Key Construction Technique For Closure Launching Of The Continuous Rigid Frame Bridge Considering Large-deviation And Large-tonnage

Continuous rigid frame bridge is one of the most widely used bridge types in China because of its strong spanning capacity,smooth driving and convenient construction.Closure jacking is one of the key construction links of continuous rigid frame bridge,and its construction quality will directly affect the later operation safety and stress distribution of the bridge.In view of the continuous rigid frame bridge,a large number of scholars and engineers have carried out in-depth and systematic research on the calculation of jacking force,loading mode and construction technology,and achieved fruitful results.But for the railway continuous rigid frame bridge,due to different design standards,the rigidity of the pier is often greater than that of the highway pier,and the required jacking force will exceed 3500 k N.Large tonnage jacking will cause large deformation of the cantilever beam at both ends of the closure section,and may cause local cracking of the concrete box girder.In view of this problem,this paper puts forward four point synchronous jacking construction technology of closure,and takes a super continuous rigid frame bridge in Northwest China as the engineering background,calculates the jacking force required for closure of the bridge,analyzes the influence law of jacking force on the deformation and stress of box girder in different stages.In addition,through numerical simulation,the paper studies the local stress and deformation rule of the box girder section under the traditional two-point jacking and the proposed four point jacking,and analyzes the influence of the location,height and loading mode of the steel base plate on the local stress of the box girder,so as to provide technical reference for similar railway bridge closure jacking construction.The main research contents and conclusions are as follows:(1)In view of the complicated calculation method and the complicated coupling of the influencing factors of the jacking force,a simplified calculation method of the jacking force is proposed.Considering the effects of temperature,concrete shrinkage and creep,construction defects on the jacking force,based on the principle of deformation equivalence,the fitting formula of the jacking force of the bridge closure is given,which simplifies the calculation of the jacking force.Taking a super large continuous rigid frame bridge of Northwest Railway as the research object,the displacement of pier top under the action of temperature,concrete shrinkage and creep,and construction defects is analyzed by establishing a finite element model,and it is concluded that the required thrust of closure top is 5000 k N,and the maximum deflection of box girder at both ends of closure is 211.7m。(2)In order to solve the problem that the traditional two-point jacking construction is difficult to achieve large tonnage jacking closure,a new construction technology of jacking closure based on four-point loading is proposed.A special jack loading device for four point jacking is designed,and the problem of Jack deviation caused by large deformation of box girder at both ends of the closure jacking is overcome by setting the hinge structure measures;Finite element analysis is used to check the local bearing capacity of the box girder under the action of four jacking points,and the influence of jacking on the local stress of the box girder is reduced by optimizing the height of the base plate,the position of the base plate and applying the unbalanced jacking force.The results show that the maximum tensile stress of the box girder concrete is 1.48 mpa,which meets the requirements of the code.When the deviation between the height of the base plate and the top thrust of the four points is 5%,the local stress of the box girder is obviously improved.(3)In view of the new construction technology of four point push closure,the finite element simulation method is used to analyze the influence law of push closure on the stress and deformation of the whole bridge in different stages such as completion and operation of the bridge for 10 years,and to compare it with the actual deformation data in the process of jacking and completion of the bridge,so as to verify that the construction technology of push closure based on four point loading can resist the shrinkage of temperature and concrete in engineering application The negative moment caused by the loss of prestress and strain can obviously improve the overall mechanical performance of the bridge and extend the service life.