurations.

In areas where there are expansive clays or soils with

low bearing capacity, post-tensioned slabs-on-ground

and mat foundations reduce problems with cracking and

differential settlement.

Post-tensioning allows bridges to be built to very

demanding geometry requirements, including complex

curves, and significant grade changes.

Post-tensioning also allows extremely long span bridges

to be

constructed without the use of temporary intermediate

supports. This minimizes the impact on the environment

and avoids disruption to water or road traffic below.

In stadiums, post-tensioning allows long clear spans and

very

creative architecture. \

Conti..

Conti…

Post-tensioning can also be used to produce virtually crack-free concrete for

water-tanks.

The high tensile strength & precision of placement gives maximum efficiency in

size & weight of structural members.

Applications of various prestressed techniques enable quick assembly of

standard units such as bridge members, building frames, bridge decks

providing cost-time savings.

References:

http://en.wikipedia.org/wiki/Prestressed_concrete

http://www.aboutcivil.org/concrete-technology

www.cement.org/cement-concrete-basics/concrete...

How is Unbonded Post Tensioning Made?

Jump up^ Detensioning Unbonded Post-Tension Tendons

Jump up^ Barrier Cable

Jump up^ Cement & Concrete Basics: Prestressed Concrete | Portland

Cement Association (PCA)

www.grtinc.com/

www.theconcreteinstitute.org.za/wp...

Thank you