Research On The Influencing Factors And Corresponding Solutions In The Widening And Connecting Of Multi-span Prestressed Concrete Continuous Box Girder Bridges

In dealing with the problem of the widening and connecting of prestressed concretecontinuous box-girder bridges, there are many choices, the optimal solution of which is theone-time rigid connection through the flanges between newly-built and existing bridges.However, this method has the greatest impact on the main girders and flanges of thenewly-built and existing bridges.Based on the real bridge widening project and focusing onthe mechanical problems of the widening and rigid connecting of multi-span prestressedconcrete continuous box-girder bridges, this thesis discusses these questions.1. After reviewing the application and history of the widening and connectingconformation of bridges, this thesis summarizes the research on the mechanical behavior ofconnected bridges systematically.2. This thesis introduces several basic analysis theories associated with the widdeningand connecting of bridge structures, including shear flexible lattice beam theory, solid finiteelement theory of prestressed concrete structures and basic theory of concrete creep, for thestructural analysis below.3. Based on8×30m finite element models of the prestressed concrete continuousbox-girder bridge, this thesis analyzes the mechanical behavior of the whole structure and thepartial structure in the cases of the newly-built and existing bridges are connected anddisconnected. It turned out that:①the dead load and the vehicle load have the greatestimpact on the mechanical behavior of the whole structure with the newly-built and existingbridges being rigidly connected, while the effect of differential foundation settlement betweennewly-built and existing bridges and the effect of temperature impact relatively little under thesame condition.The mechanical behavior of the whole structure does not control the design.②the concrete shrinkage and creep, differential foundation settlement between newly-builtand existing bridges and temperature gradient have the greatest impact on the mechanicalbehavior of the local structure; the connecting flange can easily crack, however, incomparison with which, the vehicle load effect impacts relatively little.4. Based on the analysis, this thesis proposes several solutions which are verified byFEM to improve mechanical behavior through Concrete shrinkage and creep, vehicle load anddifferential foundation settlement between newly-built and existing bridges.Main results:①measures such as application of high performance concrete materials, delaying the splicing time of newly-built and existing bridges and optimizing the construction technology of thepost-pouring band of the splicing flange can reduce adverse impact on bridge structures, dueto the effect of concrete shrinkage and creep.②meanwhile, a series of measures such asreducing pile foundation settlement after construction and so on can be used to reduce oreliminate adverse impact on connecting structures caused by the effect of differentialfoundation settlement between newly-built and existing bridges.③Regularity of theinfluence on the mechanical behavior of the local structure is inconsistent or opposite, due tothe relative vertical bending stiffness of newly-built and existing bridges and the stiffness ofconnecting flanges under the effect of the vehicle load and differential foundation settlement,therefore, the value of which should be considered carefully.These conclusions can provide some guidance and help for the issues of bridge wideningof similar structure.