PRESENTATION ON PRESENTATION ON POST TENSIONED FLAT SLABPOST TENSIONED FLAT SLAB

RCC > PRESTRESS?RCC > PRESTRESS?

-- Concrete structures were common by 1920Concrete structures were common by 1920’’ss

-- Concretes strength in compression and lack in tension was known.Concretes strength in compression and lack in tension was known.In RCC reinforcement replaces tension.In RCC reinforcement replaces tension.

-- Thus transformation is due to development of cracks Thus transformation is due to development of cracks -- VisibleVisible-- Not so visibleNot so visible

-- This leads to :This leads to :-- Loss of durability due to cracking Loss of durability due to cracking

-- Substantial deformations due to loss in section propertiesSubstantial deformations due to loss in section properties

This restricted the use to smaller spansThis restricted the use to smaller spans

HISTORY OF PRESTRESSINGHISTORY OF PRESTRESSING

Initial Research and Development in Europe 1928Initial Research and Development in Europe 1928--1933.1933.

PioneersPioneers : : -- Freyssinet Freyssinet -- FranceFranceLeonhardtLeonhardt -- GermanyGermanyMagnelMagnel -- BelgiumBelgium

USA adopted this technology in 1949.USA adopted this technology in 1949.

Reason for Development : Inability to increase spans of RCC Reason for Development : Inability to increase spans of RCC Bridges.Bridges.

First Bridge First Bridge : : -- Choicy Le Ruy across Seine Choicy Le Ruy across Seine Paris 1935 span 40m.Paris 1935 span 40m.

Prestressing is a tested, knowledge based Technology which has withstood TEST OF TIME.

Live Technology : - Continuous State of Development. Better, Stronger and improved Materials With matching Hardware.

2000T Capacity single Systems with steel strands.

1 T Capacity Carbon Fibre systems in Rehabilitation field

FROM BRIDGES TO PT SLABSFROM BRIDGES TO PT SLABS

Prestress Developed initially for long span bridges.Prestress Developed initially for long span bridges.First span was 40m. Now 1000m spans are planned First span was 40m. Now 1000m spans are planned using cable stay technique which has same basic using cable stay technique which has same basic principles, materials, hardware.principles, materials, hardware.Technology was adopted later for many long span Technology was adopted later for many long span

structures like aircraft hangers.structures like aircraft hangers.Initial developments were all in Post Tensioning. Initial developments were all in Post Tensioning.

-- i.e.. Concrete cast first and prestress applied later.i.e.. Concrete cast first and prestress applied later.

Later Pre Tensioning developed.Later Pre Tensioning developed.-- i.e.. Concrete is cast around wires/strands already i.e.. Concrete is cast around wires/strands already

tensioned .tensioned .-- initially applied for standardized bridge girders. initially applied for standardized bridge girders. -- Then to precast building slabs and precast girders. Then to precast building slabs and precast girders.

Advantages of PreTensioningAdvantages of PreTensioning---- Product uniformity factory made. Product uniformity factory made. ---- Quick turnover with fast curing techniques.Quick turnover with fast curing techniques.

DisadvantagesDisadvantages---- Transport, handling, multiple joints.Transport, handling, multiple joints.---- Profiling limitations hence span restrictions.Profiling limitations hence span restrictions.

To Overcome above post tensioning of slab To Overcome above post tensioning of slab developed.developed.

AdvantagesAdvantages---- Reduction in number of joints Reduction in number of joints ---- Mass poursMass pours---- Quick removal of shutter possible to achieve same Quick removal of shutter possible to achieve same speedspeed

Developed initially in USA.Developed initially in USA.

Being in use for last 50 years in various countries.Being in use for last 50 years in various countries.

In Asian countries like Singapore, India in use for last 35 In Asian countries like Singapore, India in use for last 35 years.years.

In middle east last 15In middle east last 15--18 years18 years

In Oman last 5In Oman last 5--6 years6 years

Oman therefore is starting withOman therefore is starting with---- 50 years of knowledge 50 years of knowledge ---- Benefits of all theoretical research and development.Benefits of all theoretical research and development.---- Benefits of hardware development during periodBenefits of hardware development during period..

WHEN & WHY PT SLABS?WHEN & WHY PT SLABS?New buildings requireNew buildings require

Large span structures, with flexible plansLarge span structures, with flexible plansUnobstructed space below sofit for servicesUnobstructed space below sofit for servicesBuilding height regulations : optimisation of storey htBuilding height regulations : optimisation of storey ht

Possible only if Possible only if

Beam less system is developed. Beam less system is developed. 1) rcc flat slab 1) rcc flat slab 2) prestressed flat slab2) prestressed flat slab

It is also possible to have It is also possible to have prestressedprestressed slabs in normal slabs in normal slab and beam system, also allowing larger slab slab and beam system, also allowing larger slab spans.spans.Special Hardware suitable for slabs has been Special Hardware suitable for slabs has been

developeddevelopedFlat SheathingsFlat Sheathings20mm 20mm thkthk 45 to 70 mm wide for 12.7mm strand45 to 70 mm wide for 12.7mm strand

----RigidRigid----FlexibleFlexible

Flat AnchoragesFlat Anchorages

12.7 mm HT Strand

Flat GI Duct

Flat Anchorage

Grout Vent Tube

5 Strand Anchorage

3 Strand Anchorage

FLAT ANCHORING SYSTEMFLAT ANCHORING SYSTEM

Design Design ACI ACI : 318: 318ACI ACI : 423 For unbonded tendons : 423 For unbonded tendons CAN CAN : A23.3: A23.3BS BS : 8110 : 8110

MaterialsMaterialsPrestressing strandsPrestressing strands

ASTM : A416, A421 ,A776ASTM : A416, A421 ,A776BS : 5896BS : 5896

APPLICABLE CODESAPPLICABLE CODES

ConcreteConcrete : Minimum C30 generally C35: Minimum C30 generally C35--C40C40

Reinforcing steelReinforcing steel : Based on country wise availability: Based on country wise availabilityIn OmanIn Oman :: 460 n/mm460 n/mm22

In IndiaIn India :: 415 n/mm415 n/mm22

:: 500 n/mm500 n/mm22

In SingaporeIn Singapore :: 500 n/mm500 n/mm22

Prestressing steelPrestressing steel : Normal relaxation steel or grade I : : Normal relaxation steel or grade I : braking Load braking Load ~ ~ 1750 n/mm1750 n/mm22

: Low relaxation steel or grade II or : Low relaxation steel or grade II or super grade super grade ~ ~ 1860 n/mm1860 n/mm22

MATERIALS USED IN PT

SheathingSheathing : : GalvanisedGalvanised IronIronBright MetalBright MetalHDPE (Common in bridges).HDPE (Common in bridges).

GroutGrout : Basic cement , water mixture with : Basic cement , water mixture with admixture to fill the space between admixture to fill the space between sheathing and strands.sheathing and strands.Grade should be same as concrete Grade should be same as concrete slab slab

COMPARISON OF RCC AND PRESTRESSEDCOMPARISON OF RCC AND PRESTRESSEDFLAT SLABFLAT SLAB

RCC Flat SlabRCC Flat Slab

1.1. Cracked section under service.Cracked section under service.2.2. Excessive deformations or Excessive deformations or

increased thickness to control increased thickness to control deformations, due to cracked deformations, due to cracked sections.sections.

3.3. Once cracked no closure of Once cracked no closure of crack removal of load.crack removal of load.

4.4. Heavy reinforcement leads to Heavy reinforcement leads to conjustion and concretability conjustion and concretability parameters. parameters.

Prestressed Flat SlabPrestressed Flat Slab

1.1. Uncracked section under service.Uncracked section under service.

2.2. Deflections very much under Deflections very much under limit due to :limit due to :a) a) Prestress gives opposite initial Prestress gives opposite initial

deformationsdeformationsb) Gross properties reduce b) Gross properties reduce

deflections deflections

3.3. Due to positive force on section Due to positive force on section closure on removal of load.closure on removal of load.

4.4. No conjustion of steelNo conjustion of steel..

COMPARISON OF RCC AND PRESTRESSEDCOMPARISON OF RCC AND PRESTRESSEDFLAT SLABFLAT SLAB

RCC Flat SlabRCC Flat Slab

55 Excessive shrinkage cracks.Excessive shrinkage cracks.

6.6. Shear performance Shear performance --Normal.Normal.

PrestressedPrestressed Flat SlabFlat Slab

5.5. Early stressing of part of cables Early stressing of part of cables reduce these substantially.reduce these substantially.

6.6. Since section is uncracked and Since section is uncracked and compressed enhanced shear compressed enhanced shear capacity by 30% or so.capacity by 30% or so.

RCC flat slabRCC flat slab

1.1. Slab thickness 300mmSlab thickness 300mm

2.2. HYSDHYSD 35 to 40 kg/m35 to 40 kg/m22

depending on size of dropcapdepending on size of dropcap

3.3. HTSHTS NilNil

4.4. Likely long term deflection Likely long term deflection 2828--30mm30mm

Prestressed flat slabPrestressed flat slab

1.1. Slab thickness 220mmSlab thickness 220mm

2.2. HYSD 8 HYSD 8 –– 10 kg/m10 kg/m22

depending depending on dropcapon dropcap

3.3. HTS ~ 4.5 kg/mHTS ~ 4.5 kg/m22

4.4. Likely long term deflection Likely long term deflection 1010--12mm12mm

COMPARISON OF RCC & PT FLAT SLAB ON REAL PARAMETERS

Take typical 9m x 9m grid Live load 4kn/m2 SDL 3 kn/m2

Cost ComparisonCost ComparisonProject :Sohar Pearl

Alternative 1 : RCC Flat Slab Alternative 1 : RCC Flat Slab

For 8.5 x 8.3M Grid For 8.5 x 8.3M GridSlab thickness 300 MM Slab thickness 300 MMDrop Cap 4000*4000*450MM Drop Cap 4000*4000*500MM

Materials Q uantity Unit Price Amount Materials Q uantity Unit Price AmountConcrete 25.565 36.000 920.340 Concrete 24.365 36.000 877.140

Reinforcemen 2556.5 0.380 971.470 Reinforcement 2436.5 0.380 925.870Shuttering 71.75 5.800 416.150 Shuttering 72.15 5.800 418.470

Total RO : 2307.960 Total RO : 2221.480

Alternative 2 : Post-tensioned Slab Alternative 2 : Post-tensioned SlabFor 8.5 x 8.3M Grid For 8.5 x 8.3M GridSlab thickness 200 Slab thickness 200 MMDrop Cap 2800*2800*350 MM Drop Cap 2800*2800*350 MM

Materials Q uantity Unit Price Amount Materials Q uantity Unit Price AmountConcrete 15.2 36.000 547.200 Concrete 15.2 36.000 547.200

Reinforcemen 634.95 0.380 241.281 Reinforcement 634.95 0.380 241.281Shuttering 71.39 5.800 414.062 Shuttering 71.39 5.800 414.062

Post-tensionin 70.55 9.000 634.950 Post-tensionin 70.55 9.000 634.950

Total RO : 1837.493 Total RO : 1837.493Savings 20.4% Savings 17.3%

O ffice & Apparment Buildings City Mall

••Large floor area can be tackled at a timeLarge floor area can be tackled at a time••Reduction in overall construction timeReduction in overall construction time

Less concrete volume per Less concrete volume per pourpour

••Early formwork release.Early formwork release.••Reduction in total construction time.Reduction in total construction time.••Reduction of formworks sets.Reduction of formworks sets.••Improvement in constructability. Improvement in constructability. –– table forms.table forms.

Quick rotation of formwork Quick rotation of formwork

••Easier placing and handling of reinforcementEasier placing and handling of reinforcementReduction of steel Reduction of steel reinforcement and reinforcement and arrangement simplificationarrangement simplification

CO

NST

RU

CT

ION

CO

NST

RU

CT

ION

••Improvement in serviceability for all nonImprovement in serviceability for all non--structural elements.structural elements.High deflection controlHigh deflection control

••Improvement in durability Improvement in durability ••Improvement in slab rigidity Improvement in slab rigidity

Limitation on crack widthsLimitation on crack widths

••Increase in column of free space Increase in column of free space ••Flexible planningFlexible planning

Large spansLarge spans

••Floor to floor height reductionFloor to floor height reduction••Savings on total building height 1 floor can be gained for approSavings on total building height 1 floor can be gained for approx. each x. each 20 floors20 floors••Reduction of slab thickness leads to reduced energy needsReduction of slab thickness leads to reduced energy needs••Savings in columns and foundations costs Savings in columns and foundations costs ••Reduced formwork costsReduced formwork costs

Reduction in slab thicknessReduction in slab thickness

DE

SIGN

DE

SIGN

Related further advantagesRelated further advantagesDirect advantageDirect advantage

If drop cap not available : Punching shear If drop cap not available : Punching shear problems.problems.

or inadequate or inadequate Limitations on max. shear Limitations on max. shear even with reinforcement.even with reinforcement.

RCC and PT Junctions.RCC and PT Junctions. Openings.Openings. Shrinkage cracking.Shrinkage cracking. Multi level propping.Multi level propping. Honeycombing near anchorages.Honeycombing near anchorages. Breakage at passive anchorsBreakage at passive anchors..

CRITICAL ISSUES : AS DESIGNERCRITICAL ISSUES : AS DESIGNER

Examples of punching shear reinforcement for Examples of punching shear reinforcement for flat slabflat slab

Design of scaffolding system.Design of scaffolding system.

When can shutter be released?When can shutter be released?

Multilevel proppingMultilevel propping

CRITICAL ISSUES : AS CONSTRUCTORCRITICAL ISSUES : AS CONSTRUCTOR

SHARING OF DESIGN RESPONSIBILITIESSHARING OF DESIGN RESPONSIBILITIES

Globally ,PT is operated through special Agencies who have to Globally ,PT is operated through special Agencies who have to act in cooperation with main consultant and main contractoract in cooperation with main consultant and main contractor..

Necessary to DEFINE ResponsibilitiesNecessary to DEFINE Responsibilities..

Framing Plan, Column Spacing Framing Plan, Column Spacing -- Main RCC consultant /Main RCC consultant /Architect / OwnerArchitect / Owner

Global Analysis including Global Analysis including Lateral load analysis Lateral load analysis Columns, footings, RCC areasColumns, footings, RCC areas --Main ConsultantMain ConsultantLoad bearing beamsLoad bearing beamsAdditions in slab for Global effects Additions in slab for Global effects

Slab Analysis ( Vertical Loads Only)Slab Analysis ( Vertical Loads Only)-- PT ConsultantPT Consultant

Slab Drawings :Slab Drawings :PT Layout & ElevationsPT Layout & Elevations -- PT ConsultantPT ConsultantReinforcement in slabsReinforcement in slabs

Overall stability of structureOverall stability of structure -- Main ConsultantMain Consultant

SHARING OF DESIGN RESPONSIBILITIESSHARING OF DESIGN RESPONSIBILITIES

Procedures /Work MethodologyProcedures /Work Methodology

StepStep--01: Tendon &Anchorage Installation01: Tendon &Anchorage InstallationStepStep--02:Concreting/Casting of Slab02:Concreting/Casting of SlabStepStep--03: Stressing of Cables03: Stressing of CablesStepStep--04: Grouting of Cables04: Grouting of Cables

Step -01 : Tendon & Anchorage Installation

Step-02: Concreting /Casting of Slab

Step-03: Stressing of Cable

Step-04: Grouting of Tendon

Ongoing and Completed ProjectsOngoing and Completed Projects

Project: Al Rawaq Building

Client: Suhail Bahwan Holdings

Consultant: Cowi & Partners LLC

Project: ASSAUD Business Centra

Client: Alia Properties

Consultant: Triad Oman Consultants

Project: 4 star Hotel Appartment at Al Qurum

Client: Mustafa Sultan Enterprises

Consultant: Al Hatmy Consultants

Project: Proposed Hotel Development at Azaiba

Client: Azaiba Hotel LLC

Consultant: Kadri Consultants

Project: Knowledge Oasis Muscat-04

Client: PIEI

Consultant: NEO/EIDC

Project: Comm Bldg at MBD for Badrr Shipping

Client: Badrr Shipping Agencies

Consultant: EIDC

Project: Facility Building at KOM

Client: Oasis Development SAOC/PIEI

Consultant: Leeyanah Engg Consultancy

Project: Headquarters for MOD-Pension Fund

Client: MOD-Pension Fund

Consultant: Gulf Engg Consultancy

Project: Al Ruwad International School

Client: Muscat Int School

Consultant: Gulf Engg Consultancy

Project: Muscat International Airport-PkgIII

Client: Ministry of Transport& Communication

Consultant: Hill International

Contractor: Bechtel Enka Bahwan Consortium

Project: Comm Bldg at Bausher for Sk Salem Al Areimi

Client: Sk Salem Al Areimi

Consultant: TRIAD Oman

Project: Bait Al Zubair –Ph04

Client: The Zubair Corporation

Consultant: Image Design/TRIAD Oman

Project: Residential development at Ruwi

Client: The Zubair Corporation

Consultant: NEO

Project: Residential development at Wadi Kabir

Client: Sk Salem Al Areimi

Consultant:TRIAD Oman

Project: Residential Building –Dar Al Maha-01

Client: Sohar Investment & Development

Consultant: EIDC

Project: Comm Res Bldg for Mr Dawood Al Futaisi

Client: Mr Dawood Al Futaisi

Consultant: Dawood Consultancy

Project: The Sultan centre at Azaiba

Client: The Sultan centre

Consultant: Cowi & Partners

Project: Al Maha Beach Restautant

Client: Al Rotana Hotels & Developments

Consultant: EIDC

PT Slab ready for Concreting

PT Slab & PT Beam

PT Slab Before Concreting

Beamless Slab Soffit

PT Slab with Column Heads/Drop Caps

THANK YOU THANK YOU ……

Corporate AddressSpecialised Engineering LLCPO Box 1020,Ruwi-112Sultanate of OmanTel: 24713494Fax:24713495E-mail-info@spl-eng.comWeb:www.spl-eng.com