Deflection Analysis And Secondary Tension Settings Research For The Wide Span PC Continuous Right-frame Bridge

With the development of the transportation, China’s large spanprestressed concrete continuous rigid frame bridge are widely used inbridge construction because of its features. But the midspan deflectionproblem has become an urgent difficult problem. In the past engineeringcalculation, usually by camber preset, external prestressing beam method toprevent excessive midspan deflection, which can not effectively reduce thedeflection, but also increase second investment cost of theproject.Therefore, research on this issue is imminent, in order to providethe reference for the designment.This paper firstly summarizes the research on creep of concrete theoryand calculation method, and elaborated the theoretical analysis andcalculation steps for creep calculation in Midas program. Secondly,combined with engineering practice, takes Yuanshui bridge, Furong Bridge,Jinsha River bridge, Huangshi Yangtze River Bridge and Humen AuxiliaryNavigation bridge as the background, using the finite element softwaremidas/civil to model analysis, conducts the research to the pre-stressedfriction loss, given the design reference to the propose to amplify the valueof the friction coefficient of prestressed reinforcement and wall pipespecification and the influence coefficient on friction of pipes per meterlocal deviation, recommend coefficient k is0.003~0.004/m, coefficient u is0.3~0.35are appropriate. At the same time, the prestress loss caused byexcessive midspan deflection were analyzed, and compared with themeasured deflection monitoring data, and conclude that the midspandeflection of7years after the finished bridge is consistent with the modelof prestress losses of30%.Finally, in order to improve the main girder midspan deflection, wepropose that give the bridge2nd time tension, that means to reserve ofprestress duct in bridge design, and give the bridge2nd time tension at thecertain number of years of the bridge when the midspan deflection is large,make the bridge mid-span deflection recovers to the original design level.According to the five bridges in actual model to analyze prestressed2ndtime tension setting mode, we should be in the distance across the4~6 cantilever segment tensioning plate later beam, tension control in30%afterthe tension is scheduled for completion after two or three years, ensuringthe maximum pressure structure of floor stress meet the relevant standard,give the bridge2nd time tension according to normal processrequirements. In accordance with the above measures, the2nd time tensionwill effectively improve the long-span bridge midspan deflection problem.