1、BridgeresearchinEuropeAbriefoutlineisgivenofthedevelopmentoftheEuropeanUnion,togetherwiththeresearchplatforminEurope.Thespecialcaseofpost-tensionedbridgesintheUKisdiscussed.InordertoillustratethetypeofEuropeanresearchbeingundertaken,anexampleisgivenfromtheUniversityofEdinburghportfolio:relatingtothe
2、identificationofvoidsinpost-tensionedconcretebridgesusingdigitalimpulseradar.IntroductionThechallengeinanyresearcharenaistoharnessthefindingsofdifferentresearchgroupstoidentifyacoherentmassofdata,whichenablesresearchandpracticetobebetterfocused.AparticularchallengeexistswithrespecttoEuropewherelangu
3、agebarriersareinevitablyverysignificant.TheEuropeanCommunitywasformedinthe1960sbaseduponapoliticalwillwithincontinentalEuropetoavoidtheEuropeancivilwars,whichdevelopedintoWorldWar2from1939to1945.ThestrongpoliticalmotivationformedtheoriginalcommunityofwhichBritainwasnotamember.Manyofthecontinentalcou
4、ntriessawBritainsinterestasbeingpurelyeconomic.The1970ssawBritainjoiningwhatwasthentheEuropeanEconomicCommunity(EEC)andthe1990shasseenthewideningofthecommunitytoaEuropeanUnion,EU,withcertainpoliticalgoalstogetherwiththeobjectiveofacommonEuropeancurrency.Notwithstandingthesefinancialandpoliticaldevel
5、opments,civilengineeringandbridgeengineeringinparticularhavefoundgreatdifficultyinforminganykindofcommonthread.IndeedtheeducationalsystemsforUniversitytrainingarequitedifferentbetweenBritainandtheEuropeancontinentalcountries.TheformationoftheEUfundingschemes一e.g.Socrates,BriteEuramandotherprogramsha
6、vehelpedsignificantly.TheSocratesschemeisbasedupontheexchangeofstudentsbetweenUniversitiesindifferentmemberstates.TheBriteEuramschemehasinvolvedtechnicalresearchgrantsgiventoconsortiaofacademicsandindustrialpartnerswithinanumberofthestates一aBriteEurambidwouldnormallybeledbyanindustrialist.Intermsofd
7、isseminationofknowledge,twoquitedifferentstrandsappeartohaveemerged.TheUKandtheUSAhaveconcentratedprimarilyupondisseminatingbasicresearchinrefereedjournalpublications:ASCE,ICEandotherjournals.WhereasthecontinentalEuropeanshavefrequentlydisseminatedbasicresearchatconferenceswherethecirculationofthepr
8、oceedingsisrestricted.Additionally,languagebarriershaveprovedtobeverydifficulttobreakdown.IncountrieswhereEnglishisastrongsecondlanguagetherehasbeenenthusiasticparticipationininternationalconferencesbasedwithincontinentalEurope-e.g.Germany,Italy,Belgium,TheNetherlandsandSwitzerland.However,countries
9、whereEnglishisnotastrongsecondlanguagehavebeenhesitantPartiCiPantS一e.g.France.EuropeanresearchExamplesofresearchrelatingtobridgesinEuropecanbedividedintothreetypesofstructure:MasonryarchbridgesBritainhasthelargeststockofmasonryarchbridges.IncertainregionsoftheUKupto60%oftheroadbridgesarehistoricston
10、emasonryarchbridgesoriginallyconstructedforhorsedrawntraffic.ThisislesscommoninotherpartsofEuropeasmanyofthesebridgesweredestroyedduringWorldWar2.ConcretebridgesAlargestockofconcretebridgeswasconstructedduringthe1950s,1960sand1970s.Atthetime,thesestructureswereseenasmaintenancefree.Europealsohasalar
11、genumberofpost-tensionedconcretebridgeswithsteeltendonductspreventingradarinspection.ThisisaparticularprobleminFranceandtheUK.SteelbridgesSteelbridgeswentoutoffashionintheUKduetotheirneedformaintenanceasperceivedinthe1960sand1970s.However,theyhavebeenusedforlongspanandrailbridges,andtheyarenowreturn
12、ingtofashionformotorwaywideningschemesintheUK.ResearchactivityinEuropeItgivesanindicationcertainareasofexpertiseandworkbeingundertakeninEurope,butisbynomeansexhaustive.InordertoillustratethetypeofEuropeanresearchbeingundertaken,anexampleisgivenfromtheUniversityofEdinburghportfolio.Theexamplerelatest
13、otheidentificationofvoidsinpost-tensionedconcretebridges,usingdigitalimpulseradar.PosttensionedconcreterailbridgeanalysisOveArupandPartnerscarriedoutaninspectionandassessmentofthesuperstructureofa160mlongpost-tensioned,segmentalrailwaybridgeinManchestertodetermineitsload-carryingcapacitypriortoatran
14、sferofownership,foruseintheMetrolinklightrailsystem.Particularattentionwaspaidtotheintegrityofitspost-tensionedsteelelements.Physicalinspection,non-destructiveradartestingandotherexploratorymethodswereusedtoinvestigateforpossibleweaknessesinthebridge.SincethesuddencollapseofYnys-y-GwasBridgeinWales,
15、UKin1985,therehasbeenconcernaboutthelong-termintegrityofsegmental,post-tensionedconcretebridgeswhichmaybepronetobrittle5failurewithoutwarning.Thecorrosionprotectionofthepost-tensionedsteelcables,wheretheypassthroughjointsbetweenthesegments,hasbeenidentifiedasamajorfactoraffectingthelong-termdurabili
16、tyandconsequentstrengthofthistypeofbridge.Theidentificationofvoidsingroutedtendonductsatvulnerablepositionsisrecognizedasanimportantstepinthedetectionofsuchcorrosion.DescriptionofbridgeGeneralarrangementBesseso,th,BamBridgeisa160mlong,threespan,segmental,post-tensionedconcreterailwaybridgebuiltin196
17、9.Themainspanof90mcrossesoverboththeM62motorwayandA665BurytoPrestwickRoad.Minimumheadroomis5.18mfromtheA665andtheM62isclearedbyapprox12.5m.Thesuperstructureconsistsofacentralhollowtrapezoidalconcreteboxsection6.7mhighand4mwide.Themajorityofthesouthandcentralspansareconstructedusing1.27mlongpre-castc
18、oncretetrapezoidalboxunits,post-tensionedtogether.Thisboxsectionsupportstheinsiteconcretetransversecantileverslabsatbottomflangelevel,whichcarrytherailtracksandballast.Thecenterandsouthspansectionsareofpost-tensionedconstruction.Thesepost-tensionedsectionshavefivetypesofpre-stressing:1. Longitudinal
19、tendonsingroutedductswithinthetopandbottomflanges.2. Longitudinalinternaldrapedtendonslocatedalongsidethewebs.Thesearedeflectedatinternaldiaphragmpositionsandareencasedininsiteconcrete.3. Longitudinalmacalloybarsinthetransversecantileverslabsinthecentralspan.4. Verticalmacalloybarsinthe229mmwidewebs
20、toenhanceshearcapacity.5. Transversemacalloybarsthroughthebottomflangetosupportthetransversecantileverslabs.SegmentalconstructionThepre-castsegmentalsystemofconstructionusedforthesouthandcenterspansectionswasanalternativemethodproposedbythecontractor.Currentthinkingsuggeststhatsuchaformofconstructio
21、ncanleadto4brittle,failureoftheentirestructurewithoutwarningduetocorrosionoftendonsacrossaconstructionjoint,Theoriginaldesignconcepthadbeenforinsiteconcreteconstruction.InspectionandassessmentInspectionInspectionworkwasundertakeninanumberofphasesandwaslinkedwiththetestingrequiredforthestructure.Thei
22、nitialinspectionsrecordedanumberofvisibleproblemsincluding:1、 Defectivewaterproofingontheexposedsurfaceofthetopflange.2、 Watertrappedintheinternalspaceofthehollowboxwithdepthsupto300mm.3、 Variousdrainageproblemsatjointsandabutments.4、 Longitudinalcrackingoftheexposedsoffitofthecentralspan.5、 Longitu
23、dinalcrackingonsidesofthetopflangeofthepre-stressedsections.6、 Widespreadsaplingonsomeinsiteconcretesurfaceswithexposedrustingreinforcement.AssessmentThesubjectofanearlierpaper,theobjectivesoftheassessmentwere:1、Estimatethepresentload-carryingcapacity.2Identifyanystructuraldeficienciesintheoriginald
24、esign.3、 Detenninereasonsforexistingproblemsidentifiedbytheinspection.ConclusiontotheinspectionandassessmentFollowingtheinspectionandtheanalyticalassessmentonemiijorelementofdoubtstillexisted.Thisconcernedtheconditionoftheembeddedpre-stressingwires,strands,cablesorbars.Forthepurposeofstructuralanaly
25、sistheseelementshadbeenassumedtobesound.However,duetotheveryhighforcesinvolved,aarisktothestructure,causedbycorrosiontotheseprimaryelements,wasidentified.Theinitialrecommendationswhichcompletedthefirstphaseoftheassessmentwere:1. Carryoutdetailedmaterialtestingtodeterminetheconditionofhiddenstructura
26、lelements,inparticularthegroutedpost-tensionedsteelcables.2. Conductconcretedurabilitytests.3. Undertakerepairstodefectivewaterproofingandsurfacedefectsinconcrete.TestingproceduresNon-destructieradartestingDuringthefirstphaseinvestigationatajointbetweenpre-castdecksegmentstheobservationofavoidinapos
27、t-tensionedcableductgaverisetoseriousconcernaboutcorrosionandtheintegrityofthepre-stress.However,theextentofthisproblemwasextremelydifficulttodetermine.Thebridgecontains93jointswithanaverageof24cablespassingthrougheachjoint,i.e.therewereapprox.2200positionswhereinvestigationscouldbecarriedout.Atypic
28、alsectionthroughsuchajointisthatthe24drapedtendonswithinthespinedidnotgiverisetoconcernbecausethesewereprotectedbyinsiteconcretepouredWithoutjointsafterthecableshadbeenstressed.Asitwasclearlyimpracticaltoconsiderphysicallyexposingalltendon。Ointintersections,radarwasusedtoinvestigatealargenumbersofte
29、ndonsandhencelocateductvoidswithinamodesttimescale.Itwasfortunatethatthecorrugatedsteelductsaroundthetendonswerediscontinuousthroughthejointswhichallowedtheradartodetectthetendonsandvoids.Theproblem,however,wasstillhighlycomplexduetothehighdensityofothersteelelementswhichcouldinterferewiththeradarsi
30、gnalsandthefactthattheareaofinterestwasatmost102mmwideandembeddedbetween150mmand800mmdeepinthickconcreteslabs.Trialradarinvestigations.Threecompanieswereinvitedtovisitthebridgeandconductatrialinvestigation.Onecompanydecidednottoproceed.Theremainingtwoweregiven2weekstomobilize,testandreport.Theirresu
31、ltswerethencomparedwithphysicalexplorations.Tomakethecomparisons,observationholesweredrilledverticallydownwardsintotheductsataselectionof10locationswhichincludedseveralwherevoidswerepredictedandseveralwheretheductswerepredictedtobefullygrouted.A25-mmdiameterholewasrequiredinordertofacilitateuseofthe
32、chosenhoroscope.TheresultsfromtheUniversityofEdinburghyieldedanaccuracyofaround60%.Mainradarsurvey,horoscopeverificationofvoids.Havingcompletedaradarsurveyofthetotalstructure,abaroscopicwasthenusedtoinvestigateallpredictedvoidsandinmorethan60%ofcasesthisgaveaclearconfirmationoftheradarfindings.Insev
33、eralothercasessomeevidenceofhoneycombingintheinsitestitchconcreteabovetheductwasfound.Whenviewingvoidsthroughthebaroscopic,however,itprovedimpossibletodeterminetheiractualsizeorhowfartheyextendedalongthetendonductsalthoughtheyonlyappearedtooccupylessthanthetop25%oftheductdiameter.Mostofthesevoids,in
34、fact,weresmallerthanthediameteroftheflexiblebaroscopicbeingused(approximately9mm)andwereseenbetweenthehorizontaltopsurfaceofthegroutandthecurvedupperlimitoftheduct.Inaveryfewcasesthetopsofthepre-stressingstrandswerevisibleabovethegroutbutnosignofanytrappedwaterwasseen.Itwasnotpossible,usingthebarosc
35、opic,toseewhetherthosecableswerecorroded.DigitalradartestingThetestmethodinvolvedexcitingthejointsusingradiofrequencyradarantenna:1GHz,900MHzand500MHz.Thehighestfrequencygivesthehighestresolutionbuthasshallowdepthpenetrationintheconcrete.Thelowestfrequencygivesthegreatestdepthpenetrationbutyieldslow
36、erresolution.ThedatacollectedontheradarsweepswererecordedonaGSSISIRSystem10.Thissysteminvolvesradarpulsingandrecording.Thedatafromtheantennaistransformedfromananaloguesignaltoadigitalsignalusinga16-bitanaloguedigitalconvertergivingaveryhighresolutionforsubsequentdataprocessing.Thedataisdisplayedonsi
37、teonahigh-resolutioncolormonitor.Followingvisualinspectionitisthenstoreddigitallyona2.3-gigabytetapeforsubsequentanalysisandsignalprocessing.Thetapefirstofallrecordsatheader,notingthedigitalradarsettingstogetherwiththetracenumberpriortorecordingtheactualdata.Whenthedataisplayedback,oneisabletoclearl
38、yidentifyalltherelevantsettingsmakingforaccurateandreliabledatareproduction.Atparticularlocationsalongthetraces,thetracewasmarkedusingamarkerswitchontherecordingunitortheantenna.AllthedigitalrecordsweresubsequentlydownloadedattheUniversitysNDTlaboratoryontoamicro-computer.(Therawdatapriortoprocessin
39、gconsumed35megabytesofdigitaldata.)Post-processingwasundertakenusingsophisticatedsignalprocessingsoftware.Techniquesavailablefortheanalysisincludechangingthecolortransformandchangingthescalesfromlineartoaskeweddistributioninordertohighlight突出Certainfeatures.Also,thecolortransformscouldbechangedtohig
40、hlightphasechanges.Inadditiontothesecolortransformfacilities,sophisticatedhorizontalandverticalfilteringproceduresareavailable.Usingalargescreenmonitoritispossibletodisplayinsplitscreenstherawdataandthetransformedprocesseddata.Thusoneisabletogetanaccurateindicationoftheprocessingwhichhastakenplace.T
41、hecomputerscreendisplaysthetimedomaincalibrationsofthereflectedsignalsontheverticalaxis.Afurtherfacilityofthesoftwarewastheabilitytodisplaytheindividualradarpulsesastimedomainwiggleplots.Thiswasaparticularlyvaluablefeaturewhenlookingatindividualrecordsinthevicinityofthetendons.Interpretationoffindin
42、gsAfullanalysisoffindingsisgivenelsewhere,Essentiallythedigitizedradarplotsweretransformedtocolorlinescansandwheredoublephaseshiftswereidentifiedinthejoints,thenvoidingwasdiagnosed.Conclusions1. AnoutlineofthebridgeresearchplatforminEuropeisgiven.2. TheuseofimpulseradarhascontributedconsiderablytothelevelofconfidenceintheassessmentoftheBesseso,th,BamRailBridge.3. Theradarinvestigationsrevealedextensivevoidingwithinthepost-tensionedcableducts.However,nosignofcorrosiononthestressingwireshadbeenfoundexceptfortheveryfirstinvestigation.
