SEMINARON

“Construction Aspects of Post-Tensioned Flat Slab”

Presented By

Mr. Mulla Amanulla Liyakatali Department Of Civil Engineering

Sanjay Ghodawat Institute, Attigre

Guided by- Prof. Patil V S Prof. Khurth V G

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

Prestressing is process of subjecting member under compressive stresses (compression) by external longitudinal loading.

Prestressing is process of subjecting member under compressive stresses (compression) by external longitudinal loading.

What Is Prestressing????

Prestressed Concrete vs. RCC

The 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

Prestressed concrete can most easily be defined as pre-compressed 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.

Also….

Types of Prestressing.

Post-tensioning-

Pre-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 post-tensioning technique and having top and bottom surfaces parallel to each other.

Types of Flat Slab

STEPS IN CONSTRUCTION OF PT SLAB AND

MATERIALS

Shuttering

Marking

Layout Elevation

Profiling

Stages in formwork and reinforcement

ADJUSTABLE SPANNINGSTEEL PROPS

PLACING OF BOTTOM REINFORCEMENT

POSITION OF CHAIRS FOR PROFILING OF TENDONS

Elevation

Profiling

Layout

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

Setting out of the cable profile, spacing of strands.

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

MONOSTRANDANCHORS 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.

CONCRETE MIXING PLANT

Mixing Unit

Batching Unit

Pumping Unit

CONCRETING

REMOVE POCKET FORMER

CLEAN THE STRANDS

MARK THE TENDONS

STRESS TENDONS

MEASURE ELONGATION

E.O.H PUMP- This 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 Machine

Grout Mixer &Collection Unit

Supply Pipe

Control Valves Pump

Feeding Unit

Controlling Unit

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 loadImproved deflection control Greater column free areasReduced seismic riskFlexible planningReduced cladding cost

BENEFITS OF FLAT SLAB

HOW CONSTRUCTIONIS 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

Comparative cost of PT & RCCdurability of structure. innovative technique and theunavailability 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 today’s 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 today’s engineering skill.

DISCUSSIONS

11.0 REFERENCES

ONLINE REFERENCES:http://www.pci.orghttp://pubs.asce.org/books/http://www.bassbeams.co.zahttp://www.sciencedirect.com/http://www.bbrnetwork.comhttp://www.vsl.nethttp://www.gostructural.comhttp://enr.construction.comhttp://www.noorps.comhttp://www.structureae.de.comhttp://www.wisegeek.comhttp://www.tech9.inhttp://www.concretenetwork.comhttp://www.infolink.com.auhttp://www.ntpholdings.com/projects.asphttp://www.cclstressing.com/http://www.yde.co.il/http://www.conforce.co.uk/http://www.istructe.org.uk/

OFFLINE REFERENCES:

BOOKSPrestressed concrete by krishnarajuPrestressed concrete by DayaratnamModern prestressed concrete by James

R.Libby.STANDARD CODES IS: 1343 for prestressed concreteACI 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