Systems of Prestressing

8/20/2019 Systems of Prestressing

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SYSTEMS OF

PRESTRESSING


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Prestressing systems have developed over the years

Various companies have patented their products

Detailed information of the systems is given in the pcatalogues and brochures published by companies.

There are general guidelines of prestressing in SectiIS:1! " 1#$%

The prestressing systems and devices are described

types of prestressing' Pre(tensioning

Post(tensioning


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P)*T*+SI,+I+- SST*/

Tendons are pulled between two end abutments prior to the cas

The abutments are fixed at the ends of a prestressing bed.Once the concrete attains the desired strength for prestressing, t

cut loose from the abutments.

The prestress is transferred to the concrete from the tendons, du

between them.

During the transfer of prestress, the member undergoes elastic s

If the tendons are located eccentrically, the member is likely to


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D*VI*S ,) P)*T*+SI,+I+-

Prestressing bed

*nd abutments

Shuttering 3 mould

4ac5 0nchoring device


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9oyer system for mass production


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The end abutments have to be suciently sti; and hafoundations.

The necessity of sti; and strong foundation can be by

simpler and cheaper option. It is possible to avoid transmitting the heavy loads to

by adopting self(e


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The frame that is generally adopted in a pre(tensionin

is called a stress bench. The concrete mould is placed &ithin the frame and the

are stretched and anchored on the booms of the frame


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40AS

The @ac5s are used to apply tension to the tendons.

9ydraulic @ac5s are commonly used.

These @ac5s &or5 on oil pressure generated by a pump The principle behind the design of @ac5s is Pascal>s la&

The load applied by a @ac5 is measured by the pressurefrom a gauge attached to the oil inBo& or by a separat


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0+9,)I+- D*VI*S 0nchoring devices are often made on the &edge and f

principle.

In pre(tensioned members' the tendons are to be held during the casting and hardening of concrete.

9ere simple and cheap


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SST*/S


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9ere the ducts for the tendons are placed along &ith

reinforcement before the casting of concrete. The tendons are placed in the ducts after the casting

The duct prevents contact bet&een concrete and theduring the tensioning operation.

Tendons are pulled &ith the reaction acting against t

concrete. If the ducts are ?lled &ith grout' then it is 5no&n as

tensioning.


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The grout is a neat cement paste or a sand(cement containing suitable admiture.

In unbonded post(tensioning ' the ducts are never gr

the tendon is held in tension solely by the end ancho The follo&ing s5etch sho&s a schematic representat

grouted post(tensioned member.

or a simply supported member' the duct has a saggbet&een the ends.

or a continuous member' the duct sags in the span over the support.


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asting of concrete.

Placement of the tendons.

Placement of the anchorage bloc5 and @ac5.

0pplying tension to the tendons.

Seating of the &edges. utting of the tendons.


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0STI+- 6*D ' /,78D 0+D D7TS


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C*D-* 0TI,+

The anchoring device based on &edge action consist

anchorage bloc5 and &edges. The strands are held by frictional grip of the &edges

anchorage bloc5.

0n eample of system based on the &edge(action are-i;ord(7dall' 0nderson and /agnel(6laton anchorage

The follo&ing ?gures sho& some patented anchoring


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8,,PI+- , T9* CI)*S

The 6aur(8eonhardt system' 8eoba system and also

D&idag single(bar anchorage system' &or5 on this p The &ires are looped around the concrete.

The &ires are looped to ma5e a bulb.

The follo&ing photo sho&s the anchorage by looping&ires in a post(tensioned slab.


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S*G7*+* , 0+9,)I+-


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40AS

The &or5ing of a @ac5 and measuring the load &ere disin the previous portion about the Pre(tensioning Syste

Devices .

The follo&ing ?gure sho&s an etruded s5etch of theanchoring devices


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,7P8*)S

The couplers are used to connect strands or bars.

They are located at the @unction of the members' for eat or near columns in post(tensioned slabs' on piers inposttensioned bridge dec5s.

The couplers are tested to transmit the full capacity ostrands or bars. 0 fe& types of couplers are sho&n

-),7TI+-


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-),7TI+-

-routing can be de?ned as the ?lling of duct' &ith a mprovides an anti(corrosive al5aline environment to theprestressing steel and also a strong bond bet&een the

and the surrounding grout. The ma@or part of grout comprises of &ater and cemen

&ater(to(cement ratio of about %.H' together &ith somereducing admitures' epansion agent and poolans.

The follo&ing ?gure sho&s a grouting e


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SST*/S


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Systems of Prestressing

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