IRC: 18-2000

DESIGN CRITERIAFOR

PRESTRESSEDCONCRETE ROADBRIDGES

(POST-TENSIONEDCONCRETE)

(Third Revision)

THE INDIAN ROADS CONGRESS2000

IRC: 18-2000

DESIGN CRITERIAFOR

PRESTRESSEDCONCRETE ROADBRiDGES

(POST-TENSIONED CONCRETE)

Pvbliihedbym nmwrR~AD0CONGRESSJ~~r flouts,SbakjabaaRoad,

NowDelhi-i100112180

P11ccRsI2S~(PbspacMng &poitage)

IRC 1 8~2000

First publishedReprintedReprintedFirst RevisionReprintedSecondRevis ionReprintedReprintedThird Revision

December,1965October, 1969Febniary, 1974January,1977July, 1983 (with Notationsandunits as per IRC 71)November,1985September,1990[)ecember,1997 (with latestamendments)October,2000

(Rights(~fPublication and of Translation are rcservea)

Printed at Dee Kay Printers,New Delhi-I 100151000 Copies- October, 2000

IRC: 18-2000

CONTENTSPageNo.

Compositionof Bridge Specifications& StandardsCommittee (i) to (ii)Notations (iii) to (v)Clause No.

I Introduction2. Scope 23 Materials 34, Concrete 75. LoadsandForces 76. StagePrestressing 87, PermissibleStressesin Concrete 88. PermissibleStressesin PrestressingSteel 119. SectionProperties 1110, Moduli of Elasticity 14ii. Lossesin Prestress 1512. Ultimate Strength 2013. Calculation of Ultimate Strength 2014. ShearandTorsion 21IS Minimum Reinforcement 3016. Cover and Spacingof PrestressingSteel 3217. End Blocks 3418. Thickening of Webs of Girders. 3719. Anchorageof Cablesand Stressing 3720. Splay of Cables in Planand Minimum Radiusof

Cables in Elevation 3721. SlenderBeams 3822. EmergencyCables/Strands 3823. Storageand Handling of Prestre.ssingMaterials 3824. PrestressingOperation 3825. Grouting of Cables 38

AppendicesIA. Testson SheathingDucts 39113. Tests on CorrugatedHDPE SheathingDucts 452. Specificationfor SheathingDuct Joints 483. RecommendedPracticefor Storagesand Handling of

PrestressingMaterial 504. RecommendedPracticefor PrestressingOperations 515. RecommendedPracticefor Grouting of Post-Tensioned

Cablesin PrestressedConcreteBridges 52

1RC: 18-2000

MEMBERS OF THE BRIDGE SPECIFICATIONS ANDSTANDARDS COMMITTEE

(As on 7.12.99)

I. Prafulla Kumar*(Convenor)

2. The Chief Engineer(B)S&R (Member-Secretary)

3. SS.Chakra¼wty

4. Dr. MG. Tamhankar

5. Ninan Koshi

6. AG. Borkar

7. N.K. Sinha

8. M.V.B. Rao

9. CR. Alimchandani

10. Dr. S.K. Thakkar

11. M.K. Hhagwagar

PD. Wani

S.A. Reddi

14. VijayKumar

15. CV. Kand16. M.K. Mukheijee17, Mahesh Tandon

18. Dr,T.N.SubbaRao

19. AK. }Iarit

20. A.D. Narain

21. V.R.Jayadas

22, P.C.Bhasin

DG(RD) & AddI, Secretary,Ministry of Surface Transport(Roads Wing), TransportBhawan, New Delhi-I 10001(V. Velayutham). Ministry ofSurface Transport(Roads Wingh), TransportRhawan, New Delhi-il 0001Managing Director, Consulting Engg. Services (I) Ltd., 57,NehruPlace,New Delhi-I100l9Emeritus Scientist,StructuralEngg. Res. Centre,399, PocketE, Mayur Vihar PhaseII, Delhi-l10091DG(RD) & Addl. Secretary(Retd.), 56, Nalanda Apartments,Vikaspuri,New DelhiTechnicalAdviser to Metropolitan Cornmr., A-I, SusnehiPlotNo. 22, Arun Kumar Vaidya Nagar, Sandra Reclamation,Mumbai-400050Chief Engieer (PlC), Ministry of Surface Transport(RoadsWing), TransportBhawan,NewDelhi-i 10001Head,Bridge Division, Central Road ResearchInstitute, P.O.CRRI, NewDelhi-I 10020Chairman & Managing Director (STUP Consultants Ltd.,1004-5, Raheja CI~ambems,213, Nariman Point, Mumbai-400021Professor, Departmentof EarthquakeEngg., University ofRoorkee,Roorkec-247667Consulting Engineer,Engg. Consultants(P) Ltd., F-l4/15,Connaught Place,NewDelhi-I 10001Member, MaharashtraPublic ServiceCommission, Bank ofIndia Building, Mumbai-400025Dy. Managing Director,GammonIndia Ltd.Gammon House,Prabhadevi,Mumbai-400025ManagingDirector, UP State Bridge Corporation Ltd., SeWBhavan,16, MadanMohanMalviya Marg, Lucknow-226001Consultant,E-21136,MahavirNagar, Bhopal-46201640/182,CR. Park,NewDelhi-I 10019Managing Director, Tandon Consultants(P) Ltd., 17, LinkRoad,Jangpura,Extn., New DelhiChairman,ConstrumaConsultancy(P) Ltd., 2nd Floor, PinkyPlaza,Mumbai-400052Executive Director (B&S), ResearchDesigns& StandardsOrganisation,Lucknow-226001DirectorGeneral(RoadDevelopment)& Addl. Secy.,MOST(Retdj, B-186,Sector26,NOIDAChief Engineer, Dy. Director General (B), DGBR, SeemaSadakBhavan, Delhi Cantt,, Naraina,New Delhi-66324,Mandakini Enclave, Alkananda, NewDelhi-Il 0019

12.

13.

~ADG(B)beingnot in position. The meeting was presided by Shri Prafulla Kumar, DirectorGeneral(RoadDevelopment)andAddI. Secretary, Ministry of Surface Transport.

(i)

IRC: 18-2000

23. P,K.Sarmah

24. SR.Tambe

25. The Secretary to theGovt. of Gujarat

26. The Chief Engineer~R&B)

27. The Chief Engineer(NH)

28. The Engineer-in-Chief

29. The Director General(Works)

30. The Chief Engineer31. The Chief Engineer (K)

S&R32. The Director

33. The Director & Head

34. The Chief Engineer (NH)35. The Chief Engineer (NH)36. The Chief Engineer (NH)

37. PresidentIndian Roads Congress

38. Director General(Road Development)

39. Secretary,Indian RoadsCongress

1. N.V.Merani

2. Dr. G.P. Saha

3. Shitala Sharan

Chief Engineer, PWD (Roads) Assam, P.O. Chandman,Guwahati-781003Secretary,MaharashtraPWD (Retd.), 72, Pranit J. PalkarMarg,Opp.PodarHospital,Worli, Mumbai-400025(H.P. Jamdar)R&B Department,Block No. 14,NewSachivalaya,2nd Floor, Gandhinagar-382010(D. Sree Rama Murthy), NationalHighways, Irrum Marizil,HyderabadSOO482(D. Guha),Public Works Department, Writers’ Building, BlockC,Calcutta-700001(R.R. Sheoran), Haryana P.W.D., B&R, Sector-19 B,Chandigamh-i600l9CentralPublic Works Department,Nirman Bhawan,New Delhi

Ministry of Surface Transport (Roads Wing), NewDelhi(CC. Bhattacharya), Ministry of Surface Transport(Roads Wing), TransportBhawan, New DelhiHighways ResearchStation, 76 Sarthat Patel Road,Chennai-600025.Bureau of Indian Standards, Manak Bhawan, 9, BahadurshahZafar Marg, New Delhi-I 10002Mr. Public Works Department,Bhopal-46l004UP. P.W.D.,LucknowPunjabPWD, B&R Branch, Patiala

Ex-Offlcfo MembersK.B. RajonaEngineer-in-Chief Delhi, PWD,NewDelhiPrafulla Kumar,DG(RD) & Addi. Secretary to the Govt. of India,Ministry of Surface Transport(RoadsWing),TransportBhawan,NewDelhi-I 10001S.C. Sharma,Chief Engineer,Ministry ofSurface Transport(Roads Wing)TransportBhawan,NewDelhi-I 10001

CorrespondhtgMembersPrincipal Secretary(Retd.), A-47/l344, AdarshNagar,WorE, Mumbai-400083Chief Engineer, Hindustan Construction Co. Ltd.,Hincon House, Lal BahadurShastri Marg,Vikhroli (W), Mumbai-400083Advisor Consultant, Consulting Engg. Services(I) Pvt. Ltd.,57, Nehru Place, New Delhi-1100l9

(ii)

IRC: 18-2000

NOTATIONSArea of High Tensile Steel

A Area of longitudinal reinforcement

Cross-sectionalareaof two legs of a linkA : Area of connectorsteelA : Area enclosedby the centre line of membersforming a box

sectionA Bearingareaof the anchorageconvertedin shapeto a squareof

equivalentareaA, Maximum areaof the squarethat can be containedwithin the

memberwithout overlapping the correspondingarea of theadjacentanchorages,andconcentricwith thebearingareaWidth of a rectangularsection or rib of a Tee,L or I beam

b1 Sideof anchorplateWidth of flangeof Tee or L beam

il : Overall depthof the girdermeasuredfrom top of deck slab tothe soffit of girder

db : Depthof the girderfrom the maximumcompressionedgeto thecentreof gravity of the tendons

d, : Diameterof prestressingwire/strandDepthfrom extremecompressionfibre eitherto the longitudinalbars or the centroidof the tendons,whichever is greaterModulusof Elasticity of concreteat 28 daysModulus of Elasticity of prestressingsteel

E. : Modulusof Elasticity of Concreteat j days(j<28 days)e : Baseof NaperianLogarithmsF~, Bursting tensile force in endblock

Averagecompressivestressin flexural compressivezoneActual concretecubestrengthat j dayssubjectto a maximumvlaue of “~k (j<28days)

Characteristiccompressivestrengthof 15 cm cubesat 28 daysf Compressivestressat centroidalaxis due to prestresstaken as

positivePermissiblecompressivecontact stress in concrete includingany prevailingstressas in the caseof intermediateanchorages

f : Ultimate tensile strengthof prestressingsteelStressdueto prestressonly at the tensile fibre distance v’ fromthe centroidof the concretesection

(iii)

IRC: 18-2000

Maximum principal tensilestressin concreteThe characteristicstrengthof the untensionedsteelYield stressof longitudinal steel in compressionYield strength of longitudinal reinforcementor 0.2 per centproofstresswhich shouldbetakenas notgreaterthan415 MPaYield strengthof links/shearreinforcementor 0.2per centproofstresswhich shouldbe taken as not greaterthan 415 MPa

G : Dead loadH : Largerdimensionof the section

Smallerdimensionof the sectionh Wall thicknessof membersof box sectionwheretorsionalstress

is determined1 : Secondmomentof areaof the sectionk Wobble co-efficient per metre Length of prestressingsteel/ Length of specimenM : Bendingmomentat the sectionMPa : MegaPascalsMt : Crackingmomentat the concretesection consideredMlt : Moment of sectionunderultimate load conditionn : Numberof test strengthresults

Load in tendonQ : Designlive load including impactS Standarddeviation(Sample)SG SuperimposeddeadloadS1 : Spacingof connectorsS~ : Link spacingalong the length of a memberT : Torsionalmomentdueto ultimateloads

Thicknessof flangeof a Tee beamV Shear force at the sectionconsideredunder ultimate loads,

actualvolume of waterPremeasuredquantity of waterBalancequantity of water left

V : Ultimate shear resistanceof a concretesectionV : Ultimate shearresistanceof a concretesection uncrackedin

Co

flexureVolume of sheathingsampleusedin water lossstudyUltimate shear resistanceof a concrete section, cracked inflexure

(iv)

IRC: 18-2000

Torsional shear stress in concrete section upto which notorsional reinforcementis required

V : Torsional shearstressat a sectionUltimate torsional shearstressat a section

x : Distancein metrebetweenpointsof operationof c~poandapo(x)

X Smallerdimensionof links measuredbetweencentresof legsTensilefibre distancefrom the centroidof the concretesection

Y Side of loadedareaof end block2

V Side of end block2

Largerdimensionof Links measuredbetweencentresof legsA : Deviation of individual test strength from the average test

strengthof ‘n’ teststrengthresultsp : Co-efficient of friction betweencableandduct

Cumulative angle in radian through which the tangent to thecableprofile hasturnedbetweenthepointsof operationof opoand opo(x)

cr : Standarddeviation(population)cpo : Steel stressat the jacking endopo(x): Steel stressat a point, distant ‘x’ from thejacking end

Internal nominaldiameterof sheathing

(v)

IRC: 18-2000

1. INTRODUCTION

TheDesignCriteria for PrestressedConcreteRoadBridges(Post-TensionedConcrete) was first published in December,1965. To cater for the technologicaldevelopmentswhich weretaking placein courseoftime, theCriteriawereexaminedby theTechnicalCommitteesof theIRC andrevisedin 1977and 1985in the light of their recommendations.

In the light of further developmentsin the field ofprestressedconcrete, the task of reviewing the criteria andcarrying out requiredrevisionswas entrustedto the Committeefor Reinforced, Prestressedand Composite Concrete (B-6)consistingof the following personnel

Ninan Koshi .. (‘onvenorA.N. Dhodapkar .. Member-Secretary

MEMBERS

N.K. Sinha JoseKurienS.G. Joglekar PY.ManjureDr. TN. SubbaRao AS. PrasadaRaoM.K. Mukherjee R.A. ChaudharyDr. M.G, Tamhankar G.R. HaridasShitalaSharan D.D. SharmaMaheshTandon Director & Head,Civil Engg.S.A. Reddi Bureauof Indian StandardAshok K. Basa (Vinod Kumar)

1. Viswanathan

EX-OFFLCIO MEMBERS

President,IRC(K.B. Rajoria)

DG(RD)(Prafulla Kurnar)

Secretary,IRC(S.C. Sharma)

CORRESPONDING MEMBER

P.S. Tyagi

IRC: 18-2000

The amendmentsas finalised by this Committee wereconsideredand approved by the Bridge Specifications andStandardsCommitteein theirmeetingheld atNew Delhi on 7thDecember,1999 andlaterapprovedby theExecutiveCommitteein their meetingheld at New Delhi on 14th December,1999.The draft amendmentswere discussedand approvedby theCouncil of the Indian Roads Congressat the 157th CouncilMeeting held at Madurai on 4th January,2000.

It was also decidedthat thedocumentwould bepublishedasa fully revisedCriteriaafterincorporatingall theamendments.

The object of issuing this publication is to establish acommonprocedurefor thedesignandconstructionofPrestressedConcreteRoad Bridges in India. The publication is meant toserve as a guide to both the design engineers and theconstruction engineersbut compliance with the provisionsthereindoesnot relievethemin any wayof theresponsibilityforthe stability, soundnessand safetyofthe structuresdesignedanderectedby them.

The design and constructionof road bridges require anextensive and thorough knowledgeof scienceand techniqueinvolved and should be entrustedonly to specially qualifiedengineers with adequateexperienceof bridge engineering,capableof ensuringcareful executionof work.

2. SCOPE

TheseCriteria cover the design aspectsfor prestressedconcrete(post-tensioned)road bridges (determinatestructuresonly). Thesearenot applicableto thedesignof memberswhichare subjectedto direct compressionlike piers.

2

IRC: 18-2000

3. MATERIALS

3.1. Cement

Any of the following shall be usedwith prior approvalofthe competentauthority

(a) Ordinary PortlandCementconformingto IS: 269

(b) High Strength’PortlandCementconformingto IS: 8112

(c) ordinary PortlandCementconforming to IS:l2269 (Grade53)

(d) SulphateResistantPortlandCementconformingto IS:12330.

3.2. Aggregates

All coarseandfine aggregatesshallconformto IS:383 andtestsfor conformity shall be carriedout asper IS:2386Parts Ito VIII.

3.2.1. Coarseaggregate

3.2.1.1. Coarse aggregateshall consist of clean, hard,strong, densenon-porousand durablepiecesof crushedstone,crushedgravel,naturalgravelor a suitablecombination thereofor other approvedinert material. It shall not contain piecesofdisintegratedstones,soft, flaky elongatedparticles,salt, alkali,vegetablematteror otherdeleteriousmaterialsin suchquantitiesas to reducethe strength or durability of the concrete,or toattack the embeddedsteel.

The nominal maximumsizeofaggregatesshallusuallyberestricted to 10 mm less than the minimum clear distancebetween individual cables or individual untensionedsteelreinforcementor 10 mm less than the minimum cover tountensionedsteelreinforcement,whicheveris smaller.A nominalsize of 20 mm coarseaggregatesshall generallybe consideredsatisfactoryfor prestressedconcretework.

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IRC: 18-2000

3.2.2. Fine aggregates: Fine aggregatesshall conformto Clause302.3.3 of IRC:21.

3.3. Water

Water usedfor mixing and curing shall be in conformitywith Clause302.4 of IRC:21.

3.4. Admixtures may be used in conformity withClause302.2 of IRC:21.

3.5. Steel

3.5.1. The prestressingsteel shall be any of thefollowing:

(a) Plain harddrawnsteel wire conformingto IS: 1785 (Part I) andIS: 1785 (Part II)

(b) Cold drawn indentedwire conformingto IS:6003

(c) High tensile steel bar conformingto IS:2090

(d) Uncoatedstressrelievedstrandconformingto IS:6006,and

(e) Uncoated stress relieved low relaxation steel conforming toIS: 14268,

Data in respectof modulusof elasticity, relaxationlossat1000hrs.,minimumultimatetensilestrength,stress-straincurveetc. shall necessarilybeobtainedfrom manufacturers.Prestressingsteel shallbe subjectedto acceptancetestsprior to actualuseontheworks (guidancemaybe takenfrom BS:4447).The modulusof elasticity value,asper acceptancetests,shallconform to thedesign valuewhich shall be within a rangenot more than 5 percentbetweenthe maximumand minimum.

3.5.2. Untensioned steel : Reinforcement used asuntensionedsteel shall be any of the following

(a) Mild steelandmediumtensile steelbars conformingto IS:432(Part I)

4

IRC: 18-2000

(b) High strengthdeformedsteel barsconforming to IS:1786 and

(c) Hard drawn steel wire fabric conformingto IS: 1566.

The reinforcementbarsbentand fixed in positionshallbefree from rust or scales, chloride contamination and othercorrosion products. Where cleaning of corroded portions isrequired,effective method of cleaning such as sandblastingshall be adopted.

3.5.3. Prestressingaccessorieslike jacks, anchorage,wedges,block plates,etc.beingpatenteditemsshallbeobtainedfrom authorisedmanufacturersonly. Theprestressingcomponentsand accessoriesshall be subjectedto an acceptancetestprior totheir actual use on the works (guidancemay be taken fromBS:4447).

3.6. Sheathing Ducts

The sheathingductsshall beeither in mild steelasper thesub-clause3.6.1 or in HDPE as per sub-clause3.6.2.They shallbe in aslong lengthsaspracticalfrom handlingandtransportationconsiderationswithout gettingdamaged.They shall conform tothe requirements specified in Appendix-L4/IB and a testcertificate shall be furnished by the manufacturer.The testsspecified in Appendix-lB are to be performed as part ofadditional acceptancetests for prestressingsystemsemployingcorrugatedHDPE sheathingductsand arenotmeantfor routinesite testing purposes.

3.6.1. MS sheathing ducts

3.6.1.1. Unlessotherwisespecified,the materialshah beCold Rolled Cold Annealed(CRCA) Mild Steel intended formechanicaltreatmentand surfacerefining but not for quenchhardeningor tempering.

5

1RC: 18-2000

3.6.1.2. Thematerialshallbe cleanandfreefrom rust andnormally of bright metal finish, However, in caseof use inaggressiveenvironmentgalvanisedor lead coated mild steelstrips shall be adopted.

3.6.1.3. Thethicknessofmetal sheathingshallnot be lessthan 0.3 mm, 0.4 mm and 0.5 mm for sheathingducts havinginternal diameterupto 50 mm, 75 mm and 90 mm respectively.For bigger diameterof ducts, thicknessof sheathingshall bebasedon recommendationsof prestressingsystemsupplier.

3.6.1.4. The sheathingshallconform to the requirementsspecifiedin Appendix-lAanda testcertificateshallbe furnishedby the manufacturer.

3.6.1.5. The joints of all sheathingshall be water tightand conform to the provisionscontainedin Appendix-2.

3.6.2. Corrugated HDPE sheathing ducts

3.6.2.1. Unlessotherwisespecified, the material for theductsshall be high-densitypolyethylenewith more than 2 percentcarbonblack to provideresistanceto ultravioletdegradationand shall have the following properties

SpecificDensity : 0.954 g/crn3 at 23°CYield Stress : 18.0 N/mm2TensileStrength 21.0 N/mm2ShoreHardnessD-3 see. value 60

-15 sec. value 58Notch impact strengthat 23°C 10 id/rn2

-40°C 4 kJ/m2Coefficientof ThermalExpansion for 20°C- 80°C : 1.50 x 10~id/rn2

3.6.2.2. Thethicknessof the wall shall be 2.3 ±0.3 mmas manufacturedand 1.5 mm afterloss in the compressiontest,for ductsizeupto 160 mm OD.

6

IRC: 18-2000

3.6.2.3. The ductsshall be corrugatedon bothsides.Theductsshall transmit full tendonstrengthfrom the tendonto thesurroundingconcreteover a length not greaterthan 40 ductdiameters.

3.6.2.4. Theseducts shallbe joined by adopting any oneor more of the following methods,as convenientto suit theindividual requirementsofthe location,subjectto thesatisfactorypressuretests,beforeadoption.

* Screwedtogetherwith maleand femalethreads.

* Joiningwith thick walled HDPE shrinkcouplerswith glue. This

can also be used for connectionwith trumpet,etc.

* Welding with electrofusioncouplers.

Thejoints shallbe ableto withstandan internal pressureof 0,5bar for 5 minutes asper testproceduregiven in Appendix-lA.

4. CONCRETh

Concrete shall be in accordancewith Clause 302.6 ofIRC:21.

S. LOADS AND FORCES

5.1. The loads and forces and load combinationsasperIRC:6-1966 and as applicablefor the given structureshall beduly accountedfor.

5.2. All critical loading stagesshall be investigated.Thestagesstatedbelow may normally be investigated:

(i) Stageprestressing;

(ii) Construction stages including temporary loading, transport,handlinganderectionor any occasionalloads that may occurduring launchingof girders, etc. including impact, if any;

7

IRC: 18-2000

(iii) The design loads as per load combination of 5.1 aboveincluding the following discretestages:

(a) ServiceDead Load+Prestresswith full losses.

(b) ServiceDead Load+Live L,oad+Prestresswith full losses.

(iv) For the combination of loads with differential temperaturegradient effects, maximum 50 per cent live load shall beconsideredand any tensile stressesshall be taken care of by

~roviding adequatelydesigneduntensionedsteel subject to thecrack width limitations stipulated in IRC:21. This shall applynotwithstanding the provision contained in Clause 7.2.2.However, in the ease of precastsegmentalconstruction notensionshall be permittedunderthis load combination.

(v) Ultimate load, as perClause 12.

6. STAGE PRESTRESSING

Stageprestressingis permissible.Thenumberof stagesofprestressingand grouting shall be reducedto the minimum,preferably not more than 2. However, concrete shall haveattained a strength of not less than 20 MPa before anyprestressingis applied.

7. PERMISSIBLE STRESSES IN CONCRETE

7.1. Permissible Temporary Stressesin Concrete

7.1 . I. Thesestressesarecalculatedafteraccountingforall losses except those due to relaxation of steel, residualshrinkageand creepof concrete.

7.1.2. The compressivestressproduceddue to loadingmentionedin Clause5.2 (ii) shall not exceed0.5 fç, which shallnot be more than 20 MPa, where is the concretestrengthatthat time subjectto a maximumvalue ofJk~

8

IRC: 18-2000

7.1.3. At full transferthecubestrengthof concreteshallnot be less than 0.8 f~k’Temporarycompressivestressin theextremefibre ofconcrete(includingstageprestressing)shallnotexceed0.50J~,subjectto a maximumof 20 MPa.

7.1.4. The temporary tensile stressesin the extremefibres of concreteshall not exceed1/10th of the permissibletemporarycompressivestressin the concrete.

7.2, PermissibleStress in Concrete during Service

7.2.1. The compressivestressin concreteunderserviceloads shall not exceed0.33 1k’

7.2.2. No tensile stress shall be permitted in theconcreteduring service.

7.2.3. If pre-cast segmentalelements are joined byprestressing,thestressesin theextremefibres of concreteduringservice shall always be compressiveand the minimumcompressivestressin an extremefibre shallnot be lessthan fivepercentof maximumpermanentcompressivestressthatmay bedeveloped in the same section. This provision shall not,however,apply to crossprestresseddeck slabs.

7.2.4. The structureshall also be checkedfor 20 percent higher time dependent losses like creep, shrinkage,relaxation,etc. Under this condition, no tensilestressshall bepermitted.

7.3. Permissible Bearing Stress Behind Anchorages

The maximum allowable stress,immediately behind theanchoragesin adequatelyreinforcedendblocksmaybe calculated

9

11W 18-2000

by the equation

= 048 f or 0.8 whichever is smaller

Where 1h = the permissiblecompressivecontactstressin concreteincluding any prevailing stress as in the case ofintermediateanchorages

A, = thebearingareaof theanchorageconvertedin shapetoa squareof equivalentarea

A, = the maximumareaof the squarethatcan be containedwithin the member without overlapping thecorresponding area of adjacent anchorages,andconcentricwith the bearingareaA,.

Notes (i) The abovevalueof bearingstressis permissibleonlyif thereis a projectionof concreteof at least50 mm orb¼,whicheveris moreall roundthe anchorage,where

is as shown in Fig. 1.

AMA

Fig. 1.

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IRC: 18-2000

(ii) Where embedded anchorages are provided, thereinforcement details, concrete strength, cover andother dimensions shall conform to the manufacturer’sspecifications/specialistliterature.

(iii) Thepressureoperatingon the anchorageshall be takenbefore allowing for losses due to creep and shrinkageof concrete and relaxation of steel, but after allowingfor losses due to elastic shortening,relaxationof steeland seatingof anchorage.

8. PERMISSIBLE STRESSESIN PRESTRESSINGSTEEL

Maximum jack pressureshall not exceed90 per cent of0.1%proof stress. For the purposeof this Clause0.1%proofstressshall be taken as equal to 85% of minimum UltimateTensileStrength(UTS).

9. SECTION PROPERTIES

9.1. For membersconsistingof precastaswell ascast-in-situ units, due considerationshall be given to the differentmoduli of elasticity of concrete in the precastand in-situportions.

9.2. Openings In Concrete Section

For the purposeof determiningthe flexural stressesbothprior to and after grouting of the cables or tendons, thepropertiesof the sectionsuch as area,positionof centroidandmoment of inertia may be basedupon the full sectionof theconcretewithoutdeductingfor theareaof longitudinalopeningsleft in the concretefor prestressingtendons,cable ducts orsheaths.No allOwanceforthe transformedareaoftheprestressingtendonsshall, however,be made.

Deduction shall be made for the holes of transverseprestressingtendonsat sectionswheretheyoccur,for determiningthe stressesbeforegrouting of theseholes.

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IRC: 18-2000

9.3. Minimum Dimensions

9.3.1. ‘T’ beams

9.3.1.1. The thicknessof the web shall not be less than200 mm plus diameterof duct hole. Wherecablescrosswithinthe web, suitableincreasein the thicknessover the abovevalue

shall be made.

9.3.1.2. The effectivewidth of the flangeof a ‘T’ beamshall conform to Clause305.15.2of IRC:21.

9.3.1.3. Theminimumthicknessofthedeckslabincludingthat at cantilever tips shall be 200 mm.

9.3.1.4. In caseof multi-beamarrangement,at leasttwocross girders, one at eachsupport,shall beprovided.Forbridgeshaving beam and slab type of superstructure,the numberoflongitudinalbeamsshallnotbe lessthan3 exceptfor singlelaneand pedestrianbridges.The depthof the end crossgirders shallbe suitably adjustedto allow accessfor proper inspection ofbearingsand to facilitate positioningofjacks for future liftingup ofthesuper-structure.Thethicknessof crossgirdersshallnotbe lessthan theminimumwebthicknessoflongitudinalgirders.

9.3.1.5. In caseofcompositeconstructionwith prestressedconcretegirdersand RCC deckslab,the soffit ofdeckslab shallbe in line with the top of the flange of the girders.

9.3.2. Box girders

9,3.2.1. The thicknessof the web shall not be less thand136 plus twice the clear cover to the reinforcementplusdiameterof the duct hole where ~d’is the overall depth of thebox girdermeasuredfrom thetop ofthedeckslabto thebottomof the soffit or 200 mm plus the diameter of duct holes,

12

IRC: 18-2000

whichever is greater. Where cables cross within the web,suitableincreasein the thicknessover the aboveshall bemade.

in case of cast in situ cantilever construction, if theprestressingcablesareanchoredin the web, the web shall belocally thickenedto not less than 350 mm nor less than thatrecommended by the prestressingsystem manufacturer, subjectto designrequirements.

9.3.2.2. The thicknessof thebottom flangeof box girdershall be not less than 1/20th of the clear web spacingat thejunction with bottom flangeor200 mm whicheveris more. Fortop flange minimum thicknessshall be asper Clause9.3.1.3.

9.3.2.3. For top and bottom flange having prestressingcables,the thicknessof suchflange shall not be less than 150mm plus diameterof duct hole.

9.3.2.4. In box girders, effective and adequatebond andshear resistance shall be providedat thejunction of thewebandtheslabs.The slabsmaybe consideredasan integral partof thegirder and the entire width may be assumedto be effective incompression.

For very shortspansorwhereweb spacingis excessiveorwhereoverhangsareexcessive,analyticalinvestigationshall bemadeto determinethe effective flangewidth.

9.3.2.5. For cantilever construction,preferenceshall begiven to box type crosssection with diaphragmsprovided atsupports.Suddenchangein depthof superstructureshouldnotbepermitted.Forreducingthethermaleffect suitableventilationshould be provided in box sections.

9.3.2.6. Haunchesof minimumsizeof300mm(horizontal)and 150 mm (vertical) shall be provided at the four extreme

13

IRC: 18-2000

inner cornersof thebox section.For all othercornersfillets ofsuitable sizemay be provided.

9.3.2.7. The minimum clear height inside the box girdersshall be 1.5 m to facilitate inspection.

9.4. Diaphragms/CrossGirders

Diaphragms shall be provided dependingupon designrequirements.Thethicknessof diaphragmsshallnot be lessthanthe minimum web thickness.

10. MODULI OF ELASTICITY

10.1. Modulus of Elasticity of Steel (E)

10.1.1. For the purposeof designthe following nominalvaluesof modulusof elasticity canbeassumedexceptwherethemanufacturerscertified valuesor test resultsare available:

Table I

Type of steel Modulus of elasticityMPa

Plain hard-drawnwires (conformingto IS:1785and IS:6003) 2.1 x 10~

High tensile steel barsrolled orheattreated(conformingto IS:2090) 2.0 x 10~

Strands(conformingto IS:6006) 1.95 x 10~

10.1.2. Representativevaluesof modulusof elasticity assuppliedby the manufacturersor asper testresultsbasedon onetestof 3 samplesfor every lot of 10 tonnes or part thereofshallbe usedfor verification of the elongationcalculations.

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IRC: 18-2000

10.2. Modulus of Elasticity of Concrete (E)

Unless otherwise determinedby tests, the modulus ofelasticity, E of concreteshall be assumedto havea value

E = 5700 ~ MPa

The valueof the modulus of elastcity E oftheconcreteatcj

j daysmay be taken to be.

E. = 5700 ~ MPa

11. LOSSES IN PRESTRESS

Decreasein prestressin steel due to elastic shortening,creepand shrinkageofconcrete,relaxationof steel,friction andseatingof anchoragesshall be calculatedon thefollowing basis:

11.1. Elastic Shortening

The loss due to elastic shorteningof concreteshall becomputedbasedon the sequenceof tensioning.However, fordesign purposes,the resultant loss of prestressin tendonstensionedone by onemay becalculatedon thebasisofhalf theproductof modularratio and the stressin concreteadjacenttothetendonsaveragedalong the length. Alternatively the lossofprestressmay be computed exactly based on sequenceofstressing.

11.2. Creep of Concrete

The strain due to creep of concreteshall be taken asspecified in Table 2.

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IRC: 18-2000

Table 2

Maturity of concreteat theof stressingas a percentage

time Creep strainof

per 10 MPa

40 9.4 x l0-~50 8.3 x l0~60 7.2 x l0~~70 6.1 x l0-~75 5.6 x 1Q~~80 5.1 x I0~90 4.4 x 10~.100 4.0 x l0~110 3.6 x l0’~

Notes: (i) The creepstrainduring anyinterval may be takenasthe straindueto a sustainedstressequal to the arithmetic meanof theinitial andthe final stressoccurring during that interval.

(ii) The stressfor the calculationof the loss dueto creepshall betakenasthestressin concreteatthecentroidof theprestressingsteel, Variation in stress, if any, along the centroid of theprestressingsteel,may be accountedfor.

(iii) Valuesof creepstrain for intermediatefigures for thematurityof concreteat the time of stressingmay be interpolatedtakinga linear variation betweenthe valuesgiven above.

(iv) The above valuesare for Ordinary Portland Cement.

11.3. Shrinkage of Concrete

The loss in prestressin steel,due to shrinkageofconcreteshall be estimatedfrom the values of strain due to residualshrinkagegiven in Table 3.

11.4. Relaxationof Steel

Relaxationof steelshall invariablybe verified by testingtoascertainconformanceto the respectivecodesfor prestressing

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IRC: 18-2000

Table 3

Age of concreteattheof stressing,in days

time Straindueto residualshrinkage

3 4.3x1047 3.5x10410 3.0 x l0~14 . 2.5 x 10’~21 2.0 x l0~28 1.9 x 10’~90 1.5 x l0~

Notes: (i) Valuesfor intermediatefigures for any ageof concretemay beinterpolatedtaking a linear variation betweenthe values given.

(ii) The above are for OrdinaryPortlandCement.

steel as per Clause 3.5.1. For calculation of permissibletemporarystress in concrete as per Clause 7.1 lossesdue torelaxation of steel shall be taken on the basis of 1000 hourvalue. For calculationof stressin service condition, long termrelaxationlossvalues occurringat about0.5x106hoursshall beconsidered,whichshallbe takenas3 times the 1000hour valuegiven in Table4A.

Table 4ARelaxation loss at 1000 hours at 20°C±2°C(as %of initial stress)

Initial stress Relaxation loss forNormal relaxation

steel (%)

Relfor lo

s

a.xation lossw relaxationtee! (%)

0.5 fp 0 00.6 fp 2.5 1.250.7 fp 5.0 2.50.8 fp 9.0 4.5

Notes: (i) For intermediatevalues linear interpolationmay be done(ii) fp Minimum Ultimate Tensile Stress (UTS) of steel

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IRC: 18-2000

Table 4BRelaxation betweenrelaxationlossand time upto 1000

Time in Hours 1 5 20 100 200

Relaxation loss 15 25 35 55 65 85 100as % of loss at1000 hrs

11.5. LossesDue to Seating of Anchorages

Dependingupon the type of post tensioning, lossesinprestressoccur due to slip of wires, draw-in of male cones,strains in anchorage,the valueof which shall be asper testsormanufacturer’s recommendations and duly accounted, for

consideringreversefriction nearthe anchorageends.For thispurposethe values of co-efficient of friction and wobble co-efficient shall be taken sameas those stipulated for positivefriction.

11.6. FrictIon Losses

Steel stressin prestressingtendonso~,(x) at any distancex from thejacking end canbe calculatedfrom the formula

ci = o’ (x) (p0 + kr)

the steel stress at the jacking endthe base of NaperianLogarithmsthe co-efficient of frictionthe cumulativeangle in radiansthrough which thetangentto the cable profile has turnedbetweenthepointsof operationof ci and ci (x).the steel stress at a point, distant ‘x’ from thejackingend

k = the wobble co-efficientper metre lengthof steelx = the distancebetween pointsof operation of o,0 and

cr,, (x) in metres.

hours500 1000

Where ci =

e

/1 =

0=

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IRC: 18-2000

Thevalueofp andk given in Table 5 may beadoptedforcalculatingthe friction losses.

Table 5

Type of hightensile steel

Type of duct orsheath

Valuesrecommin design

ended to be used

k per metre p

Wire cables Bright metalGalvanizedLead coatedUnlined duct inconcrete

0.00910,00460,00460.0046

0.250.20.180.45

Uncoatedstress Bright metal 0.0046 0.25relieved strands Galvanized

LeadcoatedUnlined duct inconcreteCorrugatedHDPE

0.00300.00300.0046

0,0020

0.200.180.50

0.17

Notes: (i) Values to be used in design may be altered to the valuesobserved,on satisfactoryevidencein support of suchvalues.

(ii) For multi-layerwire cableswith spacerplatesproviding lateralseparation,thevalueofp maybe adoptedon the basisof actualtest results.

(iii) Whenthe direction of friction is reversed, the index of ‘e’ in theaboveformula shall be negative.

(iv) Theaboveformulais of generalapplicationandcanbe usedforestimationof friction betweenanytwo pointsalong thetendondistant ‘x’ from eachother.

Thevaluesofp andk usedin designshallbe indicatedonthe drawings for guidancein selectionof the material andthemethods that will produce results approaching the assumedvalues.

11.7. For structures constructed by segmentalconstruction or other complex construction methods which

19

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IRC: 18-2000

require accuratedeterminationanddetailedinformation of timedependenteffects, specialistliteraturemay be referred to.

12. ULTIMATE STRENGTH

A prestressedconcretestructureandits constituentmembersshallbe checkedfor failure conditjonsat an ultimateloadof 1 .25G + 2 SG + 2.5 Q undermoderateconditionand 1.5 G + 2 SG+ 2.5 Q under severeexposureconditionswhere G, SO andQdenotepermanentload, superimposeddeadload and live loadincluding impactrespectively.The superimposeddeadloadshallincludedeadloadof precastfootpath,handrails, wearingcourse,utility services,kerbs etc. For sections,where the dead loadcauseseffects oppositeto those of live load, the sectionsshallalsobe checkedfor adequacyfor a load of 0 + SO + 2.5 Q.

13. CALCULATION OF ULTIMATE STRENGTH

Under ultimate load conditions, the failure may eitheroccurby yielding of the steel(under-reinforcedsection)or bydirect crushingof the concrete(over-reinforcedsection).Ultimatemomentof resistanceof sections,under thesetwo alternativeconditions of failure shall be calculated by the followingformulaeandthe smallerof the two valuesshallbe takenas theultimate momentof resistancefor design

(i) Failure by yield of steel(under-reinforcedsection)M =O.9dAfu/i b , p

Where A = the area of high tensile steelf = the ultimate tensile strength for steel without definite

yield point or yield stress or stress at 4 per centelongation whichever is higher for steel with adefinite yield point.

= the depth of the beam from the maximumcompressionedgeto thecentreof gravity of the steeltendons.

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IRC: 18-2000

Non-prestressedreinforcement may be considered ascontributing to the available tension for calculation of theultimate momentof resistancein an amount equal to its areatimes its yield stress,providedsuchreinforcementis weldedorhassufficient bondunderconditions of ultimate load.

(ii) Failureby crushingof concrete

M,,~,=0.176 bd j~.

for a rectangularsection

= 0.176 bd: ~k + 0.8 (B~b)~db- x

for a Teebeam

Where b = the width of rectangularsectionor web of a Teebeam

B1 = the width of flange of Tee beam= the thicknessof flangeof a Tee beam

14. SHEAR AND TORSION

14.1. Shear

14. 1.1. The calculationsfor shearare only requiredforthe Ultimate Load.

At any sectiontheultimateshearresistanceof theconcretealone,V shallbeconsideredfor thesectionbothuncracked(seeClause 14.1.2) and cracked (see Clause 14.1.3) in flexureirrespectiveof the magnitudeof M, and the lesservaluetakenand, if necessary,shear reinforcement (see Clause 14.1.4)provided.

For a crackedsection,the conditionsof maximum shearwith co-existentbendingmomentandmaximumbendingmomentwith co-existentshearshall both be considered.

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IRC: 18-2000

Theeffect of the vertical componentof thebottom flangeforce in membersof variable depth may also be consideredwhere applicable.While calculatingthis componentthe designmoment to be considered shall be concomitantwith the designshear force being considered.

14.1.2. Sectionsuncrackedin flexure

14.1.2.1. The ultimate shear resistance of a sectionuncrackedin flexure, V~,correspondsto the occurrenceof amaximum principal tensile stress,at the centroidalaxis of thesection,of£ = 0.24

In the calculation of J~,the value of prestressat thecentroidal axis hasbeen taken as 0.8 f. The value of V~ isgiven by

= 0.67 bd JXco.s%t;

Where *b = width in the caseof rectangularmemberandwidth

of the rib in the caseof T, I and L beamsd = overall depthof the member

= maximum principal tensile stress given by 024 ,f7~4 = compressivestressatcentroidalaxisdueto prestress

taken aspositive.

*where the position of a duct coincideswith the position of maximum

principal tensile stress,e.g., at or nearthejunction of flange andweb neara support, the value of b should be reduced by the full diameter of the ductif ungroutedandby two-thirds of the diameterif grouted.

In flangedmemberswherethecentroidalaxis occursin theflange, the principal tensilestressshould be limited to 0.24J7at the intersectionofthe flangeandweb; in this calculation,0.8of the stressdue to prestressat this intersectionmaybe usedincalculating V~0.

For a section uncracked in flexure and with inclined

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IRC: 18-2000

tendons or vertical prestress,the componentof prestressingforce normal to the longitudinal axis of the membermay beaddedto V

Co

14. 1.2.2. For bridge deckswith precastprestressedbeamsand cast-in-situdeck slab, V~,canbeevaluatedasgiven below:

M = ultimatedesignmoment acting on the precast section alone= ultimate design shearforce acting on the precast section

aloneIp = secondmomentof areaof precastsection alone

= second moment of area of composite section(Ay)~= first moment of area above composite centroid for precast

section alone(Av) = first moment of area above compositecentroidfor composite

section

f = stressat compositecentroiddue to M

= stressat compositecentroid due to prestress4 =

= stressat compositecentroid due to

V1 (Ay)

= (Ib) ~, if f > J then section revision is required

~~c2 = additionalultimate shearforcewhich can be carriedby thecomposite section before the principal tensile stress atcompositecentroidreachesf, = 0.24 (fck)w

(I b)= (Ay)c~’

t+4f~)”2-.1)Vco = V±V

14.1.3. Sectionscrackedin flexure : The ultimate shearresistanceof a section cracked in flexure, Vcr may be calculatedusing the equationgiven below

Vcr = 0.037bd., V

Where db = is the distancefrom the extreme compression fibre

23

1RC: 18-2000

to the centroid of the tendons at the sectionconsidered;

= is thecrackingmomentat the sectionconsidered,Mt

= (0.37 ,J17 + 0.8 f~~IIyin which is the stress

due to prestressonly at the tensile fibre distanceyfrom the centroidof the concretesectionwhich hasa secondmomentof areaI;

V andM = are the shear force and corresponding bendingmomentat the sectionconsidereddue to ultimateloads;

V = shouldbe taken as not less than 0.1 bd ~ The

value of V~calculated at a par~cular sectionmay beassumed to be constant for a distance equal to db/2,measuredin the direction of increasing momentfrom that particularsection.

Fora sectioncrackedin flexureandwith inclinedtendons,the componentof prestressingforcesnormal to the longitudinalaxis of the membershould be ignored.

14.1.4. Shear reinforcement : When V, the shearforcedue to the ultimate load is less than ~~/2 then no shearreinforcementneedbeprovided.A minimumshearreinforcementshall be providedwhen Vis greaterthanV~/2in theform of linkssuch that

A O.87F= 0,4MPa ‘1)

S~, b

When the shearforce V, due to the ultimate loads exceedsV~,the shearreinThrcementprovided shall be such that

A,, V—V.

S0.S7frrd, (2)

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IRC: 18-2000

Where V = is the shearforce that can be carriedby the concrete= is theyield strengthof the links/shearreinforcement

or 0.2 per cent proof stress which should be taken asnot greaterthan 415 MPa

A = is the corss-sectional area of the two legs of a linkS = is the link spacing along the length of memberd1 = is the depth from the extreme compression fibre

either to the longitudinal bars having diameter notless than the link bar over which the link will passor to the centroid of the tendons, whichever isgreater.

In beams, at both cornersin the tensilezone, a link shallpassround a longitudinal bar, a tendonor a group of tendonshaving a diameternot less than the link diameter.A link shallextendas close to thetensionandcompressionfacesaspossible,with dueregardto cover.The links providedat a crosssectionshall between them enclose all the tendons and additionalreinforcement provided at the cross section and shall beadequatelyanchored,Fig. 2 (i-ui). In no caseshearreinforcementprovided shall be less than that required as per equation(I)abovewhen V is greaterthan V/2.

14.1.5. Maximum shear force : In no circumstancesshall the shear force ‘V’, due to ultimate loads, exceedtheappropriate value given in Table6 multiplied by bdb, where ~b’is as defined in sub-clause 14,1.2, less either the diameter of the

duct for ungroutedor two-thirds the diameterof the duct forgrouted ducts and ~db’is thedistancefrom thecompressionfaceto theéentroidof theactualsteelareain tensilezonebut not lessthan 0.80 times the overall depthof the member.

The shear force V should include an allowance forprestressingonly for sectionsuncrackedin flexure (see Clause14.1.2).

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IRC: 18-2000

Connector details at junctionof intermediate web andflangesof box girder

(Ii)

Connector details atjunction of end web andflangesof box girder

(iii)

Fig. 2, Connector reinforcement for compressionflange and tensionflange

A COt~N~C1’O~I / A~ ~,O$A$V/$V

Connector details tensionflange (bulb) of T-beam

(I)

- 0P P11 hIlL

- t~u o, ~ STIlL

I, — mcisc Il lU mgi

-

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IRC: 18-2000

Table 6. Maximum Shear Stress

ConcreteGrade

30 35 40 45 50 55 60

MPa MPa MPa MPa MPa MPa MPaMaximum 4,1 4.4 4.7 5.0 5.3 5.5 5.8ShearStress

Note : For intermediatevalues linear interpolationmay be done.

14.2, Torsional Resistanceof Beams

14.2.1. General : Torsion does not usually decide the

dimensionsof members, therefore,torsional designshould becarriedout asa checkafter theflexural design.Tn general,wherethe torsional resistanceor stiffness of membershas not beentaken into account in the analysis of the structureno specific

calculationsfor torsion will be necessary,adequatecontrol ofany torsional crackingbeingprovided by the requirednominalshearreinforcement.Therefore,provisions madein the clauseare to be followed when the effect of torsion is appreciable.Alternative methodsof designingmemberssubjectedto combinedbending, shear and torsion could also be used provided therationality of the method adoptedis justified.

14.2.2. Stressesand reinforcement : Calculations fortorsion are requiredonly for ultimate loads and the torsionalshear stressesshould be calculatedassw’ning a plastic stressdistribution. Where the torsional shear stress V~exceedsthevalue ~.from Table 7, reinforcementshall be provided.In nocase,shall the sum of shearstressesresulting from shearforceand torsion (V +J’~)exceedthe valueof V~from Table 7 nor inthe caseof small sections(V1 < 550 mm) should the torsional

27

IRC: 18-2000

shear stress, V~,exceed V~x Y,,~,where ~‘1 is the largerdimensionof a link.

Torsionreinforcementshallconsistofrectangulareffectivelyclosed links together with longitudinal reinforcement. Thisreinforcementis additionto that requiredfor shearor bending.

Table 7. Ultimate Torsion Shear Stress

ConcreteGrade

30 35 40 45 50 55 60

V~MPa0.37

MPa0.40

MPa0.42

MPa0.42

MPa0.42

MPa0.42

MPa0.42

V,, 4.10 4.45 4.75 5.03 5.30 5.56 5.81

14.2.3. Computation of torsional stressesfor variouscross sections

14.2.3.1.Rectangular section

Where T =

max

= (h2~nm)x[hm.xhn~.n)

is the torsionalmomentdue to ultimate loadsis the smallerdimensionof the sectionis the larger dimensionof the section

Torsional reinforcementshouldbe provided suchthat

A,,, 7’

5,, 0.8X1}~(0.87f,j

ASL �

Where A =

=

is the total areaof legs of closedlinks at a sectionis the areaof longitudinal reinforcement

2T

28

IRC: 18-2000

is the yield strength of longitudinal reinforcementwhich shouldnot be taken greater than 415 MPa

= is the yield strengthof linksS, is the spacingof the links

= is the smaller dimension of the link measuredbetweencentresof legs

Y1 = is the largerdimensionof the link measuredbetween

centresof legs.

To preventa detailing failure the closed links shall bedetailed to have minimum cover and a pitch less than thesmallest of (X1 + Y)/4, 16 times longitudinal corner bardiametersand200 mm. The longitudinal reinforcementshallbepositioneduniformly suchthat thereis a bar at eachcornerofthe links. Thediameterof thecornerbarsshallbenot lessthanthe diameterof the links.

14.2.3.2.T, L and I sections : Such sections shall bedivided into component rectanglesfor purposeof torsionaldesign.This shall be done in sucha way as to maximize thefunction E(h x h

3 ~ where h and h . are the largerandmax in: max nun

smallerdimensionsofeachcomponentrectangle.Eachrectangleshall thenbe consideredsubjectto a torque

T(hmax Xh’mai)

~ (h,,,,,x1I~~~~)

Reinforcementshall be so detailedasto tie the individualrectangles together. Where the torsional shear stress in arectangleis lessthan no torsional reinforcementneedto beprovided in that rectangle.

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IRC: 18-2000

14.2.3.3.Box section

V=T/2h AI a’o a

Where h = is the wall thicknessof memberswherethe stressisdetermined;

A,, = is the areaenclosedby the centreline of membersforming the box.

Torsional reinforcementis to be providedsuch that

A,,, 7’

S ~ A,{0.87J~,,,)

A >A,,,(PerimeierofAo~f~SL’S1~ 2 ) j,

The detailingrequirementsof Clause14.2.3.1,should stillbe observed.In detailing the longitudinal reinforcementto caterfor torsionalstressesaccountmaybe takenof thoseareasof thecross section subjectedto simultaneousflexural compressivestresses and a lesseramountofreinforcementin thecompressivezone may be takenas (Area of section subject to

flexural compression)Reductionin steel area= f X0.87f,,,

Where j,,, = is the average compressivestress in the flexuralcompressivezone,and

f = is theyield stressof longitudinalsteelin compression.

15. MINIMUM REINFORCEMENT

15.1. General

The quantity of untensionedsteel requiredfor designorconstructionalpurposes shall not be less than the minimumstipulatedin Clauses 15.2 to 15.4. Varioustypes of minimumsteel requirementsneed not be addedtogether. Bars in suchreinforcementshall, however, not beplacedmore than 200 mmapart.The minimum diametershall not be less than 10 mm for

30

IRC: 18-2000

severecondition of exposureand 8 mm for moderateconditionof exposure.

In case of in-situ segmental construction for bridgeslocated in marine environment continuity of untensionedreinforcementfrom one segmentto the next shall be ensured.

15.2. In theverticaldirection,aminimumreinforcementshall be provided in the bulb/web of the beams/ribof boxgirders, suchreinforcementbeingnot less than 0.3 percent ofthe crosssectionalareaof the bulb/web in plan for mild steeland0.18 per centfor HYSD barsrespectively.Suchreinforcementshall be asfar aspossibleuniformly spacedalong the length oftheweb. In the bulb portion, the crosssectionalareaof bulb inplan shall be taken.

In all the corners of the section, these reinforcementsshould passrounda longitudinal barhavinga diameternot lessthanthat~of thevertical baror rounda groupof tendons.Fortee-beams,thearrangementin thebulbportion shall beasshowninFig. 2.

15.3. Longitudinal reinforcementsprovided shall notbe less than 0.25 per centand 0.15 per centof the gross crosssectionalarea of the section for mild steel and HYSD barsrespectively,wherethe specifiedgradeof concreteis less thanM 45. In casethe grade of concreteis M 45 or more, theprovision shall be increasedto 0.3 per centand 0.18 per centrespectively. Such reinforcementshall as far as possible beevenly spacedon the periphery.Non-prestressedhigh tensilereinforcementcan also be reckonedfor thepurposeof fulfillingthe requirementof this clause.

15.4. For solid slabsand top and bottom slabsof boxgirders,thetop andundersideoftheslabsshall beprovidedwith

31

IRC: 18-2000

reinforcementconsistingof agrid formedby layersof bars.Theminimum steelprovided shall be asfollows

(i) For solid slabs and top slab of box girders: 0.3 percentand0.18percentofthegrosscrosssectionalareaoftheslab for MSandHYSD barsrespectively,which shallbe equallydistributedat top and bottom.

(ii) For soffit slab of box girders: The longitudinal steelshall beat least 0.18 per cent and 0.3 per cent of sectionalarea forHYSDand MS bars respectively. The minimum transversereinforcementshall be 0.3 per cent and 0,5 per cent of thesectional area for FIYSD and MS bars respectively. Theminimum reinforcementshall be equallydistributed at top andbottom,

15.5. For cantileverslab minimum reinforcementof 4nos. of 16 mm dia HYSD barsor 6 nos. of 16 mm dia MS barsshould be provided with minimum spacingat the tip dividedequally betweenthe top and bottom surfaceparallel to support.

N.B. Notwithstandingthenomenclature“untensionedsteel”,thisprovisionof reinforcementmay beutilisedfor withstandingall actionaffects, if necessary.

16. COVER AND SPACING OF PRESTRESSING STEEL

16.1. Whereverprestressingcableis nearestto concretesurface, the minimum clear cover measuredfrom outsideofsheathing,shallbe 75 mm.

16.2. The minimum clear cover to uritensionedreinforcementincluding links andstirrups shallbeasperClause304.3 of IRC:21.

16.3. A minimum clear distanceof 50 mm or diameterof the duct, whicheveris greater,shall be maintainedbetweenindividual cableswhen groupingof cablesis not involved.

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IRC: 18-2000

16.4. Grouped Cables

16.4.1, Groupingof cablesshallbeavoidedto theextentpossible.If unavoidable,only vertical grouping of cables,upto2 cablesmay be permittedas shown in Fig. 3. The minimumclearspacingbetweengroupsshallbe diameterofthe ductor 50mm, whicheveris greater.

Note : In case of severe conditions of exposure,grouping ofcables should bealtogetheravoided.This maybe achievedby the useof high capacitystrands.

/ N00

00

a !~—~~ch’-

a, b 50 mm or diameterof duct whicheveris greater,C 75 mm

Fig. 3.

8 8 II

a

-L

C

-r

b

8 8 T

C

Ta l”-~c I.—

33

IRC: 18-2000

16.4.2. Individual cablesor ductsof groupedcablesshallbe deflectedor drapedin theendportionsofmembers.Theclearspacingbetweencablesor ducts in the end one metre of themembersas specifiedin Clause16.3 shall be maintained.

16.5. Theplacementof cablesor ductsandtheorderofstressingandgrouting shall be so arrangedthat the prestressingsteel,whentensionedandgrouted,doesnot adverselyaffect theadjoining ducts.

16.6. All cablesshallbethreadedby threadingmachineor any contrivanceinto preformedducts. Wherevertwo stageprestressingis contemplated,a dummycoreshallbeprovidedinthe preformedducts of the secondstagecables,which shall bepulled out afterthe first stageprestressingand grouting is over.Thereafter,thecablesfor the secondstageshallbe threadedintothepreformedducts.Whereprestressingin morethantwo stagesis contemplated,the above procedureshall be followed forsubsequentstagecablesalso.

Stressingof cable/partof cable to avoid shrinkagecracksshall not be treatedas a stage.

17. END BLOCKS

17.1. End block shall be designedto distribute theconcentratedprestressingforce at the anchorage. It shall havesufficient areato accommodateanchoragesat the jacking endand shall preferablybe as wide as the narrowestflange of thebeam.Lengthofendblock in no caseshallbe lessthan600 mmnor less thanits width. Theportionhousingtheanchoragesshallasfar as possiblebe precast.

17.2. The burstingforces in the end blocks, should beassessedon the basis of the ultimate tensile strength. The

burstingtensile force,~ existing in an individual squareend

34

IRC: 18-2000

block loaded by a symmetricallyplaced squareanchorageorbearingplate, may be derivedfrom Table 8.

Where 2 Y = is the side of endblock2 Y = is the side of loadedarea

= is the load in the tendon assessedas above

= is the burstingtensile force.

Table 8. DesignBursting Tensile Forces In End Blocks

Y /Y 0.3 0.4 0.5 0.6 0.7~0 ~

F~7Ph 0.23 0.20 0.17 0.14 0.11

Notes (i) For intermediatevalueslinear interpolation may be made.(ii) The values in the tableabovegenerallyhold good for internal

anchorages.For external anchoragesthe design force may beincreasedby 10 per cent.

This force, F~will be distributed in a regionextendingfrom 0.2 y to 2 Y from the loaded faceof the end block asshownin Fig. 4.

—‘l 1i~O2Yo _____~ 2Yo ‘1

Fig. 4.

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IRC: 18-2000

Reinforcementprovided in this region to sustain thebursting tensile force may be calculatedbased on a tensilestrengthof 0.87j exceptthat the stressshould be limited to avaluecorrespondfngto a strainof 0.001 whenthe concretecoverto the reinforcementis less than 50 mm.

In therectangularendblocks, theburstingtensileforces inthe two principal directions should be assessedon the similarbasisas in Table 8.

When circular anchoragesor bearingplatesareused,theside of the equivalentsquareareashould be derived.

Wheregroupsof anchoragesor bearingplates occur, theend block should be divided into a series of symmetricallyloadedprisms and eachprism treatedin the abovemanner.Indetailing the reinforcementfor the end block as a whole, it isnecessaryto ensure that the groups of anchoragesareappropriatelytied together.Special attention should be paid toendblockshavinga crosssectiondifferent in shapefrom thatofthe generalcrosssectionof the beamand referenceshouldbemade to specialist literature. Compliance with the aboverequirementswill generallyensurethat bursting tensile forcesalong the loadedaxis are provided for. In casewhere largeconcentratedtendonforcesare involved altemativemethodsofdesign basedon specialist literature and manufacturer’sdatamay be moreappropriate.

17.3. Considerationshouldalsobegivento thespallingtensilestressesthat occurin endblocks. Wheretheanchorageorbearing plates are highly eccentric, these stressesreach amaximum at the loadedface. The end faceof anchoragezoneshall be continuously reinforced to prevent edge spalling.

36

IRC: 18-2000

Reinforcementshall be placed as close to the end face aspossible.

18. THICKENING OF WEBS OF GIRDERS

The thickeningof websof girders towardsthe endblocksshall be achievedgraduallywith a splay in plan of not steeperthan I in 6. Suitable thickening for isolatedanchoragesawayfrom theendblocksshallbemadewhenevernecessaryto reducestressconcentration.

19. ANCHORAGE OF CABLES AND STRESSING

Anchorageof cablesin the top deck surfaceshall not bepermitted. All anchoragesshall be properly sealed afterprestressing and grouting operations.All wires/strandsin onecableshouldbe stressedsimultaneouslyby usingmulti-stressingjack.

20. SPLAY OF CABLES IN PLAN AND MINIMUM RADIUSOF CABLES IN ELEVATION

The splay of cablesin plan, for bringing them from theirposition in thebottom flangeat mid-spaninto the web towardsthe supports shall not bemore than I in 6. Thepoints of splayshall be suitably staggeredon both sides of the longitudinalcentre line of the web of the girder. The minimum radius ofcurvature,spacingandcoverfor curvedcablesshallbespecifiedto ensurethat bursting of the sidecoverboth perpendiculartotheplaneof curvatureandin theplaneof curvatureof theductsdoesnot takeplace. Guidancein this regardmay be takenfromBS:5400: Part 4: (Appendix-D) subject to spacingand coverstipulationsgiven in Clause 16.

37

IRC: 18-2000

21. SLENDER BEAMS

Slenderbeamsare thosein which

(a) ratio of span to width of top flange is more than 60, and

(b) ratio of width of top flange to the depthof beamis less than

1/4.

For such beams permissible stress shall be reducedsuitablyandtheyshallalsobe providedwith adequatetemporaryrestraints during handling and erection which should beinvestigated.

22. EMERGENCY CABLES/STRANDS

Besidesthe designrequirements,additional cables/strandsshallbesymmetricallyplacedin thestructuresoasto be capableof generatingprestressingforce of about4 per centof the totaldesignprestressingforce in the structure. Only those cableswhich arerequiredto makeup the deficiency shall be stressedandtheremainderpulled out andtheducthole shall be grouted.

23. STORAGE AND HANDLING OF PRESTRESSINGMATERIALS

A recommendedpractice for storage and handling ofprestressingmaterial is given in Appendix-3.

24. PRESTRESSINGOPERATION

A recommendedpractice for prestressingoperationsisgiven at Appendix-4.

25. GROUTING OF CABLES

A recommendedpracticefor groutingof cable is given atAppendix-5.

38

IRC: 18-2000

Appendix-lA

TESTS ON SHEATHING DUCTS

(1) All tests specified below shall be carried out on the samesamplein the order given below.

(2) At least3 samplesfor one lot of supply(not exceeding7000metre length) shall be tested.

3. WORKABILITY TEST

A testsample1100 mm long is solderedto a fixed baseplatewith asoft solder(Fig. lA-I). The sampleis then bent to a radius of 1800 mmalternatelyon either side to complete3 cycles.

Thereafter,the sealingjoints will be visually inspectedto verify thatno failure or opening has takenplace.

4. TRANSVERSE LOAD RATING TEST

The test ensures that stiffness of the sheathingis sufficient to preventpermanent distortion during site handling.

The sample is placedon a horizontalsupport500 mm long so that thesample is supportedat all points of outward corrugations.

A loadasspecifiedin Tablebelow is appliedgradually at the centreof the supportedportion througha circular contactsurfaceof 12 mm dia.Couplers shall be placed so that the load is applied approximatelyat thecentre of two corrugations, Fig. I A-2. The load asspecified below is appliedin increments.

39

IRC

:18-2000

aS

<I—

U

40

ciD~ ~ — 2S,2S.1 M~.

cc

Fig. IA-2. Transverseload rating test

Table

IRC: I 8-2000

more than more than more than more than more than more thanDia 25 mm 35 mm 45 mm 55 mm 65 mm 75 mm 85 mm

to up to up to up to up to up to tip to35 111111 45 mm 55 mm 65 mm 75 mm 85 mm 90 mm

Load: 25ON 400N 500N 600N 700N 800N 1000 N

The sample is consideredacceptableif the permanentdeformationisless than S per cent.

EL EVAT~ON

•~9PPLAIt 4�O.240,lO

$

5cc

LL&s— A MPLcrt po.1w,i:

.L

ILA

41

}RC 18-20005. TENSION LOAD TEST

The test specimen is subjected to a tensile load. The hollow core isfilled with a woodencircular piece having a diameterof 95 per cent of theinner dia of the sample to ensure circular profile during test loading,Fig. IA-3.

MSPLATC I5Og~5Oi6O

SOFT SOLOULD JOUT

LONG

WOODEN CYUNORICAL MESSLA~ OF ~5fl ~*1E~ D~AM(TZ~OF

L5~Afl~0

SOFT SOLD�R~DJ0~NT/

/MS pL~’.r( 00. 00. ~O

Fig. IA-3. Tension toad test

A coupler is screwedon and the sampleloaded in increments,tillspecified load. If no deformationof the joints nor slippage of couplers is

NCH~ HOOK

-- SI.~CATHINOPIPI 1100

A

42

1RC: 18-2000

noticed, the test shall be consideredsatisfactory

Dia in mm Load

25 to 35 300 N

35to45 SOON

45to55 800N55to65 llOON

65 to 75 1400 N

75 to 85 [600N

85 to 90 1800 N

6. WATER LOSS TEST

Thesampleis sealedat oneend.The sample is filled with water andafter sealing,the endis connectedto a system capable of applying a pressureof 005 MPa, Fig. IA-4 and kept constant for 5 minutes, hand pump andpressuregaugeor stand pipe systemcanbe used.

Fig. 1A-4. Test for water lossstudy

PVC TL~( ~ G ~e~sCTDTO A PRES5URE OF O.~MPaRY PVP4P/ WATER HEAD FOR5 P.W~UTE5

P~CTUSE A~RVENT~ LONG

I. 1100•HS*TNIRQ I~MPLI LtNø~H

43

IRC: 18-2000

The sample is acceptable if the watertossdoesnot exceed 1.5 per cent

of the volume. The volume is worked out as follows:

Anothersample 500 mm long is sealed at one end and the volume ofhollow spacearrived at by pouring water from a measuringcylinder.

The computation of relative profile volume is worked out as follows:

- Premeasuredquantity of waterin a measuringcylinder

- Balance quantity of water left in the cylinder after

completely filling of the test sample

Actual Volume ‘V’ = V - Vp a 1,

Relative Profile Volume = V - A... cm3/cm2irçSl

Where / is length of specimenand 0 internal nominal dia. ofsheathing,

44

IRC: 18-2000

Appendix-lB

TESTS ON CORRUGATED HDPE SHEATHING DUCTS

Theadditionalacceptancetestsfor theprestressingsystemsemployingcorrugatedHDPE ductsshall cover the following two tests:

1. BOND TEST

Object:To establishsatisfactorybondcharacteristicsbetweenthe tendonandconcrete,in the ultimatecondition.

Equipment

* 3 nos.similar reinforcedconcretebeamswith a HDPE duct of

length equalto 40 times the duct diameter,

* Prestressingtendonof adequatelength for stressingand for

embeddingin the beam,

* Tendonanchoragesystem,

* Load cells and meters,

* Grout constituents.

Method: Cast an adequatelyreinforcedbeamto withstandthe prestressingoperationandof lengthto embed40 timesthe dia. of duct to suit thetendonto be adopted.Introducethe strandsof the tendonby spacingthem parallelby meansof ply-spacersasshown in Fig. lB-i and fill the duct with groutof strength not less than 27 N/sq.mm. When the grout has attainedthenecessarystrength,stressthetendonslowly increasingthe load to the failurecapacity. The failure capacity of the bond shall be at least equal to theanchorageefficiencyor 0.95 of failure capacityof the tendon.At least3 nos.of tests shall be carried out to ascertain the adequacyof the duct.

2. COMPRESSIONTEST FOR THE LOSS OF WALLTHICKNESS

Object: To establishthe wear and tear of the sheathingmaterial and therigidity of theductsurfaceagainstindentationandabrasionunderconcentratedline loading from the tendonconstitutents.

45

IRC: 18-2000

Pt~SPA~5RWSS~AS R~J4RED

jf)IJ~ SQUARE P~Y~OD= lSU~(GR~JT PANELS 2 NOs.

Equipment:

* 3 nos. of concreteblocks

* 1 no. of 1000 mm {ong strandforming the tendon

* A3M~Npress

* A loading beamof 300 mm length to transmit5 kN load

* A rubber pad for placing between the press and the beam for

uniform and constantload transfer

* A bearingplatewith a monostrandjackto pull the strandunder

loadedcondition

* A digital calliper

Fig. lB-i. Bond test arrangement

46

IRC: 18-2000Method: Cast3 nos. of concretecubesof 300 mmsize, of thesamestrengthas of main structure,with half cut HDPE sheathingductsembeddedin it atthe topas shown in Fig. IB-2. Careshallbeexercisedto ensurethat the ductsurface has uniform contact with concreteall around. Placethe concreteblock over the press with a 1000 mm length of strand forming the tendonplaced in the duct and apply the S kN uniform load gradually asshown.Pullthe strand under the stressedcondition by 200 mm across the duct. Repeatthe test on all the 3 nos. of ducts so embedded. Measure the indentationsformed in all the 3 nos.of ducts along the length of the strand, by means ofdigital calliper. The residual thickness of the duct shall not be less than 1 .5mm.

LOAD 5~N ~LOADING ROAM

S NO.

I~. __SIDE VIEW END VIEW

-OGflJL CaLIPER

ENLARGED VIEW OF WEAR DEPTH MEASUREMENT

Fig. I B-2. Compressiontest arrangement

47

IRC: 18-2000

Appendirc-2

SPECIFICATION FOR SHEATHING DUCT JOINTS

The sheathingducts shall be of the spiral corrugatedtype. For majorprojects,the sheathingductsshouldpreferablybe manufacturedattheprojectsite utilising appropriatemachines.With suchan arrangement,long lengthsof sheathingductsmay be usedwith consequentreductionin the numberofjoints andcouplers.

Where sheathing duct joints areunavoidable,suchjoints shallbemadecementslurry tight by the useof corrugatedthreadedsleevecouplerswhichcan be tightly screwedon to the outer side of the sheathingducts.A heat-shrink couplercould also be used if suitable.

Typical details of a sleeve coupler is shown in Fig. 2.1. The length ofthe couplershouldnotbe lessthan 150 mm butshouldbe increasedupto 200mm whereverpracticable.The joints betweenthe endsof thecouplerandtheduct shall be sealedwith adhesivesealing tape to preventpenetrationofcementslurry during concreting. The couplersof adjacentductsshould bestaggeredwhereverpracticable.As far as possible,couplersshouldnot belocated in curved zones.The corrugated sleeve couplers are being convenientlymanufactured using the sheath making machine with the next higher size ofdie set.

Fig. 2.1

The heat-shrinkcouplerFig. 2.2 is suppliedin the form of bandagerolls which canbe usedfor all diametersof sheathingducts.The bandageis

ISO .i.~

20 ~.(‘1!)

48

IRC: 18-2000

coatedon the undersidewith a heat sensitiveadhesiveso that after heatingthe bandagematerialshrinks on to thesheathingductandensuresformationof a leakproofjoint, without theneedforextrataping or supportin the formof corrugatedsleevecouplers.The heatingis effectedby meansof asoft gasflame.

~_.._ SOism_4

Fig. 2.2

d1~fz

49

IRC: 18-2000

Appendix-3

RECOMMENDED PRACTICE FOR STORAGES ANDHANDLING OF PRESTRESSING MATERIAL

All prestressingsteel,sheathing,anchoragesandsleevesor couplingsshall be protectedduring transportation,handling and storage.Forwires upto 5 mm dia, coils of about1.5 m dia, and for wires above5mm dia, coils of about 2 m dia without breaksand joints shall beobtainedfrom the manufacturer.

2. Materialsshall be storedin accordancewith the provisionscontainedin relevant specifications. All efforts shall be made to store thematerials in proper places so as to prevent their deterioration orintrusion by foreign matterand to ensuretheir satisfactoryquality andfitness for the work. The storage space shall also permit easyinspection,removalandre-storageof the materials.

3. The prestressingsteel,sheathingandotheraccessoriesshallbe storedundercoverandprotectedfrom rainor dampground.Theseshall alsobe protected from the ambient atmosphereif it is likely to beaggressive.All prestressingsteel shall be provided with temporaryprotection during storage such as coating of soluble oils, silica gel orvapour phaseinhibiting materialsof provenspecifications.

4. Storageat site shall be kept to the absoluteminimum. All materialseven though stored in approved godowns shall be subjected toacceptancetest prior to their immediateuse.

50

IRC: 18-2000Appendix-4

RECOMMENDED PRACTICE FORPRESTRESSI~~GOPERATIONS

Prestressingoperationandgroutingshall beentrustedto only speciallytrained and qualified personnel. All prestressingaccessoriesshall beprocured from authorisedmanufacturerswith in-house testing facilities.Contractors shall also be required to engage specialised agencies who shouldalso be entrustedwith the total servicecontract for fabrication of cables,protection of cables during concreting, prestressing and grouting. Necessarycertificatesshall alsobeaccordedby suchspecialisedagenciesthat the workhas been carried out in accordance with prescribed specifications. Inexceptional cases where the client is convinced that the contractor of thebridge itself is well experienced and has qualified personnel and sufficienttrack record to substantiate his performance in the particular system ofprestressingbeing adopted, the prestressingandgroutingoperationscouldbeentrusted to the contractor.

51

IRC: 18-2000

Appendix-S

RECOMMENDED PRACTICE FOR GROUTING OFPOST-TENSIONED CABLES IN PRESTRESSED

CONCRETE BRIDGES

I. GENERAL

The recommendationscover the cementgroutingof post-ten~ionedtendonsof prestressedconcretemembersof bridges. This alsocoverssome of the essentialprotectivemeasuresto be adoptedforminimising corrosionin PSC bridges.

1.2. The purposeof grouting is to provide permanentprotectionto thepost-tensionedsteel againstcorrosionand to developbond betweenthe prestressingsteel and the surroundingstructuralconcrete.Thegrout ensuresencasementof steel in an alkaline environmentforcorrosionprotectionandby filling the duct space,it preventswatercollectionand freezing.

2. MATERIALS

2.1. Water

Only cleanpotablewaterfree from impuritiesconformingto Clause3.3 of this criteria shallbe permitted.No seaor creekwater is to beused at all.

2.2. Cement

Ordinary PortlandCementshould be used for preparationof thegrout. It should be as fresh as possibleand free from any lumps.Pozzolanacementshall not be used.

2.3. Sand

It is not recommendedto use sand for grouting of prestressingtendons.In casethe internal diameterof theducts exceed150 mm,useof sand may be considered.Sand, if used,shall conformto IS:383 andshall passthroughIS SieveNo. 150. The weightof sand inthe grout shallnot be morethan 10 per centof theweightof cement,unlessproper workability can be ensuredby addition of suitableplasticizers.

52

IRc: 18-2000

2.4. Admixtures

Acceptableadmixturesconformingto IS: 9103 may be usedif testshave shown that their use improves the propertiesof grout, i.e.increasingfluidity, reducingbleeding, entrainingair or expandingthegrout. Admixturesmustnotcontainchlorides,nitrates,sulphides,suiphitesor any otherproductswhich are likely to damagethe steelor grout. When an expandingagentis used,the total unrestrainedexpansionshouldnot exceed10 per cent. Aluminium powderas anexpandrngagent is not recommendedfor groutingbecauseits longterm effects are not free from doubt.

2.5. Sheathing

2.5.1. For specificationssheathing,Clause 3.6 of this criteria may bereferredto.

2.5.2. Grout openings or vents

(a) All ducts should have grout opening at both ends, For thispurpose special openings should be provided where suchopenings are not available at end anchorages.For draped(curved)cablescrown points should have a grout vent. Fordrapedcableslonger than SOm grout ventsor drain holes maybe providedat or nearthe lowest points.It is a goodpracticetoprovide additional air vents at suitable intervals. All groutopenings or vents should include provisions for preventinggrout leakage.

(b) Standarddetailsof fixing couplers,inlets, outletsandair ventsto the duct/anchorageshallbe followedasrecommendedby thesupplierof the systemof prestressing.

2.5.3. I)uctsshouldbe securelyfa~tenedat closeintervals.All unintendedholes or openings in the duct must be repairedprior to concreteplacing.Thejoints of the couplersandthesheathingshouldbe madewater proof by use of tape or similar suitable systemcapableofgiving leakproofjoints. Grout openingsandventsmustbe securelyanchoredto the duct and to either the forms or to reinforcing steelto preventdisplacementduring concretingoperationsdueto weight,buoyancyandvibrations,

53

IRC: 18-2000

2.5.4. Duetsrequirevery carefulhandlingas,beingof thin metal,they aresusceptibleto leakagedue to corrosion in transit or storage,bytearing ripping in handling particularly when placed adjoining toreinforcingsteel,by pulling apartof joints while inserting tendonsprior to concreting,or by accidentalpuncturingwhile drilling forform ties/inserts.Ducts are also liable to damageby rough use ofinternal vibrator and sparksfrom welding being done close by.

3. EQUIPMENT

3.1. Grout Colloidal Mixer

It is essentialthat the grout is maintainedin ahomogenousstateandof uniform consistencyso that there is no separationof cementduring entire grouting process.It is, therefore,necessarythat thegrout be continuouslymixed in a colloidal mixer with a minimumspeedof 1000RPM andtravel of dischargenotexceeding15 m persecond.

3.2. Grout Pump

The pump should be a positive displacementtype and should becapableof injecting thegrout in a continuousoperationand not bywayof pulses.Thegroutpumpmust be fitted with a pressuregaugeto enable pressureof injection to be controlled. The minimumpressureat which grout shouldhepumpedshall be0.3 MPaandthegrout pumpmusthavea relief arrangementfor bypassof the groutin caseof build up of pressurebeyond 1 MPa. The capacityof thegrout pump shouldbe such as to achievea forward speedof groutof around5 to 10 metresperminute. Theslowerratesare preferableasthey reducethepossibility of occurrenceof voids. If the capacityof the pump is large, it is usual to grout two or more cablessimultaneouslythrougha commonmanifold.

Use of hand pumps for grouting is not recommended.Use ofcompressedair operatedequipmentfor injection is prohibitedas itis likely that therewill be some air entrappedin grout.

3.3. Water Pump

Before commencementof grouting, a stand by direct feed highpressurewater pumpshould be available at site for an emergency.

54

IRC: 18-2000

In case of any problem in grouting the ducts, such pump shallimmediatelybe connectedto the duct andall grout flushedby useof high pressurewater flushing. It is, therefore,necessaryto haveadequatestorageof cleanpotablewater for operationof the waterpump for suchemergencies.

3.4. Grout Screen

Thegroutingequipmentshouldcontaina screenhaving a meshsizeof IS: 106 (TS:l50 if sand is used).Prior to introduction into thegrout pump, the grout shouldbe passedthroughsuch screen.Thisscreenshould be easily accessiblefor inspectionandcleaning.

3.5. Connectionsand Air Vents

Standard details of fixing inlets, outlets, and air vents to thesheathingandloranchorageshouldbe followed as recommendedbyspecialistsupplier of the systemof prestressing.In general, allconnectionsare to be of the “Quick couple” type andat changeofdiameterssuitable reducersare to be provided.

4. PROPERTIES OF THE GROUT

4. 1. Water/cementratio should be as low as possible,consistentwithworkability. This ratio shouldnot normally exceed0.45.

4.2. The temperatureof the grout after accountingfor the ambienttemperatureof the structureshall not exceed25°C.

4.3. Before grouting, the propertiesof the grout mix shouldbe testedina laboratory dependingon the facilities available.Tests should beconducted for each job periodically. The recommendedtest isdescribedbelow.

4.3.1. Compressivestrength:The compressivestrengthof 100 mm cubesof the groutshall not be lessthan 17 MPa at 7 days.Cubesshall becuredin a moist atmospherefor the first 24 hoursand subsequentlyin water.Thesetestsshall be conductedin advanceto ascertainthesuitability of the grout mix.

55

1RC: 18-2000

5. MIXING OF GROUT

5.1. Proportionsof materialsshouldbebasedon field trials madeon thegrout beforecommencementof grouting, but subject to the limitsspecifiedabove,The materialsshouldbe measuredby weight.

5.2. Water should be addedto the mixer first, followed by portlandcementand sand, if used. Admixture, if any, may be addedasrecommendedby the manufacturer.

5.3. Mixing time dependsupon the type of the mixer but will normallybe between2 and 3 minutes.However,mixing shouldbe for sucha duration as to obtain uniform and thoroughly blendedgrout,withoutexcessivetemperatureincreaseor lossofexpansivepropertiesof the admixtures.The grout shouldbe continuouslyagitateduntilit is injected.

5.4. Once mixed, no water shall be addedto the grout to increaseitsfluidity.

5.5. Handmixing is not permitted.

6. GROUTING OPERATIONS

6.1. General

(a) Grouting shall be carriedout as earlyaspossiblebut not laterthan 2 weeksof stressinga tendon.Wheneverthis stipulationcannot be complied with for unavoidablereasons,adequatetemporaryprotectionof the steelagainstcorrosionby methodsor productswhich will not impair the ultimateadherenceof theinjected grout should be ensuredtill grouting. The sealingofthe anchorageendsafter concretingis consideredto be a goodpractice to preventingressof water.Forstructuresin aggressiveenvironment,sealingof the anchorageendsis mandatory.

Notes: 1. Application of some patentedwater soluble oils forcoating of steelfVPl powder injection/sendingin ofhot, dry, oil-free compressedair through the vents atfrequentintervals haveshownsome good results.

2. Some of the methodsrecommendedfor sealing ofanchorages are to seal the openings with bitumen

56

IRC: 18-2000

impregnatedgunny bag or water proof paperor bybuilding abrickpedestalplasteredon all facesenclosingthe exposedwires outsidethe anchorages.

(b) Any tracesof oil if applied to steel for preventingcorrosionshould be removedbeforegrouting operation.

(c) Ducts shall be flushedwith water for cleaning as well as forwetting thesurfacesof the duct walls. Waterusedfor flushingshouldbeof samequality as usedforgrouting. It may,however,containabout1 percentof slakedlime or quick lime. All watershouldbe drainedthroughthe lowest drain pipe or by blowingcompressedair throughthe duct.

(d) The water in the duct should be blown out with oil freecompressedair.

Blowing out water from duct for cables longer than 50 indraped up at both ends by compressedair is not effective,outlet/ventprovidedat or nearthe lowestpoint ~ha1lbe usedtodrain out water from duct.

(e) The connectionbetweenthe nozzle of the injection pipe andduct should be such that air cannot be sucked in.

(f) All outlet points including vent openings should be kept openprior to commencementof injection grout.

(g) Before grouting, all air in the pump and hose should beexpelled.The suctioncircuit of thepumpshould be air-tight.

6.2. Injection of grout

(a) After mixing, the grout should be kept in continuousmovement.

(b) Injection of grout must be continuous and should not be

interrupted.(c) For vertical cable or cables inclined more than 60° to the

horizontalinjection shouldbeeffectedfrom thelowestanchorageor vent of the duct.

(d) The methodof injection should ensurecompletefilling of theducts.To verify this, it is advisableto comparethe volume of

57

IRC: 18-2000

thespaceto be filled by the injectedgroutwith the quantityofgrout actually injected.

(e) Groutingshouldbe commencedinitially with a low pressureofinjection of upto0.3 MPa increasingit until the groutcomesoutat the other end. The grout should be allowed to flow freelyfrom the otherenduntil theconsistencyof the grout at this endis the sameas that of the grout at the injection end. When thegrout flows at the otherend, it shouldbe closedoff andbuildup of pressurecommenced.Full injection pressureat about0.5MPa shall be maintainedfor at leastoneminute beforeclosingthe injection pipe. It is a recommendedpracticeto provide astandpipe at thehighestpoint of the tendonprofile to hold allwaterdisplacedby sedimentationor bleeding.If there is a buildup of pressuremuchin excessof I MPa without flow of groutcoming at the other end, the grouting operation should bediscontinuedand the entire duct flushed with high pressurewater, Also, the bypasssystem indicatedin para 3.2 above isessentialfor furthersafety.

(0 In the case of cables draped downwards e.g. in cantileverconstruction simultaneousinjection from both ends may beadoptedFig. 5.1.

(g) Grout not usedwithin 30 minutesof mixing shouldbe rejected.

(h) Disconnectionis facilitated if a short length of flexible tubeconnectsthe duct and injectionpipe.Thiscan besqueezedandcut off after the grout hashardened.

7. PRECAUTIONS AND RECOMMENDATIONS FOREFFECTIVE GROUTING

(a) In cold and frosty weather, injection should be postponedunlessspecialprecautionsare taken. If frost is likely to occurwithin 48 hours after injection, heat must be applied to thememberandmaintainedfor at least48 hoursafter injection sothat the temperatureof the grout doesnot fall below 5°C.Priorto commencementof grout, caremust be takento ensurethatthe duct is completely free of frost/ice by flushing with warmwater, but not with steam.

58

IRC: 18-2000

(b) When the ambient temperatureduring the day is likely toexceed40°C,grouting shouldbe done in the earlymorningorlate eveninghours,

(c) Whenthe cablesare threadedafter concreting,the ductmustbetemporarilyprotectedduring concretingby inserting a stiff rodor a rigid PVC pipe or any other suitable method.

(d) During concreting, care shall be taken to ensure that thesheathingis not damaged.Needlevibrators shall be usedwithextremecareby well experiencedstaffonly, to ensuretheaboverequirements.

(e) It is a good practice to move the cables in both directionsduring the concretingoperations.This can easily be done bylight hamnieringtheendsof thewires/strandsduringconcreting.It is also advisablethat 3 to 4 hoursafter concretingthe cableshouldbemovedbothwaysthrougha distanceof about20 ems.With such movement,any leakageof mortarwhich has takenplace in spiteof all precautions,losesbond with thecables,thusreducingthe chanceof blockages.This operationcan also bedoneby fixing prestressingjacksat one endpulling the entirecableand then repeatingthe operationby fixing thejack at theotherend.

(0 The cables to be grouted should be separatedby as muchdistanceas possible.

(g) In caseof stageprestressing,cablestensionedin the first stageshouldnot remainungroutedtill all cablesare stressed.It is agood practice,while groutingany duct in stageprestressing,tokeepall the remainingductsfilled up with water containing Iper cent lime or by running water through suchducts till thegrout has set. After grouting the particularcable,the water intheothercablesshouldbedrainedandremovedwith compressedair to preventcorrosion,

(h) Careshould be takento avoid leaks from oneduct to anotherat joints of precastmembers.

(i) End faceswhere anchoragesare locatedare vulnerablepointsof entryof water.Theyhaveto be necessarilyprotectedwith an

59

IRC 18-2000

O~I~T~O~IVII .~TEOAT~

~TO . ~

- ..- :____~.~__~~____._... ..__~.1‘~-~

2 11J ~T ~I~JAT~B

,~

2 ~Oth~1~ ~ffIP~ S~Jt.TN~~IJ~NF~~ ~iT~TE Pt.L~ 41 4TIR4M.S

~ ~tOP_~

.—~—---—~--

~Th D~STO a~ ~

~ ~~

4 ET.~.5~ ~‘WL. ..jim T~’JL.~ ~TI4

.---~----~-

° 4~uL..MTtR 4tOV~C TOIl ~ TOP ~�N1 [A~S ~ ~ ~ ~t~tD~ ~ V~ 1W orm~ _

~ Ft~I P~ç~TTT21 m4TT

~ __4 4 L2RTOfl ~ 10 FH~ F~4& TOP ~Il STOP Pt~ Mm ~UPT

~ O1WR . P O.D4 ~TSR F~LO~SF

7 ~ ~FEM lOP .~NI

4 .N.Us ~iL ~ ~lQ .,..J ~ ~O]~

Fig. 5.1, Procedurefor grouting of cables draped downwords

60

IRC: 18-2000

effective barrier. Recessesshould be packed with mortar

concreteand should preferably be painted with water proofpaint.

(j) After groutingis completed,the projecting portionof the ventsshould be cut off and the faceprotectedto preventcon’osion,

61