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原文secret.docx
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原文secret
China-JapanJointSeminaronSteelandCompositeBridges
DesignofSteelPlate-TrussCompositeGirderof
CableStayedMinpuBridgeII
J.Peng,W.L.Deng,L.Zhou,Y.C.Lu,M.Zhu
ShanghaiUrbanConstructionDesign&ResearchInstitute,Shanghai200011,China
Abstract:
MinpuBridgeIIisasuperlargebridgewiththeintegrateddoubledecksforhighwayandrailwaytraffic.Themainpartiscable-stayedthroughasinglepylonanddoublecablesectors,withthespanlargestinChina.Describedherebyishowtoselectthemaingirderofthemainspancable-stayedbridgefrommultipleoptions.Thesteelplate-trusscompositegirderisfinallyadopted,whichisstructurallyreliable,withappropriatefunctionsandsimpleconstruction.
Keywords:
highway-railwaydouble-deckbridge;cable-stayedbridge;steelplate-trusscompositegirder;bridgedesign
1.DESCRIPTIONOFWORKS
AcrosstheHuangpuRiverinShanghaiattheupperstreamofMinhangandFengxian,and1.7kmfromFengpuBridgedown,MinpuBridgeIIisasuperlargebridgewithintegrateddoubledecksforhighwayandrailwaytraffic.Themainpartisformedbyadouble-deckcable-stayedbridgewithasinglepylonanddoublecablesectors,andthemainspanis251mwide.Theupperdeckis18minwidth,usedforatwo-wayfourlanehighway(ClassII);thelowerdeckisfortwolightrails,i.e.ShanghaiRailTransitLine5inMin-FengSection,withtheminimumfunctionalwidthof10m.
Figure1Thelayerofthemainbridge
2.COMPARISONOFOPTIONSFORMAINGIRDER
Withonlyafewexceptions,thelargespandouble-deckbridgesbuiltusuallyusethesteeltrussgirderforthemaingirder,whichisnodoubtmoreappropriateintermsofstructuralperformanceandconstructionapplicability.Theeffectofthetrussedgirderisdifferent,subjecttothearrangementofmembers,soitiscriticaltoselectanoptimaldesignadaptabletothetypeofbridge.InthedesignofthemaintrussedgirderonthemainspanofMinpuBridgeII,comparisonsandstudiesarecarriedoutonthreeaspects,i.e.theshapeoftruss,thecrossectionofthetrussandthedeck.
2.1ShapeofTruss
Theshapeoftrusscurrentlyprevailingismainlyofthepurewarrentruss(triangulartruss),warrentrussandPratttruss(N-formedtruss),thedifferenceofwhichliesonlyinthearrangementofthewebmemberswhilenogreatdifferenceisfoundinthestructuralperformance,allapplicabletechnically.Withmoresuccinctlinesandcontour,thetriangularandN-formedtrussesarewidelyusedonmoderntrussedgirderbridges.Besides,thenumberofmembersconnectedtothetrussnodesisminimum,i.e.only4,whichisbeneficialtosimplifythefabricationoftrusses.Forthetriangulartruss,whichiswidelyusedinatrussofarectangularsection,itismorecomplicatedtoprovidethetransverseknee-braceforlackoftheverticalpost.Ontheother
hand,theshapeoftrussshallalsomatchthecablearrangementofthecable-stayedbridgetokeepaproperrelationshipwiththeforcethereon.ForanN-formedtrusstotheharp-shapedcablesector,thebestmatchedshapeisthatthediagonalwebandcablesareclosetoastraightline.Inthatcase,thefabricationofnodesisalmoststandardilikeOresundBridgeinSweden.Itmustbequitecareful,however,tousethistypeasthelengthbetweenthetrussesisgreaterthannormal,causinggreaterforceontheweb.ThereisnosubstantialdifferenceintheshapeandthecomplexityatthenodebetweenthetriangulartrussandthenormalN-formedtrusswiththefan-shapedorharp-shapedcablesector,butthetriangulartrussisatrendofdevelopmentofthesteeltruss.
2.2TheCrossSectionofTruss
Thecrosssectionofthetrussismainlyarrangedintwoshapes,rectangularandinvertedtrapezoid,andtheformeristhemostpopularintrussbridges,withnoexceptionofthedouble-decktype.Innormalcases,theupperdeckforthehighwayinthedouble-deckbridgeisusuallywiderthanthelowerdeckfortherailwayorlightrailsoitismostappropriatetoadopttheshapeofaninvertedtrapezoidonlyintermsofmatchingthecrossarrangementofthebridgeandeconomicbenefit.However,thecompositionofthetrusssectionandthetypeofbridge,theadvantageanddisadvantagearemoreapparent.Forarchandsuspensionbridges,theinvertedtrapezoidalcrosssectionismostsuitableasthereisnohorizontalcomponentofforcealongthebridgeduetotheverticalhangingmembersandasnoextracomplexitymayariseintheforcesustainedandthestructure.Iftherectangularcrosssectionisadoptedforcable-stayedbridge,thecablesandthemaintrussaregenerallyonthesameplane,andthehorizontalcomponentofthecableforceistransferreddirectlytothemainchordmembersotheforceisclearanddefiniteandthestructureofcable-trussconnectionisnormal.Whilefotheinvertedtrapezoidalsection,theextrasecondarytrussisrequiredtotransferthecableforceasthecableandthemaintrussisnotonthesameverticalplane,where
itisdifficulttohandlethehorizontalcomponentofcableforce.BeneficialattemptshavebeenmadeinthisaspectonOresundBridgeandWuhuYangtzeBridge.Itshowsthroughcomparisonsthattheeconomicadvantageoftheinvertedtrapezoidsectionisweakenedasthematerialfortheextrapowerfulsecondarytrussalmostoffsetsthequantityofmaterialforthereducedlowerdeck,andthecostofitsfabricationishigherduetothestructuralcomplexityofthecable-trussconnection.Soitisappropriatetousethetrusswiththerectangularsectionforthecable-stayedbridge.
Table2.1AComparisonofTrussSections
Rectangular
InvertedTrapezoid
Schematics
Advantages
1.Adaptabletoanytypeoftruss,simpleinhandlingthenode,bearingtheforcedirectanddefinite.
1.Thelowerdeckbeinglesswidethantheupperoneenablesamorecompactstructurallayoutandthelowertransbeambearslessforce.
Disadvantages
1.Thelowerdeckbeinglesswidethantheupperonemeansthestructurallayoutislesseconomicandthelowertransbeambearsgreaterforce.
1.FortrussesofPrattorWarrentype,itiseasiertohandlethenodeasthesubdiagonalrodandtheverticalwebareonthesameverticalplane,butitisdifficultincaseofthepureWarranttruss;
2.There’sforcebetweenthetrusses.
ConditionsApplicable
1.Itisstructurallysimpleforanytypeofbridge,bearingtheforceclear,definiteandreliable.
1.Forarchandsuspensionbridges,itisstructurallysimple,bearingforcemoredefinite,butforcable-stayedbridges,itismorecomplicatedasextrasecondarytrussesarerequiredtobearthehorizontalcomponentforce.
2.3TheDeck
(1)UpperDeck
Theupperdeckstructureisoftwotypes,i.e.theorthotropicsteelplateandtheconcreteslacorrespondingtotwokindsofconnectionwiththetruss,i.e.thesystemoftheorthotropicsteelplateandthetrusscompositionandthesystemoftheconcreteslabandtrusscomposition.Theconcretedeckmayalsobesubdividedintotwoforms,theconcretedeckslabisonlyconnectedwiththeupperchord(Form1)andtheconcretedeckslabisconnectedwithboththeupperchordandthetransbeam(Form2),whoseadvantagesanddisadvantagesareshowninthefollowingTable2.2
Table2.2AComparisonofUpperDeckForms
Orthotropicsteelplate
Concreteslab(Form1)
Concreteslab(Form2)
Featuresofforceborne
Forceisbornebythewholeplate
Forceisbornebythewholeslab
Forceisbornebythewholeslab
Advantages
1.Theplateandtrussareofthesamematerialwithoutthematerialdifferenceinconnection;
2.withlessself-weight
1.Forceonslab-trusscompositionisclearanddefinite;
2.Theupperstructurecostless;
3.Themaingirderisofhigherrigidityandlowerflexibility
1.Atwo-waydeck,andthedeckthicknessmaybereduced;
2.Thecostislowerforthesuperstructure;
3.themaingirderisofhighrigidityandlowerflexibility,especiallywiththestructuralweightrigidityincreased,thenon-lineardeformationofdynamicloadsisreduced.
Disadvantages
1.Thesuperstructurecostsmoreasmoresteelisrequired;
2.Pavingasphaltonthesteeldeck
requireshighertechniquesothecostishigher.
1.Greaterselfweightrequiresmoreanchorsandspanstokeepbalance;
2.Theinternalforceisredistributedduetocontractionandcreepofconcrete;
3.Requiringmorestepsofconstructionprocedure
1.Greaterselfweightrequiresmoreanchorsandspanstokeepbalance;
2.Theinternalforceisredistributedduetocontractionandcreepofconcrete;
3.Theforceontheslabismorecomplicated.
Examples
CaiyuanbaBridge
OresundBridge
WuhuYangtzeBridge
(2)LowerDeck
Table2.3AComparisionofLowerDeckForms
OpenDeck
ConcreteRailGirder
Orthotropicsteelboxgirder
Orthotropicsteelplate
Featuresofforceborne
Smallbeamsareprovideunderthesleeperswhichonlybearthelocalforce.
Therailbeamisplacedontheuppertransbeamfixedorconnectedwiththebearing
Forceisbornebythewholegirder
Forcemaybebornebythewholeplateoronlybysomelocalplaces.
Advantages
1.Structurallysimple;
2.Withsmallerselfweight;
3.Forceborneisclearanddefinite
1.Therigidityofthemaingirderwillbeincreasedifitbearstheforcejointly.
1.Withsmallerselfweight;
2.Thetrussrigidityverticalandhorizontalisincreased
1.Theinternalrigidityunderthetrussisincreased.
Disadvantages
1.Railsgenerategreaternoiseduringoperation;
2.Difficultinmaintenance;
3.Difficultinhandlingthestraycurrentontherail.
1.Withgreaterselfweightduringoperation;
2.Thelowertransbeamisundergreaterandmorecomplicateforce,i.e.bending,shearandtwisting;
3.Spe
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