海洋结构翻译毕业设计翻译稿.docx

海洋结构翻译毕业设计翻译稿.docx

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海洋结构翻译毕业设计翻译稿

英语翻译原文：

MarineStructures

Corrosionratemeasurementsinsteelsheetpilewallsinamarineenvironment

Abstract

Corrosionofsteelstructuresinthemarineenvironmentisamajorproblem.Thedeteriorationofthiskindofstructuresiscostlyanddifficulttopredictbothwhendesigningnewstructuresandwhenestimatingtheremainingservicelifetimeforexistingstructures.TheaimofthisinvestigationwastofindindicativevaluesforthecorrosionrateofsteelsheetpilesontheSwedishwestcoast.Suchcorrosionrates（mm/year）canbeusedbothwhendesigningnewstructuresbyoversizingthesteelthicknessandwhenestimatingthebearingcapacityofexistingsheetpilestructures.EarlierinvestigationsonthecorrosionratesalongtheSwedisheastcoast-withsalinityfromabout0.2%to0.8%-arestillusedtodayasguidelinesforthecorrosionrateofallsteelstructuresintheSwedishmaritimeenvironmenteventhoughthesalinityonthewestcoastcanbeashighas3.0%.

SteelsheetpilewharfslocatedintheportofHalmstadontheSwedishwestcoastwereinspectedbyultrasonicmeasurements.Threewharfstructureswithatotallengthofabout700mwereinspected.Noneoftheinspectedwharfshadorhavehadcathodicprotection.Thethicknessmeasurementsofthesteelsheetpilestructureswereultrasonicbydivers.

Theageofthethreeinspectedsheetpilestructuresrangedfrom36to51years.Thedimensionsoftheoriginalsheetpilesectionsareknown.Oneofthequaystructuresislocatedalongariver.Thesalinityatallwharfsvariedfromlowvaluesatthesurfacetoapprox.2%atthebottom（alsointheriveroutflow）.

ThemeasuredaveragecorrosionrateswereinthesameorderasthedesignvaluesintheEuropeancode.However,theresultsindicateincreasedcorrosionratesabout1mbelowthemeanwatersurfaceandatthelevelofthepropellersfromtheshipsberthingthemostfrequentedoftheinspectedwharfs,3–6mbelowwatersurface.

Thetolerancesofsteelsheetthicknesses-usuallyintheorderof±6%–areoftenneglectedwheninvestigatingtheremainingthicknessinsteelsheetpiles.Asimplecalculationmodelshowsthatthesheetpilemustbealmost50yearsofagebeforeanaccurateestimationonthecorrosionratecanbemade,consideringthetolerances,ifthetrueoriginalsheetpilethicknessisnotknown.

Introduction

1.1.Background

Alargepartoftheinternationaltradeintheworldistodaytransportedatsea.Thehighervolumeoftransportedgoodsbysea,alongwithlargerfreightvessels,setincreaseddemandsonthequaysandferryberthsinourharbors.Sincetheloadsonthequaydecksincreasewithincreasedhandlingofgoodsandthedeteriorationinformofcorrosionreducesthebearingcapacityofthesheetpilestructure,thiscanleadtoacollapse.Fig.1showssometypicalquaysinindustrialharbors.

ManyofthequaysinSwedishharborshavereachedanageof60-70yearsandhave–accordingtotheoriginaldesigncriteriabasedonassumedcorrosionrates-reachedtheirdesignlifetime.Eventhoughmostofthesequaysandwharfsareactuallystillingoodconditionthereisaneedforinspectionsandpredictionsofremaininglifetimeforthesestructuresinordertoplanforrenovationsandthedesignofnewquays.

Theservicelifetimeofnewsheetpilestructureisusuallyfulfilledbyoversizingthesteelthicknessinthesheetprofile.Knowledgeaboutthecorrosionrateisalsoimportantwhenverifyingtheremainingbearingcapacityofexistingstructures,andestimatingtheremainingservicelifetimeac-cordingtobearingcapacity.Whenoversizingthestructure,acertaincorrosionrate（mm/year）isassumed.Thecorrosionisalsoassumedtobeevenalloverthesurfaceandpitcorrosionorothertypesofunevencorrosionarenotaccountedfor.Inpracticethecorrosionrateisalsoassumedtobealinearfunctionoftimebymostengineers.However,areportfromaEuropeanresearchproject[1]concludesthatthecorrosionratedecreaseswithtime.Thevaluesoncorrosionratesinthisreportarealsogiveninreference[2]andareusedbypracticingengineersinEuropetodaywhendesigningnewsteelstructures.Accordingtothisreport,thecorrosionrateneedstobetreatedstatistically.Itisprobablethatadecreasingcorrosionratewillbefoundiftheprotectivelayersofcorrosionproductsformedarenotdamagedoreroded[3].

Onewaytoestimatethecorrosionrateatacertainsiteistoperformmeasurementsonremaininggoodsthicknessonexistingstructures.Withknowledgeabouttheoriginalsheetpiledimensionsandtheyearofinstallation,itisthenpossibletoestimatetheaveragecorrosionrate.Havingknowledgeabouttheaveragecorrosionrateinindividualharborsgivesbotheconomicandenvironmentalgainsasthiskindofstructurescanthenbeoptimizedbasedontheactualrateoflossofmaterials.

Wheninvestigatingexistingsteelsheetstructures,oneusuallymeasurestheuniformcorrosionrateoveracertainareaofthestructure.Thisis,however,asimplificationofhowthecorrosionprocesstakesplace,sincethereisalsooftenpitcorrosion,whichisconcentratedtosmallareas.Pitcorrosioncangiveverymisleadingresultswhenmeasuringthesteelthicknesswiththecommonlyusedultrasonicgauges.Itisalsocommonlyfoundthatthemostseverecorrosioninsheetpilestructuresappearsinthesplashzone,whilemuchlowercorrosionratesarefoundacoupleofmetersbelowmeanwaterlevel.Thiscouldindicatethepresenceofacceleratedlowwatercorrosion（ALWC）asdescribedinreferences[4]andin[5]amongothers.NoobvioussignsofthepresenceofALWChavehoweverbeenfoundintheinvestigationpresentedinthispaper.Theabovefactorscomplicatetheestimationofthestatusofharborstructures.

1.2.Principlesofdesignofasheetpilequay

Whendesigninganewsheetpilequaythereareseveralaspectstoconsider.Thegeotechnicalconditionsareforexampleofimportanceforthefinaloperationofthestructure.Sometimesitisnecessarytoreplacenaturalweaksoilsbehindthequaywallwithcoarserfillingmaterialwithhigherbearingcapacity.Twootherdesigncriteriaaretheprescribedgroundloadfromtrucksandmobilecranesonthequaydeckbehindthesheetpilewall（cf.Fig.1）,andtheprescribedservicelifetimeofthequay.

Oneofthemostcommonquaystructurestodayistheback-anchoredsteelsheetwallasshowninFig.2.Thewallisback-anchoredeitherinbedrockorinanchorplatesinthebackfillingbehindthewall.Thematerialusedinthetierodsissteelandtheanchorplatesareusuallyprecastconcreteslabsorsteelsheetpiles.Thetierodsareprotectedagainstcorrosion,e.g.,byabitumenlining.

ThemostcommonlyusedsheetpilesectionsinharborconstructionsareZ-andU-profiles（Fig.3）.Thesheetpilesaredeliveredinsteelgradeswithminimumyieldstrengthbetween240and460MPa.Thethicknessonstandardprofilesvariesbetween6and20mmintheflangesandbetween8and16mmintheweb.Maximumstandardrollinglengthsdependsontheprofiletypechosenandvariesbetween16and33m.

Themostsensitivesection（withrespecttothebendingmomentcapacity）inaback-anchoredsheetpilewalloccursataboutonethirdoftheexcavationdepthfromtheseabottom,asthisiswherethehighestbendingmomentnormallyoccurs（Fig.4）.However,thelargestshearforceislocatedattheleveloftheattachmentoftherods.Becauseofthisitisimportanttodetectpotentialweaknessesintheflangesbelowthewatersurfaceandinthewebatthelocationoftheattachmentofthetierods.Ifthesheetpilewallsupportsthedirectverticalloadfromforexampleacrane,thecorrosionofthewholesectionistobeconsideredsincethisloadcasegivesrisetoadditionalcompressionstressesoverthewholesectionalarea.

Whendesigningasheetpilewallforacertainlocation,itwouldbeofinteresttobeabletoconsiderallthefactorsthatinfluencethecorrosionrate:

temperature,salinity,oxygenconcentration,biologicalgrowth,erosionetc.Thisisnotfeasible,butwecanfocusonthemostimportantfactorstooptimizeadesignforacertainlocation.

InSwedenwehaveratherlargevariationsintemperatureovertheyearandthesalinityrangesfromapprox.0.2%atthenortheastcoast,to0.8%atthesouthcoast,toaround3.0%attheuppernorth-westcoast.Thisuniquegradientinsalinity-seennowhereintheworldonthisscale-couldserveasatestgroundforstudiesofhowsalinityinfluencescorrosionrateinharbors.Itiswellknownthattemperatureandsalinity,togetherwithseveralotherphysicalandchemicalparameters,influencesthecorrosionofmildsteelinseawater,seeforexamplereference[6].However,thisstudyisbasedonlaboratorymeasurementsanddoesnottakeforexamplebiologicalgrowthintoaccount;undernaturalexposureithasbeenproposedthattemperatureisthemainvariablegoverningcorrosionofmarinestructures[7].

1.3.Currentdesignvaluesoncorrosionrates

Differentvaluesoncorrosionratesonsteelinmarinestructuresareusedindifferentpartsoftheworld.Informationonrecommendedratesisinsomecasesavailableinnationalorinternationalbuildingcodes.InFig.5recommendedcorrosionratesforsteelinmarineenvironmentsaresummarizedforUSA,Australia,EuropeandSweden.

Itiswell-knownthatthecorrosiononsteelinamarineenvironmentisnotlinear,seeforexamplethemeasurementspresentedinthereportonwhichtheEurocodeisbased[1].Severalmodelsfordescribingthenon-linearityhasbeendevelopedduringtheyears;oneofthemorerefinedmodelsisthatpresentedbyMelchers[7].Thenon-linearbehav