Post tensioned (PT) slabs

The presentation contains:
The initial idea of the PT slab, Sustainable Construction with Post-Tensioned Slabs, Opportunities for the use of post-tensioning, What is post-tensioning, Comparison Between RC & PT slab, Why use post-tensioning slab, Post-tensioning market, Case Studies.

1. Post-tensioned (PT) slabs
A PRESENTATION ON
Department of
Civil Engineering.
Leading University, Sylhet

2. Presented by
FOYSOL MAHMUD
Batch: 10
th
;Section: B
Department of
Civil Engineering.
Leading University, Sylhet

3. Introduction
Post-tensioned(PT)slabsaretypicallyflatslabs.PTslabsofferthethinnestslabtype,
asconcreteisworkedtoitsstrengths,mostlybeingkeptincompression.Longer
spanscanbeachievedduetopre-stress,whichcanalsobeusedtocounteract
deflections.
Post-tensionedslabsusehigh-strengthtensionedsteelstrandstocompresstheslabs,
keepingthemajorityoftheconcreteincompression.Thisgivesaveryefficient
structurewhichminimizesmaterialusagesanddecreasestheeconomicspanrange
whencomparedtoreinforcedconcrete.

4. Sustainable Construction with Post-Tensioned Slabs
Embodied Energy and Embodied Carbon
ResearchconductedfortheConcreteCentre
hashighlightedthatthedifferencebetween
framesystemsisnotsubstantial.This
researchalsodemonstratedthatcarbon
savingsaremoresignificantlyinfluencedby
howthedesignandspecificationare
optimizedratherthanthechoiceofframing
material.
carefullydesignedandspecifiedpost-
tensionedframesolutionscanofferthelowest
achievablelevelsofembodiedCO2for
minimumdepth.

5. Opportunities for the use of post-tensioning
Resource efficiency
Typically 20% reduction in concrete volume.
The reinforcement requirement of a typical PT slab is 40% of the equivalent RC slab.
Carbon/Low Waste
100% secondary aggregate is also viable.
Reinforcing bar itself is typically from 95-100% recycled sources while the strand
content may be as much as 30% recycled.
Flexibility and Adaptability
Allow high thermal mass.
Long spans allow for future flexibility and adaptation.

6. What is post-tensioning?
Concretehasahighcompressivestrength,buthaslowtensilestrength.Traditional
reinforcementisoftenusedtogiveconcretemoreductilitybecausethesteelresists
thetensileforcesintheelement.Inpost-tensionedstructureshigh-strengthsteelis
used,whichistensionedagainsttheconcrete.Thisputstheconcreteinto
compression,utilizingmoreoftheinherentstrengthandenablingthinnerconcrete
sectionstobeused.

7. Simple Concept:
Post tension is a magic that holds slab against it’s direction
of deflection

8. Comparison Between RC & PT slab
•Based on span depth ratio
Floor System
Typical span Depth ratio
PT RC
OneWay 48 21-28
Two Way 45 33
One Way slab with drop panel 50 36

9. Comparison Between RC & PT slab
•Based on Costing
Bay
size
Slab Thickness
Rebar per sft
area
PT steel per sft
area
Cost per sftarea
(U$)
PT RC PT RC PT RC PT RC
30’x30’8in 10in 0.8 kg2 kg 0.5 kg0 8.05 9.56

10. Why use post-tensioning slab?
•Long-spans–post-tensionedconcretecanspanfurtherthanreinforcedconcreteand
competeseconomicallywithsteelstructures.Longspansreducethenumberofcolumnsand
foundationsandincreaseflexibilityforspace-planning.
•Minimumfloorthickness–Post-tensioninghastheminimumstructuralthicknessofanyfloor
system.Thisreducesself-weightandtheoverallheightofthebuilding.
•Openings–post-tensionedslabscanreadilyaccommodateopenings.Smallerholescanbe
formedbetweentendons,andlargerholescanbedesignedintothesystem.
•Performance–post-tensioningcomeswithallthebenefitsofconcretesuchasgoodvibration
control,fireresistanceandsoundinsulation.
•Sustainable–Thethermalmassoftheconcretecanbeutilisedtomoderatethetemperature
fluctuationsinthebuilding.Posttensioningalsoreducesthematerialsusedinthestructure.
Longerspansofferfutureflexibility–increasingthepotentiallife-spanofthebuilding.

11. Post-tensioning market
Theuseofpost-tensioning(PT)has
increaseddramaticallyoverthelast
decade.Therearenowmanycompanies
whichofferpostntensioningsupplyand
installationservicesinmanycountries.

12. Some Case Studies
Whitmore High School, UK
The new 9,550m² secondary school building has
been constructed with three storeystructure has
300mm thick PT slabs.
WhitestownWayShoppingCentre,Dublin
OriginallyconceivedasRC,thedecisionto
switchtopost-tensionedconcretehassaved
inexcessof€1M,principallyinreduced
reinforcedtonnage,decreasedconcrete
volumesandsimplifiedformwork.

13. Some Case Studies
MotorCity-Dubai-U.A.E.
ADGvalueengineeredafoundationalternativefor
thismixeduseresidentialdevelopmentinDubai.The
PostTensionedRaftsystemwasthefirstpurelyPT
rafttobeapprovedbyDubaimunicipality.The
superstructuredesignwascompletedbyADG,being
constructedwithsome2500tonsofposttensioning
Morrison’s Distribution Warehouse
Key Facts:
•Total area of ground slab, 42000 sq.m
•A 180mm thick flat slab was used.
•Significant reduction in construction joints and movement
joints.
•Superior control of concrete shrinkage and durability .

14. How it works….!

15. References
•The Structural Engineer: Volume 90, issue 5, may 2012, pp32-40
•www.pta.uk.com
•The post tensioning Association, GN04
•The post tensioning Association, GN03