PSC Girder vs Steel Girder
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Author Message
G.Radhakrishnan
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Joined:May11,2010No.of
Replies:488
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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Joined:May14,2007No.of
Replies:838
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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Joined:May11,2010No.of
Replies:488
Posted:MonSep26,20118:50am
Regrettedtohighlightthatwithoutdevelopingsuitableguidelinesforinspection&maintenance,wehaveswitchedovertoPSCgirders!andmostofthesteelgirderbridgeshavebeenconvertedintoPSC.
GeneralcommentduringinspectionisWhatistheretoseeinPSCwhencomparedwithsteelwithoutconsideringtheconsequences!!
RecentlyconstructedPSCgirderbridgesduringGChavestartedgivingsymptomsabouttheirhealth.NextgenerationwillhavetofacealotofproblemswithpoorqualityPSCgirders.Atthattime,anewtechnologymaybeimplementedinlieuofPSCandlikeourearlysteelgirdersallPSCgirdersconstructedbeforexxxxxshallbereplaced!!!G.Radhakrishnan...260911
RAMKUMARSINGHDyCVO
(Engg)/SECR
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Replies:20
Posted:TueSep27,201112:19pm
Railwayhasrealisedtheproblemsoonandhasagainshiftedtosteelgirdersforspanmorethan24.4m.RAMKUMARSINGHDy.CE/BR/Splworks/SECR/BSP...270911
G.Radhakrishnan
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Joined:May11,2010No.of
Replies:488
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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Joined:May14,2007No.of
Replies:838
http://www.rdso.indianrailways.gov.in/uploads/files/1296817034676bs_36.pdfNarasimhaMurtyGannavarapuEXECUTIVEENGINEER(CON)...300911
G.Radhakrishnan
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Joined:May11,2010No.of
Replies:488
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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Replies:1674
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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Joined:May11,2010No.of
Replies:488
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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Joined:May11,2010No.of
Replies:488
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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Joined:Dec21,2009No.of
Replies:15
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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Joined:May11,2010No.of
Replies:488
(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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Joined:May14,2007No.of
Replies:838
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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