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SEMINAR ON

Construction Aspects of Post-Tensioned Flat SlabGuided by- Prof. Patil V S Prof. Khurth V GPresented By

Mr. Mulla Amanulla Liyakatali

Session Outline Quick review of basic prestressing

technique General applications of prestressing What is PT flat slab & its Types Construction aspects &materials Used

in PT flat slab Benefits over conventional RCC slab Discussion References

What Is Prestressing???? Prestressing is process of subjecting member

under compressive stresses (compression) by external longitudinal loading.

Also.Prestressed concrete can most easily be defined as precompressed concrete. This mean that compressive stress is put into concrete member before begin its working life and its position to be in areas where tensile stress develop under working load.

Prestressed Concrete vs. RCCThe main difference between PC and RC is the fact that steel reinforcement in the Prestressed Concrete is ACTIVE and the same is PASSIVE in Reinforced Concrete

Types of Prestressing.

Pre-tensioning Post-tensioning-

What is Pre-tensioning???Steel reinforcement are stressed prior to concrete placement, usually at a precast plant remote from the construction site. How Pre-tensioning is done ???

What is Post-tensioning ???Steel tendons are stressed after the concrete has been placed and gained sufficient strength at the construction sites. Example : Post Tensioning of Floor Slab,

How Post-tensioning is done ???

STRESSING AFTER CASTING

Post-Tensioning System-

Application of Prestressed Concrete

COMMERCIAL / INDUSTRIAL FLOORS

SLAB ON GROUND

Buildings

What is PT Slab ???

The slab constructed with posttensioning technique and having top and bottom surfaces parallel to each other.

Types of Flat Slab

STEPS IN CONSTRUCTION OF PT SLAB AND MATERIALS

Stages in formwork and reinforcementShuttering Marking Profiling

Layout

Elevation

STEEL PROPS

ADJUSTABLE SPANNING

PLACING OF BOTTOM REINFORCEMENT

POSITION OF CHAIRS FOR PROFILING OF TENDONS

Profiling

LayoutSetting out of the cable profile, spacing of strands.

ElevationIt is the arrangement of Duct/strands +ve and ve moment.

PLACING OF TOP REINFORCEMENT

LIVE END BLOCK REINFORCEMENT

BALLOONING AT DEAD END

DEAD END R/F

STRANDS USED FOR BONDED PT CONSTRUCTION

STRANDS USED FOR UNBONDED PT CONSTRUCTION

IDENTIFICATION OF TENDONS

PLASTIC DUCTS

STEEL DUCTS

FLAT DUCTS RESTED ON CHAIRS

MONOSTRAND ANCHORS FOR UNBONDED P T

MULTISTRAND ANCHORS FOR UNBONDED P T

POSITIONS OF COMPONENTS

SHEAR RESESTING STUDS

CONCRETING OF SLAB.Before casting, some precautions are taken such as checking the sheath joints and connection of grouting vents.

To minimize manual errors in casting and compaction, equipments like concrete pumps, surface compactor, Needle Vibrator are used.

Pumping Unit

Mixing Unit

Batching Uni

CONCRETE MIXING PLANT

CONCRETING

REMOVE POCKET FORMER

CLEAN THE STRANDS

MARK THE TENDONS

STRESS TENDONS

MEASURE ELONGATION

E.O.H PUMPThis is used to give hydraulic pressure to the jack. Gauge-1:- used to control pressure of the jack.

Gauge-2:- used to block the strand into the jack.

CLEAN END PACKETS

PATCH END POCKETS

Grouting

MachineFeeding Unit

Controlling Unit

Grout Mixer & Collection Unit

Control Valves

Pump

Supply Pipe

REDUCED SHORING COST

GEOMETRIC FLEXIBILITY

Reduced construction cost Faster construction Elegant structure Improved Water resistant Early formwork stripping Floor to floor height reduction Reduced foundation load Improved deflection control Greater column free areas Reduced seismic risk Flexible planning Reduced cladding cost

BENEFITS OF FLAT SLAB

HOW CONSTRUCTION IS FASTER?

HOW SECTION SIZES GET REDUSED ?

Post-tensioning reduces overall building mass, which is important in zones of high seismicity.

Profiled tendons result in balanced gravity loads, significantly reducing total deflections.Permanent compressive forces result in greater control of cracks, deflection, and camber.

The flat-plate building clearly behaves like the strong column-weak beam mechanism

DISCUSSIONSComparative cost of PT & RCC durability of structure. innovative technique and the unavailability of materials and if PT slab get implemented on large scale which ultimately increase demand of materials resulting in production of PT materials. And the material will be easily available If we observe todays situation which is exactly in favors of PT construction that is the number of companies entering in the production of PT materials is going on increasing. Resulting in the lesser cost of material which affects the economics of PT. Also due to advanced portable stressing equipment and sophisticated design software helping in complex tendon profile and rigorous reinforcement details promoting the construction of PT and maximizing the use of todays engineering skill.

11.0 REFERENCES

ONLINE REFERENCES: http://www.pci.org http://pubs.asce.org/books/ http://www.bassbeams.co.za http://www.sciencedirect.com/ http://www.bbrnetwork.com http://www.vsl.net http://www.gostructural.com http://enr.construction.com http://www.noorps.com http://www.structureae.de.com http://www.wisegeek.com http://www.tech9.in http://www.concretenetwork.com http://www.infolink.com.au http://www.ntpholdings.com/project s.asp http://www.cclstressing.com/ http://www.yde.co.il/ http://www.conforce.co.uk/ http://www.istructe.org.uk/

OFFLINE REFERENCES:

BOOKS Prestressed concrete by krishnaraju Prestressed concrete by Dayaratnam Modern prestressed concrete by James R.Libby. STANDARD CODES IS: 1343 for prestressed concrete ACI 318-77 ACI Standard building code requirements for reinforced concrete. CP 110: Part I: 1972 Code of practice for the structural use of concrete: Part I Design, materials and workmanship. AS 1481-1974 SAA Prestressed concrete code. Standards Association of Australia.

RESOURSES