预应力混凝土桥梁顶推法施工

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1、TheIncrementalLaunchingMethodInPrestressedConcreteBridgeConstruction——选自：《VSLINTERNATIONALLTD.Berne/switzerland》1.Introduction1.1.GeneralFig.1:PrincipleofconstructionTheincrementallaunchingmethodisoneofthehighlymechanizederectionmethodsusedinbridgeconstruction.Themethodconsistsofmanufa

2、cturingthesuperstructureofabridgebysectionsinaprefabricationareabehindoneoftheabutments;eachnewunitisconcreteddirectlyagainsttheprecedingoneandafterithashardenedtheresultantstructureismovedforwardbythelengthofoneunit(fig.1).Thisprinciplehasalreadybeenusedformanyyearsintheconstructionof

3、steelbridges.Thisishardlysurprising,inviewoftheequalstrengthofsteelintensionandcompressionsince,providedthedesignissuitable,thealternatingstresseswhichoccurwhenthebridgeisslidforwardscanbeacceptedwithoutdifficulty.Thisisnotsowithconcrete,whichcanwithstandonlysmalltensilestresseswithout

4、damage.Specialmeasuresarethereforenecessarytoenableconcretebridgestobeslidforwardbysteps;theskilfuluseofprestressingisthemostimportantofthesemeasures.Theincrementallaunchingmethodasappliedtodayforprestressedconcretebridgeswasfirstusedin1965attheInnBridgeKufstein,Austria.AftertheSecondW

5、orldWar,bridgesweredesignedontheprincipleoftheminimumconsumptionofmaterials.Lateron,thelaborcomponentoftheconstructioncostsbecameincreasinglylarge,asaconsequenceofthe52complicationofformworkandfalsework,sothatconstructionmethodswhichwerelesslabor-intensivecametothefore,inwhichacertaine

6、xcessconsumptionofmaterialswasmorethancompensatedbysavingsinthelaborcosts.Theseconditionsareespeciallypredominantintheincrementallaunchingmethod.Thedevelopmentofteflonandrelatedproductswhichenableslidingofunitstobecarriedoutwithalowcoefficientoffrictionfinallyprovidedtheconditionsinwhi

7、chthemethodcouldbeusedwithsuccess.Theincrementallaunchingmethodisgenerallyeconomicalforbridgesofspansof30to60mandalreadyforquitesmallprojectsoflengthsexceedingabout150m.Bytheendof1976about80bridges,havingatotalareaofabout300,000m2(equivalenttoatotalof25kmofbridgesof12mwidth)hadbeenco