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毕业设计英文翻译学院：建筑工程学院专业：土木工程学生姓名:学号:设计题目：近期美国在钢结构和钢筋混凝土结构研究和设计方面的发展指导教师:专业负责人：起迄日期:设计地点:发任务书日期:年月日RecentResearchandDesignDevelopmentsinSteelandCompositeSteel-concreteStructuresinUSAThepaperwillconcludewithalooktowardthefutureofstructuralsteelresearch.1.ResearchonsteelbridgesTheAmericanAssociationofStateTransportationandHighwayOfficials(AASTHO)istheauthoritythatpromulgatesdesignstandardsforbridgesintheUS.In1994ithasissuedanewdesignspecificationwhichisaLimitStatesDesignstandardthatisbasedontheprinciplesofreliabilitytheory.Agreatdealofworkwentintothedevelopmentofthiscodeinthepastdecade,especiallyoncalibrationandontheprobabilisticevaluationofthepreviousspecification.Thecodeisnowbeingimplementedinthedesignoffice,togetherwiththeintroductionoftheSystemeInternationaleunits.Manyquestionsremainopenaboutthenewmethodofdesign,andtherearemanynewprojectsthatdealwiththereliabilitystudiesofthebridgeasasystem.Onesuchcurrentprojectisastudytodevelopprobabilisticmodels,loadfactors,andrationalload-combinationrulesforthecombinedeffectsoflive-loadandwind;live-loadandearthquake;live-load,windandshipcollision;andshipcollision,wind,andscour.Therearealsomanyfieldmeasurementsofbridgebehavior,usingmoderntoolsofinspectionandmonitoringsuchasacousticemissiontechniquesandothermeansofnon-destructiveevaluation.Suchfieldworknecessitatesparallelstudiesinthelaboratory,andtheevolutionofevermoresophisticatedhigh-technologydatatransmissionmethods.Americahasanagingsteelbridgepopulationandmanyproblemsarisefromfatigueandcorrosion.Fatiguestudiesonfull-scalecomponentsoftheWilliamsburgBridgeinNewYorkhaverecentlybeencompletedatLehighUniversity.AprobabilisticAASTHObridgeevaluationregulationhasbeenineffectsince1989,anditisemployedtoassessthefutureusefullifeofstructuresusingrationalmethodsthatincludefieldobservationandmeasurementtogetherwithprobabilisticanalysis.Suchanactivityalsofostersadditionalresearchbecausemanyissuesarestillunresolved.Onesuchareaisthestudyoftheshakedownofshearconnectorsincompositebridges.ThisworkhasbeenrecentlycompletedattheUniversityofMissouri.Inadditiontofatigueandcorrosion,themajordangertobridgesisthepossibilityofearthquakeinduceddamage.Thisalsohasspawnedmanyresearchprojectsontherepairandretrofitofsteelsuperstructuresandthesupportingconcretepiers.Manybridgesinthecountryarebeingstrengthenedforearthquakeresistance.Oneareathatisreceivingmuchresearchattentionisthestrengtheningofconcretepiersbyjacketingthembysheetsofhigh-performancereinforcedplastic.Thepreviouslydescribedresearchdealsmainlywiththebehaviorofexistingstructuresandthedesignofnewbridges.However,thereisalsoavigorousactivityonnovelbridgesystems.Thisresearchiscenteredontheapplicationofhigh-performancesteelsforthedesignofinnovativeplateandbox-girderbridges,suchascorrugatedwebs,combinationsofopenandclosedshapes,andlongerspansfortrussbridges.Itshouldbementionedherethat,inadditiontoworkonsteelbridges,thereisalsoveryactiveresearchgoingoninthestudyofthebehaviorofprestressedconcretegirdersmadefromveryhighstrengthconcrete.Theperformanceanddesignofsmallerbridgesusingpultrudedhigh-performanceplasticcompositemembersisalsobeingstudiedextensivelyatpresent.Newcontinuousbridgesystemswithsteelconcretecompositesegmentsinboththepositivemomentandthenegativemomentregionsarebeingconsidered.Severalresearchershavedevelopedstrongcapabilitiestomodelthethree-dimensionalnon-linearbehaviorofindividualplategirders,andmanystudiesarebeingperformedonthebucklingandpost-bucklingcharacteristicsofsuchstructures.Companionexperimentalstudiesarealsomade,especiallyonmembersbuiltfromhigh-performancesteels.Afull-scalebridgeofsuchsteelhasbeendesigned,andwillsoonbeconstructedandthentestedundertrafficloading.Researcheffortsarealsounderwayonthestudyofthefatigueoflargeexpansionjointelementsandonthefatigueofhighwaysignstructures.Thefinalsubjecttobementionedistheresurgenceofstudiesofcompositesteelconcretehorizontallycurvedsteelgirderbridges.AjustcompletedprojectattheUniversityofMinnesotamonitoredthestressesandthedeflectionsinaskewedandcurvedbridgeduringallphasesofconstruction,startingfromthefabricationyardtothecompletedbridge.~Excellentcorrelationwasfoundtoexistbetweenthemeasuredstressesanddeformationsandthecalculatedvalues.Thestressesanddeflectionsduringconstructionwerefoundtoberelativelysmall,thatis,theconstructionprocessdidnotcauseseveretraumatothesystem.Thebridgehasnowbeentestedunderserviceloading,usingfullyloadedgraveltrucks,fortwoyears,anditwillcontinuetobestudiedforfurtheryearstomeasurechangesinperformanceunderserviceovertime.AmajortestingprojectisbeingconductedattheFederalHighwayAdministrationlaboratoryinWashington,DC,whereahalf-scalecurvedcompositegirderbridgeiscurrentlybeingtestedtodetermineitslimitstates.Thetest-bridgewasdesignedtoactasitsowntest-frame,wherevariousportionscanbereplacedaftertesting.Multipleflexuretests,sheartests,andtestsundercombinedbendingandshear,arethusperformedwithrealisticend-conditionsandrestraints.Theexperimentsarealsomodeledbyfiniteelementanalysistocheckconformancebetweenrealityandprediction.Fina