whatisprestressedconcrete-140722125453-phpapp01

7/25/2019 whatisprestressedconcrete-140722125453-phpapp01

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a s res resseConcrete?

It is a method of applying pre-compression to control the

stresses resulting due to externalloads below the neutral axis of thebeam.

Pre-compression resulting eitherno tension or compression.

J.D. COLLEGE OF ENGINEERING, NAGPR


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Basic Concept

Prestressed concrete is basically concrete inwhich internal stresses of a suitablemagnitude and distribution are introduced so

that the stresses resulting from the externalloads are counteracted to a desired degree.

Pre-stress is introduced by stretching steel

wire and anchoring them against concrete.



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History

!ugene "reyssinet#"rance$

%sed high tensile steel wires&with ultimate strength ashigh as '()* +Pa and yieldstress o,er ') +Pa. In'/0/& he de,eloped conical

wedges for end anchoragesfor post-tensioning andde,eloped double-acting1ac2s. He is often referred toas the Father ofPrestressed concrete.1938 Hoyer, E., (Germany)

3e,eloped 4long line5 pre-tensioningmethod.

1940 Magne, G., (!eg"#m)3e,eloped an anchoring system forpost-tensioning& using 6at wedges.



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History

In India& the applications of prestressed concretedi,ersi7ed o,er the years. 8he 7rst prestressed concretebridge was built in '/9 under the :ssam ;ail


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Prestressed concrete was started to be used inbuilding frames& par2ing structures& stadiums& railwaysleepers& transmission line poles and other types ofstructures and elements.

+aterials for pre-stress concrete member

'. Cement& ). Concrete&

0. =teel.

> Cement

> @rdinary portland cement&

> Portland slag cement&

> ;apid hardening portland cement&

> High strength ordinary portland cement.


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> Concrete

Pre-stress concrete reAuires high strengthconcrete& which has high compressi,e strength

comparati,ely higher tensile strength than ordinaryconcrete.

8he concrete is a material should becompose of gra,els or crushed stones& sand& cement.

In pre-stress concrete minimum grade of

concrete +).>=teel

High tensile steel& tendons& strands.

In pre-stress concrete high tensile steel withtensile strength around )+Pa.

:ccording to I= '00-'/9 prestress concrete isdesign.


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8ypes of Pre-stressing

'. !xternal or internal pre-stressing.

It is based on the location of the pre-stressing

tendons with respect to concrete section.

). Pre-tensioning or post-tensioning.

It based on the seAuence of casting the concrete andapplying tension to the tendons.

0.


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Pre-tensioning : method of prestessingconcrete in which tendons are tens"oned$eforethe concrete is placed.

8he operation commonly a %&ste'process.

Post-tensioning : method of prestessingconcrete in which tendons are tens"onedafter the concrete has place.

8he operation commonly a &ste'process.


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+ethods of pre-tensioning

'$ :nchoring the tendons against the endabutments.

)$ Placing of 1ac2s.

0$ :pplying tension to the tendons.

$ Casting of concrete.

*$ Cutting of the tendons.

+ethods of post-tensioning '$ Casting of concrete.

)$ Placement of tendons.

0$ Placement of the anchorage bloc2 and 1ac2.

$ :pplying tension to the tendons. *$ =eating of the wedges.

$ Cutting the tendons.


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Popular post-tensioning system

'$ "reyssinet system


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)$ +agnel blaton system


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0$ iDord-udall system


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$


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Section for Pre-tensioning

ect"on for Post&tens"on"ng


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:d,antages of pre-stressedconcrete. "actory products are possible.


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3isad,antages of pre-stressedconcrete.

;eAuired s2illed builders E experienced engineers. Initial eAuipment cost is ,ery high.

:,ailability of experienced engineers is less.

;eAuired complicated formwor2.

It reAuires high strength concrete E steel. Pre-stressed concrete is less 7ber resistant.


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