Zhengzhou-Yellow-River-road-cum-railway-bridge--Ch

151Stahlbau81(2012),Heft2Berichteandtheroadliveloadisthe1.3Chinahighwayloadforeachlane.2Designofthemainbridge2.1GeneralThebedoftheYellowRiverissensitivetoscourandsedimentation,sothemainchannelriverbedhasoftenvar-iedinthepast.Accordingtostatisticsandthetestdatum,thetotallengthofthemainbridgeis1680mandisdi-videdintotwosections(Fig.2):thefirstisasix-pylonsteel-concretecom-positetrussextradosedbridgewithaspanarrangementof120+5×168+120m;thesecondisacontinuoussteel-concretecompositetrusswithaspanarrangementof5×120m.ThefirstsectionspansthemainchanneloftheYellowRiver.Thetotallengthandspanarrangementsofthemain1IntroductionZhengzhouYellowRiverroad-cum-rail-waybridgecarriestheBeijing–Guang-zhoupassengerrailwayandtheZheng-zhou–Xingxianginter-cityhighwayacrosstheYellowRiver.Thetotallengthofthebridgeis9.17km.Theupperdeckaccommodatesasix-lanecarriagewaywithadesignspeedof100km/h,thelowerdeckatwin-trackrailwaywithadesignspeedof350km/h.Thisarticledescribesthedesign,globalanalysisandconstruc-tionofthemainbridge.Therailwayliveloadis0.8UICforeachtrack,ZhengzhouYellowRiverroad-cum-railwaybridge,ChinaZongyuGaoDOI:10.1002/stab.201201522ZhengzhouYellowRiverroad-cum-railwaybridgeaccommodatesboththeBeijing–GuangzhoupassengerrailwaylineandtheZhengzhou–Xinxianginter-cityhighway,whichcrosstheYellowRiveratZhengzhou,China(Fig.1).Thebridgeis9177mlongandhastwodistinctsections[1]:thefirstisasix-pyloncontinuoussteel-concretecompositetrussextradosedbridgewithaspanarrangementof120+5×168+120m;thesecondisacontinuoussteel-concretecompositetrusswithaspanarrangementof5×120m.Themainbridgehasadoubledeck,withasix-lanecarriagewayontheupperdeckandatwin-trackrailwayonthelowerdeck.Aninclinedtrussstructureisusedforthemainbridgesuperstructure.Theupperdeckisofconcrete,thelowerdeckusesorthotropicsteelso-lution.Theanalysisrevealedthatthemainbridgehasgoodrigidityandfavourableserviceconditionsforhigh-speedtrains.Themainsteeltrusswasconstructedbyincrementallaunching.Fig.1.ViewofmainbridgeFig.2.Elevationofmainbridge(units:m)1080(1stsection)600(2ndsection)152BerichteStahlbau81(2012),Heft2bridgemeettherequirementsoffloodcontrolandgiveprominencetothiskeystructure.Inordertoovercometheunfavourabletemperatureeffectsonfoundationsforsuchalongsuper-structure,thesupportedsystemadoptsrigidpylonandtrussconnectionsandissupportedonseparatepiers.Themaingirderisasteel-concretecom-positetruss.Therailwaydeckusesasteelorthotropicdeckandtheroaddeckaprefabricatedconcreteslab.Thefirstsectionisstiffenedbystaycablessothestructureisrigid;thehorizontalrotationofthetrussendisverysmallandenhancesthecomfortofthehigh-speedpassengertrains.Theconcreteroaddeckisconvenientformainte-nance.Inordertoreducethedeckwidthandsimplifytheconnectionwiththemaingirder,asteelstructurewasadoptedforthepylons.Asingle-planefansystemisusedforthestaycables.Fig.3showstheglobalrestraintsys-tem.StructuralsteelisgradeQ370qEforthemaintrusses,Q235Cfortheupperbracingsystemandauxiliarystructures.2.2SubstructureThepylonsaresupportedonboredfric-tionpiles:32cast-in-placeboredpileswithadiameterof2.0mandalengthof95.0mforeachpylon.Theconcreteforthepiershaftswasrequiredtohaveacubecompressivestrengthof40MPa.Theunderwaterconcreteforthepileswasrequiredtohaveacubecompressivestrengthof30MPa.2.3SteeltrussTheupperdeckaccommodatesasix-lanecarriageway,withatotalwidthof32.5m;thelowerdeckaccommodatesdoubletrackswithatotalwidthof15m;thewidthdifferencebetweenroaddeckandrailwaydeckisthere-fore17.5m.Severalproposalswerestudied(Table1).Thefirstproposaladoptedthetraditionalconfiguration(Fig.2)withatrusswidthof17mandcantileverlengthof7.75m;thestruc-tureiscomplex,expensiveandpoorforthelandscape[2].Thesecondproposaladopteda24mtrusswidthandre-ducedthecantileverlengthto4.25m;thequantitiesofsteelplateincreasedbyabout3.5t/mandthisproposalwasthereforelesseconomic.Proposal3adoptedathree-planetrusswithoneinnerverticaltrussplaneandtwoout-sideinclinedtrussplanes.Afteradetailedcomparisonandbrainstormingsession,proposal3wasapprovedbytheexpertgroupandtheclient.Theroaddecktransversespanishalvedbythemiddletrussplane,thecantileverlengthoftheroaddeckis4.25mandissupportedbysteelstruts.Themaintrusshasatriangulartrusswithadepthof14mandbaylengthof12m.Thetrussis24mwidebetweenupperchordcentre-linesand17mbetweenlowerchordcentre-lines.Theinnertrussplaneisverticalandthesidetrussplanesareinclinedat14.036°.Eachsidetrusschordmemberisaparallelograminsection(Fig.4).Thetopchordmemberis1200mmdeepand940mmwide,andplatethicknessesrangefrom20to50mm.Thebottomchordmemberis1400mmdeepand940mmwide,andplatethicknessesrangefrom16to50mm.Fig.3.TheglobalrestraintsystemTable1.Comparisonofthethreetrusscross-sectionproposalsProposal123Cross-sectionRailwaydeckwidth(m)172417Steelweight(t/m)25.827.223.7Fig.4.Photoofcross-sectionofbottomchord153Stahlbau81(2012),Heft2Berichte2.4RoaddeckInordertopromoteanefficientcon-creteroaddeckandenhancetheglobalrigidity,theprecastconcreteslabdeckisconnectedtothetopchordofthemaintrusswithheadedstudsandinsituconcrete;thetransversestrutispositionedatthepaneljoint(Fig.5).P