英文文献欧洲桥梁研究.docx
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英文文献欧洲桥梁研究
BridgeresearchinEurope
AbriefoutlineisgivenofthedevelopmentoftheEuropeanUnion,togetherwiththeresearchplatforminEurope.Thespecialcaseofpost-tensionedbridgesintheUKisdiscussed.InordertoillustratethetypeofEuropeanresearchbeingundertaken,anexampleisgivenfromtheUniversityofEdinburghportfolio:
relatingtotheidentificationofvoidsinpost-tensionedconcretebridgesusingdigitalimpulseradar.
Introduction
Thechallengeinanyresearcharenaistoharnessthefindingsofdifferentresearchgroupstoidentifyacoherentmassofdata,whichenablesresearchandpracticetobebetterfocused.AparticularchallengeexistswithrespecttoEuropewherelanguagebarriersareinevitablyverysignificant.TheEuropeanCommunitywasformedinthe1960sbaseduponapoliticalwillwithincontinentalEuropetoavoidtheEuropeancivilwars,whichdevelopedintoWorldWar2from1939to1945.ThestrongpoliticalmotivationformedtheoriginalcommunityofwhichBritainwasnotamember.ManyofthecontinentalcountriessawBritain’sinterestasbeingpurelyeconomic.The1970ssawBritainjoiningwhatwasthentheEuropeanEconomicCommunity(EEC)andthe1990shasseenthewideningofthecommunitytoaEuropeanUnion,EU,withcertainpoliticalgoalstogetherwiththeobjectiveofacommonEuropeancurrency.
Notwithstandingthesefinancialandpoliticaldevelopments,civilengineeringandbridgeengineeringinparticularhavefoundgreatdifficultyinforminganykindofcommonthread.IndeedtheeducationalsystemsforUniversitytrainingarequitedifferentbetweenBritainandtheEuropeancontinentalcountries.TheformationoftheEUfundingschemes—e.g.Socrates,BriteEuramandotherprogramshavehelpedsignificantly.TheSocratesschemeisbasedupontheexchangeofstudentsbetweenUniversitiesindifferentmemberstates.TheBriteEuramschemehasinvolvedtechnicalresearchgrantsgiventoconsortiaofacademicsandindustrialpartnerswithinanumberofthestates—aBriteEurambidwouldnormallybeledbyanindustrialist.
Intermsofdisseminationofknowledge,twoquitedifferentstrandsappeartohaveemerged.TheUKandtheUSAhaveconcentratedprimarilyupondisseminatingbasicresearchinrefereedjournalpublications:
ASCE,ICEandotherjournals.WhereasthecontinentalEuropeanshavefrequentlydisseminatedbasicresearchatconferenceswherethecirculationoftheproceedingsisrestricted.
Additionally,languagebarriershaveprovedtobeverydifficulttobreakdown.IncountrieswhereEnglishisastrongsecondlanguagetherehasbeenenthusiasticparticipationininternationalconferencesbasedwithincontinentalEurope—e.g.Germany,Italy,Belgium,TheNetherlandsandSwitzerland.However,countrieswhereEnglishisnotastrongsecondlanguagehavebeenhesitantparticipants}—e.g.France.
Europeanresearch
ExamplesofresearchrelatingtobridgesinEuropecanbedividedintothreetypesofstructure:
Masonryarchbridges
Britainhasthelargeststockofmasonryarchbridges.IncertainregionsoftheUKupto60%oftheroadbridgesarehistoricstonemasonryarchbridgesoriginallyconstructedforhorsedrawntraffic.ThisislesscommoninotherpartsofEuropeasmanyofthesebridgesweredestroyedduringWorldWar2.
Concretebridges
Alargestockofconcretebridgeswasconstructedduringthe1950s,1960sand1970s.Atthetime,thesestructureswereseenasmaintenancefree.Europealsohasalargenumberofpost-tensionedconcretebridgeswithsteeltendonductspreventingradarinspection.ThisisaparticularprobleminFranceandtheUK.
Steelbridges
SteelbridgeswentoutoffashionintheUKduetotheirneedformaintenanceasperceivedinthe1960sand1970s.However,theyhavebeenusedforlongspanandrailbridges,andtheyarenowreturningtofashionformotorwaywideningschemesintheUK.
ResearchactivityinEurope
ItgivesanindicationcertainareasofexpertiseandworkbeingundertakeninEurope,butisbynomeansexhaustive.
InordertoillustratethetypeofEuropeanresearchbeingundertaken,anexampleisgivenfromtheUniversityofEdinburghportfolio.Theexamplerelatestotheidentificationofvoidsinpost-tensionedconcretebridges,usingdigitalimpulseradar.
Post-tensionedconcreterailbridgeanalysis
OveArupandPartnerscarriedoutaninspectionandassessmentofthesuperstructureofa160mlongpost-tensioned,segmentalrailwaybridgeinManchestertodetermineitsload-carryingcapacitypriortoatransferofownership,foruseintheMetrolinklightrailsystem..
Particularattentionwaspaidtotheintegrityofitspost-tensionedsteelelements.Physicalinspection,non-destructiveradartestingandotherexploratorymethodswereusedtoinvestigateforpossibleweaknessesinthebridge.
SincethesuddencollapseofYnys-y-GwasBridgeinWales,UKin1985,therehasbeenconcernaboutthelong-termintegrityofsegmental,post-tensionedconcretebridgeswhichmaybeproneto‘brittle’failurewithoutwarning.Thecorrosionprotectionofthepost-tensionedsteelcables,wheretheypassthroughjointsbetweenthesegments,hasbeenidentifiedasamajorfactoraffectingthelong-termdurabilityandconsequentstrengthofthistypeofbridge.Theidentificationofvoidsingroutedtendonductsatvulnerablepositionsisrecognizedasanimportantstepinthedetectionofsuchcorrosion.
Descriptionofbridge
Generalarrangement
Besseso’th’BarnBridgeisa160mlong,threespan,segmental,post-tensionedconcreterailwaybridgebuiltin1969.Themainspanof90mcrossesoverboththeM62motorwayandA665BurytoPrestwickRoad.Minimumheadroomis5.18mfromtheA665andtheM62isclearedbyapprox12.5m.
Thesuperstructureconsistsofacentralhollowtrapezoidalconcreteboxsection6.7mhighand4mwide.Themajorityofthesouthandcentralspansareconstructedusing1.27mlongpre-castconcretetrapezoidalboxunits,post-tensionedtogether.Thisboxsectionsupportstheinsiteconcretetransversecantileverslabsatbottomflangelevel,whichcarrytherailtracksandballast.
Thecenterandsouthspansectionsareofpost-tensionedconstruction.Thesepost-tensionedsectionshavefivetypesofpre-stressing:
1.Longitudinaltendonsingroutedductswithinthetopandbottomflanges.
2.Longitudinalinternaldrapedtendonslocatedalongsidethewebs.Thesearedeflectedatinternaldiaphragmpositionsandareencasedininsiteconcrete.
3.Longitudinalmacalloybarsinthetransversecantileverslabsinthecentralspan.
4.Verticalmacalloybarsinthe229mmwidewebstoenhanceshearcapacity.
5.Transversemacalloybarsthroughthebottomflangetosupportthetransversecantileverslabs.
Segmentalconstruction
Thepre-castsegmentalsystemofconstructionusedforthesouthandcenterspansectionswasanalternativemethodproposedbythecontractor.Currentthinkingsuggeststhatsuchaformofconstructioncanleadto‘brittle’failureoftheentirestructurewithoutwarningduetocorrosionoftendonsacrossaconstructionjoint,Theoriginaldesignconcepthadbeenforinsiteconcreteconstruction.
Inspectionandassessment
Inspection
Inspectionworkwasundertakeninanumberofphasesandwaslinkedwiththetestingrequiredforthestructure.Theinitialinspectionsrecordedanumberofvisibleproblemsincluding:
1、Defectivewaterproofingontheexposedsurfaceofthetopflange.
2、Watertrappedintheinternalspaceofthehollowboxwithdepthsupto300mm.
3、Variousdrainageproblemsatjointsandabutments.
4、Longitudinalcrackingoftheexposedsoffitofthecentralspan.
5、Longitudinalcrackingonsidesofthetopflangeofthepre-stressedsections.
6、Widespreadsaplingonsomeinsiteconcretesurfaceswithexposedrustingreinforcement.
Assessment
Thesubjectofanearlierpaper,theobjectivesoftheassessmentwere:
1、Estimatethepresentload-carryingcapacity.
2、Identifyanystructuraldeficienciesintheoriginaldesign.
3、Determinereasonsforexistingproblemsidentifiedbytheinspection.
Conclusiontotheinspectionandassessment
Followingtheinspectionandtheanalyticalassessmentonemajorelementofdoubtstillexisted.Thisconcernedtheconditionoftheembeddedpre-stressingwires,strands,cablesorbars.Forthepurposeofstructuralanalysistheseelements、hadbeenassumedtobesound.However,duetotheveryhighforcesinvolved,、arisktothestructure,causedbycorrosiontotheseprimaryelements,wasidentified.
Theinitialrecommendationswhichcompletedthefirstphaseoftheassessmentwere:
1.Carryoutdetailedmaterialtestingtodeterminetheconditionofhiddenstructuralelements,inparticular
thegroutedpost-tensionedsteelcables.
2.Conductconcretedurabilitytests.
3.Undertakerepairstodefectivewaterproofingandsurfacedefectsinconcrete.
Testingprocedures
Non-destructiveradartesting
Duringthefirstphaseinvestigationatajointbetweenpre-castdecksegmentstheobservationofavoidinapost-tensionedcableductgaverisetoseriousconcernaboutcorrosionandtheintegrityofthepre-stress.However,theextentofthisproblemwasextremelydifficulttodetermine.Thebridgecontains93jointswithanaverageof24cablespassingthrougheachjoint,i.e.therewereapprox.2200positionswhereinvestigationscouldbecarriedout.Atypicalsectionthroughsuchajointisthatthe24drapedtendonswithinthespinedidnotgiverisetoconcernbecausethesewereprotectedbyinsiteconcretepouredwithoutjointsafterthecableshadbeenstressed.
Asitwasclearlyimpracticaltoconsiderphysicallyexposingalltendon/jointintersections,radarwasusedtoinvestigatealargenumbersoftendonsandh