psc girder vs steel girder

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G.Radhakrishnan

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Posted:SatSep24,20119:38am

Thoughsteelgirdersarerequiredtobemaintainedperiodically,thosearefarbetterinviewofsafetywhencomparedwithPSCgirders.Thosewhoarecreatingassetsarenotboundtomaintainthesameinoursystem,likeOpenline&Construction.Qualityofworksdiffersfromcontractorstocontractors,EngineerstoEngineers,PlacetoPlaceetceventhoughtheSpecifications,Codes,Manualstobefollowedaresame.

Themainadvantagesinsteelgirdersviz,problemslikecorrosioncanbeovercomewithprotectivecoating,possibilitiesofstrengtheningwhereverorwheneverorwhateverrequired,easyreplacementbysteelgirdersifitwarrants,temporarygirdersofsimilarspansavailableincaseofemergenciesetc

ThespanofPSCgirdersmostlyarenotmatchingwiththeconventionalsteelgirderspanof12.2,18.3,24.4,30.5etc.IfanyPSCgirderfailsthealternatearrangementisnotconfinedbutweknowfailureinPSCwillbeasudden.

InourZone,conceptofprovidingPSCgirdersinplaceofsteelgirdersduringGCis100%implementedresultingsteelgirderbridgesinMGhavebeenrebuiltwithPSCinBG.

Withinshortperiodoftime,wearefacingleachingproblemsinPSCgirders(wateriscomingfromthedeckslabtobottomofPSCsolidgirders)whichwillleadtocorrosionintendonsalsoandfailureinnearfuture.

Duetononavailabilityofbridgestaff(Nointakeforaquitelongperiod)SSE/Bridgesareengagingcontractsystemforinspectionalso.(IhaveseensuchtendersinSWR)Noticingtheproblemsitselfnowbecomingaquestionmark

Atthisjuncture,whataretheprecautionstobetakenincaseof

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failureoremergenciesinPSCgirderbridges?Also,whataretheremedialmeasuresbeingadoptedincaseofsuchleachingproblemsanywhere?G.Radhakrishnan...240911

NarasimhaMurtyGannavarapuDy.General

Manager(civil)/RVNL

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Posted:SatSep24,20116:01pm

Inthegoodoldendays,forhigherspans,steelgirderswerepredominantlyused.Aftertheadventofprestressedconcrete,itsuseinhigherspanbridgesincreasedtremendously.MainreasonbehinduseofPSCgirdersisduetoitsinitialeconomicalcostMainreasonsfornotpreferringsteelgirderbridgesare:(i)Itsinitialcostismore.(ii)Itrequiresrecurringexpenditureinpainting.IncontrarytothatitisbelievedthatPSCgirdersarecheaperanddoesnotrequireanytypeofmaintenance.OnemoremeritofPSCGirderBridgeisaboutitsfacilityofprovidingthesametrackstructurelikeinapproaches.Demerits:AsfarasdemeritsofthePSCgirdersareconcerned,theseare(i)Brittlefailurenature.(ii)Lesslife.(iii)Verydifficultstrengthening/repair/restorationConcreteisbrittleinfailure.Itfailsallofasuddenwithoutgivinganywarning.FailureofMondoviBridgeatGoaisaburningexample.Contrarytothis,steelgirderswhichareductileinnaturegivesamplewarningsbeforefailure

Sinceconcreteisverystrongincompression,PSCconstructionhasgainedmomentum.ButunlikeRCC,PSCrequireslotofqualitycontrol.Highdurabilityhastobemaintainedduringconstruction.Thegirdershouldbeimpervious.otherwisewaterwillpercolateintothemember.Sincethecablesareheavilystressedtheywillpronetocorrosionatafasterrateduetoingressedwater.SriRadhakrishnanhasquotedthatthegirdersareleakingheavilyindicatesthepoorqualityinconstructionwhichwillspoilthegirderswithinshortperiod.Remedies:(i)Observingthecamberatregularintervalsinordertoknowthesoundnessofthegirder.(ii)Ifsubstantialdecreaseincamberisnoticed,externalprestressingistoberesortedthroughfuturecablels.(iii)Ifanylossofprestressistakenplace,itcanbenoticednearendblocksintheformofshearcracksat45angle.Henceendblockshavetobeobservedcperiodically.

RailwayBoardvidetheirletterNo.2005/CE1/BR11/8dtd28.05.2009hasinstructedtoadoptsteelgirdersforspansmorethan24.40m.ThereasonsasmentionedintheBoard,sletterare(1)TherearenodetailedguidelinesforinspectionanddefectsidentificationofPSCgirders(ii)Incaseofanyeventualityonsuchbridges,Rly.donothaveanyimmediatetemporaryrestorationmeasuresavailbleupto80ft.temporaryspanarrangements.(iii)AtthesametimesteelbridgesareknowntohavelongerlifethanothersandIRhavemanynumberofexamples.NarasimhaMurtyGannavarapuEXECUTIVEENGINEER(CON)...240911

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G.Radhakrishnan

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Posted:MonSep26,20118:50am

Regrettedtohighlightthatwithoutdevelopingsuitableguidelinesforinspection&maintenance,wehaveswitchedovertoPSCgirders!andmostofthesteelgirderbridgeshavebeenconvertedintoPSC.

GeneralcommentduringinspectionisWhatistheretoseeinPSCwhencomparedwithsteelwithoutconsideringtheconsequences!!

RecentlyconstructedPSCgirderbridgesduringGChavestartedgivingsymptomsabouttheirhealth.NextgenerationwillhavetofacealotofproblemswithpoorqualityPSCgirders.Atthattime,anewtechnologymaybeimplementedinlieuofPSCandlikeourearlysteelgirdersallPSCgirdersconstructedbeforexxxxxshallbereplaced!!!G.Radhakrishnan...260911

RAMKUMARSINGHDyCVO

(Engg)/SECR

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Posted:TueSep27,201112:19pm

Railwayhasrealisedtheproblemsoonandhasagainshiftedtosteelgirdersforspanmorethan24.4m.RAMKUMARSINGHDy.CE/BR/Splworks/SECR/BSP...270911

G.Radhakrishnan

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Posted:WedSep28,20115:53am

Good.

InthemeantimeanumbersofPSCgirdershavebeenerectedwithspansmorethan24.4m

Specificguidelinesarerequiredtobeframedandcirculatedforinspection,maintenance,monitoringthenoticeddefects,methodofrecordingcamber,temporaryarrangements,actionincaseofemergenciesincludinglossofcamber,methodofreplacementincaseoffailureintheexistingPSCgirdersG.Radhakrishnan...280911

NarasimhaMurty

Posted:FriSep30,201112:38pm

Anarticleon"INSTRUMENTATIONTECHNIQUESTOMONITORLOSSOFPRESTRESSANDCORROSIONOFSTEELINPRESTRESSEDCONCRETE"canbeseeninthislinkwhichisusefulforbridgemaintenancewing:

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GannavarapuDy.General

Manager(civil)/RVNL

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http://www.rdso.indianrailways.gov.in/uploads/files/1296817034676bs_36.pdfNarasimhaMurtyGannavarapuEXECUTIVEENGINEER(CON)...300911

G.Radhakrishnan

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Posted:SatOct01,20113:09pm

FromtheabovequotedArticle,thefollowingsentencesarereproducedhere.

Concretestructuresaresupposedtogivetroublefreeandmaintenancefreeservice,ifconstructedproperly.Normally,durabilityaspectsareusuallylostsightof.Becauseofwhich,manytimes,concretestructuresdevelopdefectsduringtheirservice.

Itwillbeworthwhiletonotethatnodirectmethodisavailabletomeasurelossofprestress.

ItcanbenotedthatV.W.loadcellsystemissuitablefornewconstructionandnotforexistingbridge.

VibratingWireStrainGaugeissuitableforuseonnewaswellasexistingbridges.NotmuchofliteratureonactualuseofaboveinstrumentationsystemisavailableeitherinIndiaorabroad

Noinstrument/techniqueisavailable,atpresent,whichcanmeasuretheextentofcorrosionofsteel

ItwillnotbeincorrecttostatethattheinstrumentationofbridgesisstillataprimitivestageinIndia.

Hence,wecannotgoforinstrumentationofeachbridgeduetocostaffair,SERCorothersimilarorganizationtobeinvitedandalsoinstrumentationalonewillnotsolveourproblems.Wemayhavetogoforrehabilitation,strengtheningorreplacementafterinstrumentation.

Duetoleachingdefect,thereinforcementsincludingtendonswillcorrodewithaperiodoftimewhichwillleadtolossofprestress.Noinstrumentationisfurtherrequiredforcorrosionorlossofprestress.Whatwillbetheremedialaction,oncecorrosionstarted?

Insteelgirders,themainproblemiscorrosionwhichcanbecontrolled.Even,camberlossgirdersarestillsurvivinginothertopicsofthisforum.G.Radhakrishnan...011011

Posted:SunOct02,20119:16am

Therearefewthingstobeconsidered:

1.ThePSCgirdersarenotasfragileastheyarenormallypresumedtobe.Thesearedesignedasductilestructuresasthenormalsteel/RCCstructuresareandthecrackswillbethereinstructurefor

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V.B.SoodDirector(B&S)

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longtimebeforeactualcollapsetakesplace,exceptinthecasewhenthePSCtendonsarenotgroutedproperlyandsnapduetocorrosion.

2.Yes,theunderstandingofPSCgirdersisonlowersidetodesired,partlybecauseoflackoftrainingandpartlybecauseoflackofdifficultnatureofsubject.ButitcannotbesaidthatthesewereintroducedwithoutpreparationsasthewillhavetheproblemofchickenandeggsituationwhethertofirstconstructPSC,whichisamaterialofchoiceworldover,orfirstcreateawarenessandinspectionmethodology.IwouldsaythattheapproachwasOKthatwayandiftheorganizationcannotgetpeopletolearnthethingsin30years,thereisnoexcuseaboutanything.

3.Ourbridgemanagementisnotinthatgreatshape.Exceptforthesteelgirderinspectionandmanagement,whichtomeistheeasiesttolearnandmaster,wearelackinginalmostallaspects.Thefloodsandscourisaverymuchneglectedfield,substructureinspectionisajoke,underwaterinspectionshaveassumedsomesortofpriorityonlyafterkillingscoresofpeopleonthisaccount.AndthelesssaidaboutmodernfieldslikeNDT,thebetteritis.IhadanopportunitytoinspectsomeoldarchesandIsawoldinspectionrecordsfor25yearsorsoandwasastonishedtoseethedivergingviewsthatlearnedengineershavetakenovertheyearsandalmostnonehadgivenasolutionthatcouldrestorethebridgestoarespectableshape.Thismuchfortheoldesttypeofthebridgesthatweareusing.So,theissueofPSCisnotthatdirewhenseeninlightwithitsolderpeers.

4.TheproblemintheparticularcaseappearsduetotheslabconnectingtheIgirders.Theseslabsarethelastitemofconstructionandthetimeconstraintscancausetheproblemsmentioned.ButtheproblemwillmostlikelybeinRCCandnotPSCcomponents.Ifthisisthecase,youcancheerupasRCCisloteasiertomaintainandrehabilitatethanPSC,andalsothewatermightnotbeaffectingthetendons.WehaddealtwithsomesuchcasesonWRandIhadmadeafilmonthesamewhichcanbeseenhere:

http://wiki.iricen.gov.in/doku/doku.php?id=training_films

Iftheproblemisdifferent,pleaseletusknow.V.B.SoodDirector(B&S)...021011

G.Radhakrishnan

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Posted:WedOct05,201112:18pm

Inmycaseisdifferent.PSCsolidgirdersof10spansof9.14meachinabridgeconstructedduringtheyear1998,arehavingleachingdefect(fromthetopofdecktobottom)inalmostallthegirders.Seepageofwater,afterraining,canbevisuallyseen.Also,atthejunctionofretainingwallconnectingdeckslabinsomanybridgesincludingROBssuchleachingdefectswerenoticedG.Radhakrishnan...051011

Posted:WedOct12,20117:33am

InPSCboxgirders,theopenspacesaremisusedbypublic.IfoundthatonePSCboxgirderROBisusedasminiBAR.Shallweclosetheopeningsprovidedintheboxgirders.

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G.Radhakrishnan

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Onseeingsuchmischievouswegetwarningas"dangerahead!"G.Radhakrishnan...121011

A.P.MALIKCPM1

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Posted:WedOct19,20111:52pm

Therearemanyfactorsthatgointodecidingthematerialtobeusedinconstruction.Firstandforemostoftheseistherealityandfactsastheyexist,insteadofwhatwethinktheyshouldbeorassumethemtobe.Ourassumptionsmustasclosetorealityaspossible.

Andthefactis,PSCisnotthematerialforourbridges.Ourqualitycontrol,handlingequipments,maintenanceresourcesarenotfitforPSCgirders.Forspansof9.15mandabove,weshouldsticktosteelgirders,thetried,thetestedandtheelegantelements.ForsleepersoverthemwemayapproachSCtoallowtimbers,asvolumewouldbemuchlessnow,asforeverythingelsewehaveswitchedovertoPSCsleepers.

Unlikeroad,wecannotdiverttrafficatwill.Wegetverylimitedtimeforrepairsandreplacement.Anyfailures,unlikeinaroadbridge,arepotentialdisasterforus.Oursitesarewhereitisverydifficulttotakecranestohandletheweightsinvolved.Justtogiveyouanidea,totalweighttobehandledincaseofPSC9.15mspanis82tonnes(minimumcomponentweightbeing20/30T,dependingonwhetherpreorposttensioned)asgainstabout9tonnesfora9.15msteelspan.A.P.MALIKDyCPM/C/III...191011

AvijitMujumder

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Posted:TueOct25,20113:14pm

Apartfromabovedefficiencies,theheightofdeckincaseofPSCgirderisanotherdetrimentalfactorwhichcannotbeignoredastheapproachofbridgesistoberaised.Incaseoftallpiers,seismicloadsonheaviersuperstructure(PSCgirders)hasconsiderableeffectonsubstructure&it'sfoundation.AvijitMujumder...251011

Posted:MonNov21,20117:23am

ThetwomeritsmentionedbyEXECUTIVEENGINEER/CONfortheuseofPSCgirdersalsohavingthefollowingdisadvantages

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G.Radhakrishnan

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(i)TheMainreasonbehinduseofPSCgirdersisduetoitsinitialeconomicalcostisapplicablefornewconstructiononly.Inopenline,replacementofsteelgirderwithPSCgirderwillcostmoreduetoexpensivelaunchingscheme,prolongedspeedrestriction&megalineblock

(ii)OnemoremeritofPSCGirderBridgeisaboutitsfacilityofprovidingthesametrackstructurelikeinapproaches.But,withoutadheringthemanualprovisions,thesametrackstructureofapproach(LWR)hasbeencontinuedonthePSCgirderbridges.Ifanythinghappensthenonlyresponsibilitywillbefixedandalsocircularswillcome.So,PSCgirderfacilitatesformisleadingtheLWRmanualprovisionsG.Radhakrishnan...211111

NarasimhaMurtyGannavarapuDy.General

Manager(civil)/RVNL

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Posted:MonNov21,20114:52pm

Mr.Radhakrishnanhasexpressedviewinthemaintenancepointofview.Apartfromcertaindisadvantages,PSCgirdershavenumerousadvantagesalsoundoubtedly.Sincesteelgirdershadlonghistoryandstoodforthetestoftimeandmoreoverthesteelismanufacturedatsteelplantswithhighestqualitycontrol,nodoubttheyaresuperiorandstrongertoPSCgirders.Butthedisadvantagewiththemisthemaintainabilityoftrackoverthosegirders.LastdecadePWayEngineerssufferedalotonthatscore.ThenonlyPSCgirdershavecomeintopicture.RegardingreplacementofsteelgirderswithPSC,itisrestrictedupto6.10monlyandoverandabovetheywillbecastinsituonly.AsfarascontinuingofLWRoverPSCgirderbridgesareconcerned,certainRailwayshaveofficiallyundertakenthesameontrialbasisandaregivingbetterresults.OffcourseKonkanRailwayhasalreadycontinuedtheirallLWRsongirderbridgesprovidedwithbearingsandnoanyuntowardincidentshavebeennoticed.Manualsaresuggestiveonlyanddoesnotrestrictthebetterments.Duetothisflexibility,correctionslipsarebeingissuedasandwhenneeded.Afterallwethescientificandengineeringcommunityshouldalwaysthinkforbetterchangesandaccordinglyexperimentshavetobecontinued.GapsbetweensinglerailshavebeenprovidedforseveralyearswithaviewthatlinearexpansionwillcreateproblemsuntilLWRshavebeendiscoveredandproveditwaswrong.RutherfordsquantumtheoryregardingelectronsrevolvingroundthenucleuswasprovedwrongtillBohrsexperimentrevealedthattheywillrevolveinfixedorbitsafter60years.Thatissscienceandchangeswillalwaystakesplace.AsfarasPSCgirdersareconcerned,themainproblemwiththemiswiththequalityatsite.Theyrequirehighstandards.Veryfewcontractorsawareofthesameandtheythoughtthatqualityistheresponsibilityoftherailway.Unlikesteel,concreteisaheterogeneousmixandhastobemadeatsite,maintainingqualityandachievinguniformqualityisatoughesttaskfortheConstn.Engineers.Knowingallthesefacts,RailwayBoardhasrestricteditsuseupto24.40mgirders.NarasimhaMurtyGannavarapuEXECUTIVEENGINEER(CON)...211111

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G.Radhakrishnan

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Posted:MonNov21,201110:58pm

Ihavefocusedinmaintenancepointofviewonly.

InPambanBridge,wehavereplacedthePSC(MG)girderswithsteelgirdersbygantrymethod.

Steelgirderspansabove6.10marebeingconvertedintoPSCbyadoptingsuitablelaunchingschemeintrafficcondition.

PSCgirdersitselfmayrequirereplacement!

Betterchanges(inthematerialofconstruction)arealwayswelcome.Atthesametime,technologyformaintainingthesamealsotobedevelopeddulyconsideringthevulnerablefactorssuchasqualityofconstruction,environmentalcondition,workmanshipetc.,

Betterunderstandingisessentiallyrequiredwhenwechangeovertoanewsystem

Asmentionedthatveryfewcontractorsaretakingcareofquality,veryfewEngineersareworriedaboutqualityandhenceveryfewbridgesareingoodcondition

Concretestepsarerequiredtobetakentosafeguardourassetsofconcretebridges

Steelgirders>>>Concretegirders>>>Compositegirders>>>?G.Radhakrishnan...211111

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