Research On The Prestressed Concrete Continous Girder Bridges With Very Long Prestressing Strands

Due to the characteristics of prestressed concrete continuous girder bridge and the improvement of modernization construction,prestressed concrete continuous girder bridge is the first design choice when the span of the bridge is in the range of 400 meters. Excessive loss of prestress can cause midspan downwarping and crevice in bridge structure during the prestressed concrete continuous girder bridge is working.Loss of prestress decide the crack resistance and deflection directly. According to overlong prestressed reinforcement in prestressed concrete continuous girder bridge,its prestress is affected by many factors and result in its loss of prestress larger than short prestressed reinforcement. So,it is necessary to study the loss of prestress for prestressed concrete continuous girder bridge with overlong prestressed reinforcement. Based on the analysis and conclusion of the development and research status of prestressed concrete continuous girder bridge at home and abroad,three-span prestressed concrete continuous girder bridge in Changzhou is the object of study.This article is researching for loss of prestress about the prestressed concrete continuous girder bridge. This article mainly has the following several aspects of research:First of al,using the finite element software cal ed Midas/Civil built the real bridge modal. Through changing the size of the discount of loss of prestress in different positions, the article researchs the influence of the the span centre deflection.According to the calculation result, the different discount of loss of prestress in different positions has the huge influence of span centre deflection. The influence order from strong to weak is the roof prestressed reinforcement,the web prestressed reinforcement,the baseplate prestressed reinforcement.Different prestressed stretching will produce the Crankle coupling effect. To ensure that the bridge structure deflection change and stress increment are relatively flat,I compare and analyze the different prestressed tensioning sequence. Through calculation and analysis, the best of prestressed steel beam tensioning sequence is the web prestressed reinforcement,the baseplate prestressed reinforcement,the roof prestressed reinforcement.By changing the pipe friction parameter of prestressed reinforcement in the finite element model,I research and analyse the influence rule about pipe friction parameter to the deflection and stress in the whole bridge. Through calculation and analysis,the pipe friction parameter has a big impact on the deflection and stress and a small impact on the deflection and stress in the whole bridge.The size of the μ has a biger impact on the deflection and stress in the whole bridge than the size of the k.The pipe friction loss is an important part of the loss of prestress about prestressed concrete continuous girder bridge. The test result of Pipe friction parameter is useful for realizing the loss of prestress in the actual construction process. It provides the basis for construction control.According to the test result,the measured values of μ and k is 0.42 and 0.006. It is biger than specification values. The test result shows that the actual loss of prestress is too large.In the end,The current specification has on definite provision of the initial tension stress and hold time about super-long prestressed steel beam. Through field test to determine the initial tension stress and the hold time of super-long prestressed steel beam,it can Provide guidance to the actual prestressed tensioning construction. The experimental results showed that the initial tension stress should be set to thirty percent of tension control stress and the hold time should be set to at least 8min.The research shows that the study about loss of prestress of the prestressed reinforcement can provide the basis and the reference about the same type bridge design and construction of prestressed. Field test of super-long prestressed steel beam is very necessary. It can has a very good guidance for the prestressed tensioning construction.