76591575 Pre Stressed Concrete

7/30/2019 76591575 Pre Stressed Concrete

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INTRODUCTION

PRE-STRESSING

The process of induction of compressive

stresses in the structure before it is put to its

actual use is known as Pre-stressing.

Pre-stressed Concrete memberis amember of concrete in which internal

stresses are introduced in a planned manner,

so that the stresses resulting from the

superimposed loads are counteracted to adesired degree


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Pre-stressing is the intentional creation of permanent stress in a structure or

assembly, for improving its behaviour and strength under various service conditions.

In ordinary reinforced concrete, consisting of concrete and mild steel as basic

components, the compressive stresses are born by concrete while tensile stresses areborn entirely by steel. The concrete only acts as a binding material; it does not take

part in resisting the external forces.

In pre-stressed concrete, compression is induced prior to loading in the zones

where external loads would normally cause tensile stresses.

In the case of long beams, where large shear forces exist, the beam sizes have to be

large to limit the diagonal tensile stresses under certain limits. Pre-stress decrease

diagonal tensile stresses. This has led to adopt modified I-section and T-section in

which there is substantial reduction in web area.


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In order to get the maximum advantage of a pre-stressed concrete member, it is

necessary to use not only high strength concrete but also high tensile steel wires.

Concrete used for pre-stressed work should have cube strength of 35N/m m2 for

post-tensioned system and 45N/m m2 for pre-tensioned system.

In the design of a pre-stressed concrete member, the estimated loss of pre-stress

due to shrinkage of concrete and creep of concrete and steel is at the order of nearly

200N/m m2

Tendon

A high strength steelstrand or bar for pre-

stressing concrete

Abutment

A structure for anchoring

the reinforcing tendons in

the pre- tensioning of a

concrete member

Anchor

A mechanical device for locking of a stressed

tendon in position and delivering the pre-

stressing force to the concrete either

permanently in a post tensioned member or

temporarily during hardening of a pre-

tensioned concrete member

Jacking force

The tensile force exerted

temporarily by a jacking

the pre-stressing of a

concrete member


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Need of Pre-stressing

To offset the deficiency of tensile strength in concrete, steel reinforcement is provided

near the bottom of simple beams to carry the tensile stresses.

ADVANTAGES OF PRESTRESSED CONCRETE

1. Durability

As this technique eliminates weakness of concrete in tension, such members

remain free from cracks; hence can resist the effects of impact, shock, and reversal

of stresses more efficiently than R.C.C. structure.

They provide reliable long-term performance in extremely harsh conditions that

could destroy lesser materials.

They are resistant to deterioration from weather extremes, chemical attack,

fire,accidental damage and the determined efforts of vandals.

Winter construction can proceed with few weather delays as pre-cast components

are Prefabricated in heated plants.


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2. Adaptabil ity

Pre-cast pre-stressed concrete products can be designed and manufactured for any

application, ranging in size from short span bridges to some of the largest projects in

the world.

Permits pre-cast manufacturers to vastly expand the design variety possible using

pre-cast components.

the inherent plasticity of concrete permits to create pre-cast components in shapes

and sizes, which would be prohibitively expensive using other materials

3. F ire resistance

Pre-stressed concrete bridges are not easily damaged by fire. Have excellent fire

resistance, low maintenance costs, elegance, high corrosion resistance, etc.


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4. impacts local economy directly

Pre-stressed concrete is produced by local small business - employing local labour.

Most of its raw materials are also locally purchased and the health of the local pre-

stressed concrete industry directly impacts further on the local economy.

Due to smaller loads, due to smaller dimensions being used, there is a considerable

saving in cost of supporting members and foundations.

standard structural shapes such as hollow core, double tees, beams, columns and

panels can be mass-produced at low cost.

5. Fast and Easy Construction

Pre-cast concrete components lend themselves to fast construction schedules.

Pre-cast manufacturing can proceed while site preparation is underway.

Pre-cast units can be delivered to the jobsite and installed the moment they areneeded in any weather.

Fast construction means earlier completion and the resulting cost savings.

Saves the cost of shuttering and centring for large structures.


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6. Aesthetics

Pre-cast components can be delivered with a wide range of shapes and finishes

ranging from smooth dense structural units to any number of architectural

treatments.

Strikingly rich and varied surface textures and treatments can be achieved by

exposing colure sands, aggregates, cements and colourings agents using

sandblasting and chemical retarders.

custom form liners can be used to introduce reveals, patterns and otherarchitectural effects.

Stone, tile brick and other materials can be cast into pre-cast panels at the

factory,enabling designers to achieve the expensive look of masonry.


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DISADVANTAGES OF PRESTRESSED CONCRETE

Although pre-stressing has many advantages, there are still some drawbacks of

this process.

The unit cost of high strength materials being used is higher as mostly high

tensile steel is used.

extra initial cost is incurred due to use of pre-stressing equipment and its

installation.

extra labour and transportation cost for pre-stressing is also there.

pre-stressing is uneconomical for short spans and light loads.


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COMPARISON OF PRESTRESSED CONCRETE BEAMS WITH RCC

BEAMS

1. In RCC beams, the concrete in the compression side of the neutral axis alone is

effective and the concrete in the tension side is ineffective. But, in the pre-stressed beams, the entire section is effective.

2. Reinforced concrete beams are generally heavy. Pre-stressed concrete beams

are lighter.

3. RCC beams being heavy and massive are more suitable in situations where the

weight is more desired than strength. Pre stressed beams are very suitable for

heavy loads and long spans.

4. In RCC beams, there is no way of testing the steel and the concrete. In pre-

stressed concrete beams, testing can be done while pre stressing.

5. RCC construction does not involve many auxiliary units. But pre-stressedbeams require many auxiliary units.


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Assumptions in design of pre-stressed concrete members

Pre-stressed concrete members are analysed and designed on the basis of the

following assumptions given below: A transverse plane section of the member will remain a plane after bending

also.

Within the limits of the deformation taking, Hooks law is applicable to

concrete and steel components.

The stress in the reinforcement does not change along the length of the

reinforcement. Stress changes take place for the concrete component only.

Variation of stress in the reinforcement due to changes in the external loading is

ignorable.


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Principles of pre-stressing: -

large pre-stressing force are applied to the member by the tendons, high

bearing stresses are developed at the ends by the anchoring devices. The

anchorages are generally designed to be meant for use only for high strengthconcrete work.

Busting stresses liable to at the ends of the beam cannot be satisfactorily

resisted by low strength concrete work.

When stress transfer to concrete has to take place by bond action, the concreteshould have a high strength concrete.

Shrinkage cracks will be very little when high strength concrete is used.

Due to the high modules of elasticity of high strength concrete, the elastic and

creep strain are very small resulting in smaller loss of pre-stress in all steel

reinforcement.


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CLASSIFICATION OF PRE-STRESS CONCRETE

There are many ways of classifying pre-stress concrete members based of the

member of design, construction and application of pre-stress, some of them are

as follows:-

1. External or internal pre-stressing

2. Linear or circular pre-stressing

3. Pre-tensioning and post tensioning

Pre-tensioning system

(fully bonded constructions)

Post

tensioning system(end anchored constructions)

4. Full pre-stressing or partial pre-stressing
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Disadvantages

Prestress transferred to the member is likely to be lost due to any possible

outward displacements of the abutments.

Shrinkage and creep of concrete are

likely to affect the initially applied prestress.Even slight vertical deformations of the supports

will disturb the stresses seriously.

A. EXTERNAL AND INTERNLLY PRESTRESSED MEMBERS

In External Prestressing, the member

is prestressed by external reaction offered

by rigid abutments. In this, the necessary prestressing force can be

applied by compressing the member by jacking against abutments.

A sliding surface may be provided underneath the beam.

After the prestressing is over, the space between the end of the beam and the

abutment may be packed with concrete and the jack recovered.

In Internal Prestressing tendon is provided from which the prestress

can be applied


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B. LINEAR OR CIRCULAR PRESTRESSING.

Linear prestressing is a term applied to prestressing straight members like

beams and slabs.

The term circular prestressing is applied to prestressing circular structures

like cylindrical tanks, silos and pipes. In this case, the tendons are provided in the

form of rings


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One end of the reinforcement (i.e. tendon) is

secured to an abutment while the other end of

the reinforcement is pulled by using a jack and

this end is then fixed to another abutment.

The reinforcement which tends to resume i ts

or igin al lengthwill compress the concrete

surrounding it by bond action. Theprestressis thus transmitted to concrete entirely by the

action of bond between the reinforcement and

the surrounding concrete.

Pre-tensioned members-In these, the tendons

are tensioned even before casting the concrete.

C. PRE-TENSIONING AND POST TENSIONING

The concrete is now poured. After the concrete has cured and hardened, the

ends of the reinforcement are released from the abutments.


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When the concrete has hardened and

developed its strength, the tendon is passed

through the duct.

One end is provided with an anchor and is

fixed to one end of the member.

Now, the other end of the tendon is pulled by

a jack which is butting against the end of the

member.

The beam is first cast leaving ducts for placing the tendons.

The ducts are made in a number of ways - by leaving corrugated steel tube

in the concrete, by providing steel spirals, sheet metal tubing, rubber have orany otherduct forming unitin the form work.

The jack simultaneously pulls the tendon and compresses the concrete.

After the tendon is subjected to the desired stress, the end of the tendon is

also properly anchored to the concrete.

To avoid crushing of concrete due to excessive bearing stress, a distribution

plate is provided at each end.

Post-tensioned member- It is one in which the reinforcement istensioned afterthe concrete has fully hardened.


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SYSTEMS OF PRESTRESSING

A system of prestressing means the actual process adopted in making a

prestressed beam. A system of prestressing involves :

process of tensioning the tendons

securing them firmly to the concrete

A. Pre-tensioning system

Wires are stretched between two bulkheads at large distance apart.

The concrete is now poured so that a number of beams can be produced in one

line, by providing suitable shuttering between them.

HOYER SYSTEM

The Hoyer system is usually adopted for the production of pre-tensioned members

on a large scale like precast beams.

After the concrete has hardened, the wires are released from

the bulkheads and between the different units in one line ofbeams.

The prestress is transferred to the concrete through bond

between the tendons and the concrete.

Pre-tensioning system is found uneconomical for large spans.

In order to grip the pre-tensioned wires properly to the bulkhead the devices areshown


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SYSTEMS OF POST- TENSIONING

1. THE FREYSSlNET SYSTEM

High tension steel wires 5 mm to 8 mm diameter about

12 in number are arranged to form a group into a cablewith a spiral spring inside.

The spiral spring provides

proper clearance between the wires

and thus provides a channel which

can be cement grouted.

It further assists to transfer thereaction to concrete.

The anchorage consists of a good quality concrete cylinder and is provided with

corrugations on the outside. It has a central conical hole and is provided with heavyhoop reinforcement.

The conical plugs are pushed into the conical holes after cables are tightened. The

central hole passing axially through the plug permits cement grout to be injected

through it.

In this way the space between the wires will be filled with the grout. This provides

additional restraint against the slipping of the tendons.

The whole thing is enclosed in thin metal

steel.


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Advantage of the system

(i) Securing the wires is not expensive.

(ii) The desired stretching force is obtained quickly.

(iii) The plugs may be left in the concrete and they do not project beyond the endsof the member.

Disadvantage of the system

(i)All the wires of a cable are stretched together. Hence the stresses in the wiresmay not be exactly the same.

(ii) The greatest stretching force applied to a cable is from 250 KNto 500 kN. This

may not be sufficient.

(iii) The jacks used are heavy and expensive.


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The geometric pattern of the wires is maintained throughout the length of the

cable by providing grills or spacers at regular intervals. The grills do not offer

any appreciable frictional resistance to the wires which can be moved relative to

each other during the tensioning process.

The wires are anchored by wedging, two at a time into sandwich plates (25

mm thick and are provided with two wedge-shaped grooves on its two faces).

The wires are taken two in each groove and tightened by jacking two wires at a

time.

Then a steel wedge is driven between the tightened wires to anchor them

against the plate.

Each plate can anchor eight wires. The various sandwich plates forming a unit

are arranged one above the other against a distribution plate.

2. THE MAGNEL BLATON SYSTEM

In this system a cable of rectangular

section is provided, which contains layers of

wires 5 mm to 8mm diameter.

The wires are arranged with four wires

per layer. The wires in the same layer and the

wires in adjacent layers are separated with a

clearance of4mm.


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3. GIFFORD UDALL SYSTEM

This method offers the following three methods

of prestressing:

First method

This is earliest of the three methods of this system.

In this method the wires are stressed and anchored one by one in a separate

cylinder using small wedging grips called udal l gr ips.

Each grip consists of two-half cones.

The bearing plate bears against a thrust ring which is cast into the concrete.The duct end is encircled by a helix.

Anchorages are supplied to suit cables of 2, 4, 6 and 12 wires.

Second method

In this method, the wires are anchored by wedges which

fit directly into tapered recesses made in the bearingplate.

The bearing plate bears against a tube unit containing the tube unit and the helix.

This tube unit is cast into the concrete.

Anchorages are supplied for cables of 8 to 12 wires.

This arrangement is compact and minimizes the congestion of the steel wires inanchor block.


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4. P.S.C. MONOWIRE SYSTEM

MONOWIRE SYSTEM

In this system also the wires are tensioned

individually.

The anchorage consists of a single piece

collet sleeve wedging in a concial hole.

A steel truncated guide leads each wire

from the cable to the anchorage point along a

gentle curvature.

In addition to the guide a central block is also

provided to anchor the central wires.

5. ELECTRICAL PRESTRESSING

This is a method of post tensioning without the use of jacks introduced by

Bittner and Carlson,

Steel bars are provided with a coating of su]phur, before they are embedded in

concrete.

After the hardening of concrete electric current of low voltage and high

amperage is used to heat the bars to a temperature of 1700 C.

As the bars expand longitudinally, the nuts on the projecting ends are tightened

against heavy washers.

As the temperature falls, the prestress is developed in the bars and the bond isagain restored by the resolidification of the sulphur coating.


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Post-tensioning system

In order to ensure the correct prestress in the reinforcement, it is preferable to

measure the load applied by the jack as well as the consequent extension of the

reinforcement.

Extension measurements give an idea as to how much of the steel is being

properly stretched.

For instance the sides of the ducts may obstruct the stretching of the

reinforcement particularly at the end remote from the jack and this part of the

reinforcement may not receive the full tension. This defect is liable to occur

when curved cables are provided. On the other hand; it may be possible that the extension might have taken place

due to a certain part of the tendon being overstressed. For this reason, it is

necessary to measure the prestressing force applied.

Excessive bearing stresses will be produced at the ends of the members due to

the anchoring devices which bear against the concrete. In this part of the member itwill be necessary to provide additional reinforcement to prevent local splitting and

failure by shear.


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SUITABILITY OF THE SYSTEM

Pre-tensioning and post tensioning are the only practically adopted

methods of making prestressed concrete members.

In pre-tensioning, the compressive force in concrete is due to the bond between

concrete and the steel wires, which are kept stretched between buttresses.

This method is economically adopted in mass production in factories which

make concrete products of limited size.

This is so because, handling as well a transporting large products are highly

expensive and may be practically impossible, if thee members are too large.The length of a prestressed concrete product that can be economically made by

this method may not exceed 20 m. Even this length involves considerable

difficulty in transport.00

In post tensioning, the prestressing wires are stretched after the hardening of

concrete. This can be done by many ways like the following:

These methods can be adopted in sites or on the ground, and later hoisted int

position. For instance, if timber is costly or scarce it may be economical to make

the member on the ground in steel moulds.


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MATERIALS FOR PRE-STRESSED CONCRETE:

1- High-Strength Concrete:

High strength concrete mix:Pre-stressed concrete requiresconcrete which has a highcompressive strength, withcomparatively higher tensile strength.Low shrinkage, minimum creep

characteristics and a high value ofYoungs modulus are generallydeemed necessary for concrete usedfor concrete used for pre-stressedmembers.

A minimum cement content of 300 to 360 kg/m3 is prescribedmainly to cater to the durability requirements. In high-strengthconcrete mixes, the water content should be as low as possiblewith due regard to adequate workability.To safeguard against excessive shrinkage, the code prescribesthat the cement content in the mix should preferably not

exceed 530kg/m3.

A t f k t h i hi h d li f l ti it d l


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Aggregate of rock types having high moduli of elasticity and lowvalues of differed strain are more effective in restraining thecontraction of the cement paste and their use reduces theshrinkage of concrete. The commonly used aggregates, inincreasing order of effectiveness in restraining shrinkage, are

sand-stone, basalt, granite, quartz and limestone.

The values of total residual shrinkage strain recommended in theI.S. code for the purpose of design are 3.0X10-4 for pre-tensionedmembers and(2.0X10-4)/log(t+2) for post-tensioned members,where t is the age in days of the concrete at transfer.

The main advantage of light weight concrete is that it reduces the

selfweight of the structure, thus minimizing the amount of concrete

and steel required for carrying the load.

The light weight criterion becomes important especially in long span

structures where dead load forms the major portion of the total design

load on the structure, or when the self-weight of the member is a

factor to be considered in the transportation and erection, as in pre-

cast concrete construction.

Light-weight Aggregate Pre-stressed Concrete:


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The light-weight aggregates, generally used for pre-stressed concrete are foamed slag, lytag and aglite.

The modulus of elasticity of light-weight concrete isabout 50 to 55 percent of the modulus of elasticity ofnormal- weight concrete and hence the loss of pre-stress due to elastic deformation is higher anddeflections of flexural members are comparativelyhigher due to the lower values of modulus of elasticity.

The unit weight of light-weight concrete variesconsiderably between 1450 and 1750 kg/m3.

The shrinkage and creep of light-weight concrete iscomparable, with marginal variations, to that of sandand gravel concrete.


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2- High -Tens ile Steel:

For pre-stressed concrete members, the

high tensile steel used generally consists of

wires, bars, or strands.

The higher tensile strength is generally

achieved by marginally increasing the

carbon content in steel in comparison with

mild steel.

High tensile steel usually contains 0.60 to

0.85 percent carbons, 0.70 to 1.00 percent

manganese, and 0.05 percent of sulphur and

phosphorus with traces of silicon.

The high-carbon steel ingots are hot-rolled into rods and cold-drawn through a series of dies to reduce the diameter and increasethe tensile strength.

The process of cold-drawing through dies decreases the durabilityof the wires. The cold-drawn wires are subsequently tempered toimprove their properties. Tempering or ageing or stress relievingby heat treatment of the wires at 150-420oC enhances the tensilestrength. The cold drawn stress relieved wires are generallyavailable in nominal sizes of 2.5,3,4,5,7 and 8mm diameter and

they should confirm to the Indian standard code IS: 1785-1983.


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The hard drawn steel wires which are

indented or crimped are preferred for

pre-tensioned elements because of their

superior bond characteristics. The small

diameter wires of 2 to 5 mm are mostlyused in the form of strands comprising

two, three or seven wires.

The high-tensile steel bars commonly

employed in pre-stressing are

manufactured in nominal sizes of10,12,16,20,22,25,28 and 32mm diameter

and are covered in IS:2090-1983.

The ultimate tensile strength of a plain-

drawn steel wire varies with its diameter.

The tensile strength decreases with

increases in the diameter of the wires.

And referred in the relevant Indian

standard codes.


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LOSS OF PRE-STRESS

A reduction in initial pre-stress resulting from the combined effect of

creep, shrinkage or elastic shortening of the concrete, relaxation of the

reinforcing steel, frictional losses resulting from the curvature of thedraped tendons and slippage at the anchorage.

The steel wires of a pre-stressed concrete member do not retain all

the preliminary pre-stress .

The initial pre-stress in concrete undergoes a gradual reduction withtime from the stage of transfer due to various causes.

A loss of pre-stress will affect the stress distribution on the section of

the member.


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The loss of pre-stressed takes place due to many causes. In general these can be

classified as:

Loss of pre-stress during the tensioning process

Loss of pre-stress at the anchoring stage.

Losses occurring subsequently

PRE-TENSIONING POST-TENSIONING

Elastic deformation of concrete

Relaxation of stress in steel

Shrinkage of concreteCreep of concrete

1.No loss due to elastic deformation if allthe wires are simultaneously tensioned. If

the wires are successively tensioned there

will be loss of pre-stress due to elastic

deformation of concrete

2.Relaxation of stress in steel

3.Shrinkage of concrete4.Creep of concrete

5.Friction

6.Anchorage slip


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In addition there may be losses of pre-stress due to sudden changes in temperature,

especially in steam curing of pre- tensioned units.

The rise in temperature causes a partial transfer of pre-stress (due to elongation of the

tendons b/w adjacent units in the long line process) which may cause a large amount of

creep if the concrete is not properly cured.

LOSS OF PRE-STRESS DURING THE TENSIONI NG PROCESS DUE TO

FRICTION

Friction in the jacking and anchoring system and on the walls of the duct where the

wires fan out at the anchorage with the result, the actual stress in the tendons is less thanwhat is indicated by the pressure gauge.

The losses due to friction in the jack and at the anchorage are different for different

system of pre-stressing.

This loss due to friction may be classified into:Loss Due To Length Effect

The extent of friction met with in a straight tendon due to slight imperfection of the duct

(the straight tendon).

Hence the cable will touch the duct or concrete, wobbing effect, or wave effect


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Loss due to curvature effect

In the case of curved ducts, the loss of pre-stress depends upon the radius

of curvature of the duct and the coefficient of friction between the duct surface and the

tendons.

LOSS OF PRESTRESS AT THE ANCHORING STAGE

This loss is dueto the fact that the anchorage fixtures themselves are subjected to a

stretch.

It is also possible that the friction wedges holding the wires the wires may slip a little The necessary additional elongation may be provided for at the time of tensioning to

compensate for this loss.

LOSS OF PRESTRESS OCCURIING SUBSEQUENTLY

The loss which occur subsequently to pre-stress are:

Loss Of Stress Due To Shrinkage Of Concrete:

Contraction of concrete due to chemical changes and drying. This depends only on the

interval of time and the moisture conditions, but is independent of the stresses in the

members due to loads


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By minimizing the water cement ration and proportion of cement, the shrinkage can

be reduced.

Loss Of Stress Due To Creep Of Concrete

Creep of concrete means the deformation of concrete, which depends upon theinterval of time to which the member is loaded

This additional deformation of the stressed member is remaining in a stressed state is

called CREEP.

Loss Of Stress Due To Elastic Shortening Of Concrete(a) Pre-tensioned member

Due to the pre-stress transfer to the concrete, the concrete will shorten. This results

in a corresponding shortening of steel

(b) Post tensioned member

Suppose only a single tendon has been provided in a member, the concrete gets

shortened as the tendon is jacked against it.

Hence, after tightening, no more shortening of concrete can take place


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Loss Of Stress Due To Creep Of Steel(Stress Relaxation)

Total loss of pre-stress depends on many factors such as properties of concrete and

steel, moisture and curing condition, the magnitude and system of pre-stress

The first three types of losses take place due to reduction in the length ofconcrete resulting in reduction in reduction of the initial extension of the steel.

The loss of stress due to elastic shortening of concrete is maximum in pre-

tensioned members.

In the case of post

tensioned members those losses occur only when a numberof cables are progressively stressed one after another.


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APPLICATIONS OF THE PRE-STRESSED CONCRETE:Concrete is an all-round construction

material. Almost every building contains

some concrete, but its questionable

application in certain buildings-for examplein its use in the style of brutalism - has

brought it into discredit. Its dull grey colour

has contributed to the fact that the word

concrete has become a synonym for ugly. In

the field of bridges, concrete deserves a morefavourable judgement.

Not all concrete bridges have turned out

to be beauties, but pleasing bridges can be

built with concrete if one knows the art.

Concrete is poured into forms as a stiff butworkable mix, and it can be given any

shape; this is an advantage and a danger.

The construction of good durable concrete

requires special know-how - which the

bridge engineer is assumed to have.

MEGA FLOOR,the Prestressed

slab

Slab:Hollow core slab,Preslab

or predalle ,prestressed ribs andblocks , lintels.

Beam: Prestressed rectangular

beam and I-beam for bridges

Other prestressed components:

Lintels , Wineyard stud.
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Pre-stressed concrete - if correctly designed - also has high fatigue strength under

the heaviest traffic loads.

Pre-stressed concrete bridges soon became much cheaper than steel bridges, and

they need almost no maintenance - again assuming that they are well designed and

constructed and not exposed to de-icing salt.

In bridge building, concrete beams and arches predominate. Theshaping of concrete is usually governed by the wish to use formwork,which is simple to make. Plain surfaces, parallel edges and constant

thickness are preferred. This gives a stiff appearance to concretebridges, and avoiding this is one task of good aesthetic design

All types of structures can be built with reinforced and pre-stressedconcrete: columns, piers, walls, slabs, beams, arches, frames, evensuspended structures and of course shells and folded plates.

Tanks

Foundation panels

Poles

Modular block retaining wall system


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Wall panels

Concrete units

Slabs

Roofing and flooring

Lintel and sunshade

Beams

Columns girders

TANKS

STRAND Wrapped circular pre-stressed concrete

tanks are long life liquid storage structure with virtually

no maintenance.

Concrete construction makes for a substantial, sturdytank structure that easily contain the internal liquid

pressure while comfortably resisting external forces

such as earthquake, wind.

U


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Uses

These tanks are used in portable water treatment and distribution system,

wastewater collection and treatment system and storm water management.

They are also used in a variety of commercial applications including thermal energystorage, LNG containments, large industrial process tanks and large bulk storage

tanks.

Water

Pre-stressed concrete is the most efficient material for water tanks and coupled with

the circular shape, eliminates all stress conditions.

By placing the steel of the pre-stressed strands in tension and the concrete in

compression, both materials are in an ideal states and the loads are uniformly

distributed around the tank circumference.

PROPERTIES

Low maintenance can be enjoyed throughout

the life as these are built with concrete,

durable material that never corrodes and does

not require coatings when in contact with

water or the environment.


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Pre-stressing counteracts the differential temperature and dryness loads that a

tank core wall experience. The tank walls are wet on the inside and dry on outside

and the temperature varies between the two sides. If not properly accounted for,

these moisture and temperature differential will cause a tank wall to bend and

crack. Counteract these force in both the vertical and horizontal direction anddiminish subsequently the cracking and leaking

Tanks are very ductile, enabling to withstand seismic forces and varying water

backfill.

Tanks utilize material efficientlysteel in tension, concrete in compression

Pre-cast tanks can store or treat anything from potable water to hazardous waste

to solid storage bins.

Storage capacities can range from 0.4 to 120 mega liters

Diameters of the tank can vary upto 90 m

METHOD


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METHOD

Pre-cast concrete wall elements are usually pre tensioned vertically in the

plant and post tensioned horizontally through ducts cast in the panels.

Vertical pre stressing diminishes vertical bending in the wall and subsequentleakage

Circumferential pre-stressing counteracts bursting loads from interior liquid.

Joints closures are usually poured concrete on site. This method of sealing

the joints allow the tank to [perform (after posttensioning) as a monolithic

structure to resist hydraulic, temperature and seismic forces.

SHAPE OF THE TANKS

FOUNDATION PANELS


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FOUNDATION PANELS

PRECAST CONCRETE foundation panels consist of

steel reinforced concrete studs, reinforced tops and

bottom beams and concrete facing.

Insulation can be placed between the studs.

A typical panellised foundation can be erected in four to

five hours, according to a manufacturer, with no on site

concrete work (the panels sit on gravel bed in lieu of

footings.)

DETAILS

WALL PANELS


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WALL PANELS

Fast Track Easy Installation

Low Cost Walling

Durable Low Maintenance Walling

All Weather Construction

No Trades Foundation Free Walling

High Impact Resistance Cladding

Protection

Added Security and Fire Stop

Properties

Steel Frame Compatible Walling

System

Fast Simple and Robust Angle Bracket

Connection

Tongue and Groove Joints

Variable Height Walling

Simple Top Lifter Installation

Any Length

Ideally suited for many Building

Application such as Industrial, Light

Industrial & Commercial, Heavy Duty

Warehousing, Bulk Storage and Waste

Transfer StationsPre-stressed Concrete Panel

Division are manufacturers and

suppliers of pre-stressed concrete

panels for use in both agricultural and

construction industries.

These panels are used in avariety of applications including fast

track wall construction, retaining

walls, bulk storage bunkers, grain

stores and silage clamps.

Manufactured in lengths of up to

7000mm, the pre-stressed panels areoffered in a selection of thickness to

suit various applications and a range

of widths. Their simple clamp bracket

connection and tongue/grooved profile

make for a fast and efficient

installation system.

POLES


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POLES

Low maintenance, competitive price and aesthetic appearance of the pre-cast concrete

poles make them superior to steel or wood for use in utility, communication area lighting

application

The use of concrete poles preserve our forest requires no chemical treatment andutilizes environmentally safe materials in he production and placement.

Some other benefits are corrosion resistance, long service life

Because of mineral vibration and deflection, pre-cast concrete poles offer greater

service life to ballast for light and this in turn means less down time and less costly

equipment repair.

Pre-cast concrete poles can save erection time and money by eliminating the need for

anchor based structure, which may take days or weeks to install.

PRECAST STAIRS AND LANDINGS

Straight FlightsIntegral Landings

(quarter/half landings)Separate Landings


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MODULAR BLOCK RETAINI NG WALL SYSTEM

Modular block or segmental, retaining walls employ

interlocking concrete units that tie back into the earth to

efficiently resist loads.These pre- engineered modular systems are an

attractive, economical and durable an alternatives to

atone or poured concrete retaining walls.

The inherent design flexibility can accommodate a

wide variety of site constraint, project sizes and

aesthetic preferences.

BENEFITS

Controlled manufacturing conditions ensures a durable, damage resistant product.

These systems allow for some flexibility, such as curved walls .

Construction is generally faster than poured in place concrete or stonewalls

Site conditions have a major impact on cost

APPLICATIONS ( l )


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APPLICATIONS (some examples):

The following fig. Shows the typical pre-stressed concrete flat slab floor construction

using the lift slab technique

Pre-stressed concrete twin box

girder bridge construction usingthe segmentally cast cantilever

method

Chaco-corrientes Bridge,

Argentina, The longest pre-castpre-stressed concrete

Cable stayed box Girder Bridge

In South America

Pre-stressed concrete

folded plate roof

13-storey apartment building with pre-cast

Post tensioned lift slab construction, 203mm

Thick lightweight concrete slab of 8.6m spans,

SAN FRANSICO

Documents

76591575 Pre Stressed Concrete