Research On Incremental Launching Technology For The Girder Of Long Span Deck Steel Truss Arch Bridge

Incremental launching is an important methodology for bridge construction which can date back to 1959.Incremental launching can go with light and simple construction equipments,it has nearly no impact on traffic,it provides good environment for workers.Moreover,incremental launching is easy for construction management.It is very suitable to use incremental launching in rivers,in the deep valley and cross-line projects,more than one thousand bridges have been built at home and abroad with this method.However,during incremental launching process,the boundaries of the steel box girder are constantly changing,each of the cross section must undergo alternating changes of positive and negative bending moments,which makes the stress of the girder become complicated.For the girders of long span deck steel-trussed arch bridges,comparison of construction technology,optimization of design parameters of steel nose,linear shape of girders during launching,and impact of incremental launching on the stability of arch columns have yet to be further studied.Through consulting a lot of references,this paper traced the origin of the incremental launching methodology and summarized its development overview,classification method,temporary facilities,and technical limitations.Taking the nujiang Bridge of Darui Railway as the engineering background,the model was innovatively constructed by the grid method to more accurately simulate the counterforce and deformation and simplify the calculation.The influences of three parameters,including the length,unit weight,and stiffness of the steel nose on the performance of the beam were analyzed by analytical methods.The rationality of parameter selection was verified by the finite element calculation results.The Incremental launching process of the whole girder was divided into 79 stages for simulation analysis,the maximum stress and deflection of each cross section of the main girder during the incremental launching process and the maximum supporting force of the columns on each arch were traced.The elastic buckling analysis of the bridge was performed on the maximum supporting force conditions of the column and the results showed that the stability of the bridge during the incremental launching process meets the requirements.The local analysis of the steel box girder under the maximum supporting force conditions was performed to obtain the stress distribution of each plate of the steel box girder,and the safety of the beam during the launching process was evaluated and suggestions for improvement were proposed.