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学院建筑工程学院

专业班级土木工程2012级3班

学生姓名张乐

学号2012442844

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RecentResearchandDesignDevelopmentsinSteelandCompositeSteel-concreteStructuresinUSA

Thepaperwillconcludewithalooktowardthefutureofstructuralsteelresearch.

1.Researchonsteelbridges

TheAmericanAssociationofStateTransportationandHighwayOfficials（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.Oneareathatisreceivingmuchresearchattentionisthestrengtheningofconcretepiersby"

jacketing"

thembysheetsofhigh-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.Finallydesignstandardswillbeevolvedfromtheknowledgegained.ThislastprojectisthelargestbridgeresearchprojectintheUSAatthepresenttime.

Fromthediscussionaboveitcanbeseenthateventhoughthereisnolargeexpansionofthenation'

shighwayandrailroadsystem,thereisextensiveworkgoingoninbridgeresearch.Themajorchallengefacingboththeresearcherandthetransportationengineeristhemaintenanceofahealthybutagingsystem,seeingtoitsgradualreplacementwhilekeepingitsafeandserviceable.

2.Researchonsteelmembersandframes

Therearemanyresearchstudiesonthestrengthandbehaviorofsteelbuildingstructures.Themostimportantofthesehavetodowiththebehavioranddesignofsteelstructuresundersevereseismicevents.Thistopicwillbediscussedlaterinthispaper.Themostsignificanttrendsofthenon-seismicresearcharethefollowing:

"

Advanced"

methodsofstructuralanalysisanddesignareactivelystudiedatmanyUniversities,notablyatCornell,Purdue,Stanford,andGeorgiaTechUniversities.Suchanalysismethodsaremeanttodeterminetheload-deformationbehaviorofframesuptoandbeyondfailure,includinginelasticbehavior,forceredistribution,plastichingeformation,second-ordereffectsandframeinstability.Whenthesemethodsarefullyoperational,thestructurewillnothavetoundergoamembercheck,becausethefiniteelementanalysisoftheframeautomaticallyperformsthisjob.Inadditiontotheresearchonthebestapproachestodothisadvancedanalysis,therearealsomanystudiesonsimplificationsthatcanbeeasilyutilizedinthedesignofficewhilestillmaintainingtheadvantagesofamorecomplexanalysis.Theadvancedanalysismethodiswelldevelopedforin-planebehavior,butmuchworkisyettobedoneonthecaseswherebi-axialbendingorlateraltorsionalbucklingmustbeconsidered.Somesuccesseshavebeenachieved,buttheresearchisfarfromcomplete.

Anotheraspectoftheframebehaviorworkisthestudyoftheframeswithsemirigidjoints.TheAmericanInstituteofSteelConstruction（AISC）haspublisheddesignmethodsforofficeuse.Currentresearchisconcentratingonthebehaviorofsuchstructuresunderseismicloading.Itappearsthatitispossibletousesuchframesinsomeseismicsituations,thatis,framesunderabout8to10storiesinheightundermoderateearthquakeloads.Thefutureofstructureswithsemi-rigidframeslooksverypromising,mainlybecauseoftheeffortsofresearcherssuchasLeonatGeorgiaTechUniversity,andmanyothers.

Researchonmemberbehaviorisconcernedwithstudyingthebucklingandpostbucklingbehaviorofcompactangleandwide-flangebeammembersbyadvancedcommercialfiniteelementprograms.Suchresearchisgoingbacktoexaminetheassumptionsmadeinthe1950sand1960swhentheplasticdesigncompactnessandbracingrequirementswerefirstformulatedonasemi-empiricalbasis.Thenon-linearfiniteelementcomputationspermitthe"

re-testing"

oftheoldexperimentsandtheperformingofnewcomputerexperimentstostudynewtypesofmembersandnewtypesofsteels.WhiteofGeorgiaTechisoneofthepioneersinthiswork.SomecurrentresearchattheUSmilitaryAcademyandattheUniversityofMinnesotabyEarlsisdiscussedlaterinthisreport.Thesignificanceofthistypeofresearchisthatthephenomenaofextremeyieldinganddistortioncanbeefficientlyexaminedinparameterstudiesperformedonthecomputer.Thecomputerresultscanbeverifiedwitholdexperiments,orasmallnumberofnewexperiments.Thesestudiesshowagoodprospectfornewinsightsintooldproblemsthatheretoforewereneverfullysolved.

3.Researchoncold-formedsteelstructures

Nexttoseismicwork,themostactivepartofresearchintheUSisoncold-formedsteelstructures.Thereasonforthisisthatthesupportingindustryisexpanding,especial