Analysis Of Prestress Distribution Of Long-span PC Continuous Rigid Frame Bridge

Prestressed technology had been used in concrete at the nineteenth century,it means the prestressed concrete technology(PC Technology)having sprouted.With the technology developing,people tried to use it in bridge which formed the initial prestressed concrete bridge.By 1930 s,70% of the world’s bridges had used PC technology.Along with the extensive application of the PC technology in bridge engineering,a series of diseases such as concrete deterioration,prestressed reinforcement defection,midspan deflection and so on had begun to appear,especially on large-span PC continuous rigid frame bridge.At present,the main methods to deal with these diseases are external reinforcement,reducing load,replacement of beam body,and so on.It have failed to start from the distribution of the prestress along the path which determining the force condition of the bridge,and to prevent it fundamentally.In this paper,the finite element analysis about distribution of the prestress of prestressed reinforcement and box girder structure has been carried out focusing on the analysis of long-span PC continuous rigid frame bridge which is influenced strongly by distribution of the prestress and its prestressed reinforcement.In the first,the main works incloudes making the definition of the distribution of the prestress and its analysis.Showing that analysis can be divided into two stages including different research object beteen prestressed reinforcement and box girder.Pointing out that the prestress loss and the poor distribution along the path of the prestressed reinforcement are the main reasons for the long-span PC continuous rigid frame bridge’s problems such as the midspan deflection,the girder crack and so on.Summarizing that the methods of quality controling and evaluation for the prestress system which are adopted at present.Pointing out that there are qualitative requirements causing some problems such as quality difference.On the foundation of existing data which were collected,and summarizing current existing theory and method of the distribution of prestress along the path,and assureing the contrast basis and reference for analysis is Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts.Then,in order to analyse the prestress on prestressed reinforcement,established,analysed and compaered 5 kinds of models that are "box girder entity unit-prestressed reinforcement entity unit(full contact)","box girder entity unit-prestressed reinforcement entity unit(real area form)","box girder entity unit-prestressed reinforcement plate unit","box girder entity unit-prestressed reinforcement beam unit" and "box girder plate unit-prestressed reinforcement plate unit" basing on the finite element contacting analysis software Midas/NFX.Selecting "box girder plate unit-prestressed reinforcement plate unit" model as the best model for analying of prestress on prestressed reinforcement and optimizated it.Subsequently,in the the first stage of distribution analysis,choosing the prestressed reinforcement in long-span PC continuous rigid frame bridge as research object and using " box girder plate unit-prestressed reinforcement plate unit" model as calculate model type to calculate process in the case there prestressed reinforcement shape and materials,tension control force,friction coefficient is changing,for realizing calculation of prestress loss and distribution on prestressed reinforcement.And showing the analysis results on specification modification and parameter modification.Putting forward that the "peak clipping effect" existing in practical engineering which causing the calculated value of the process retraction loss is not suitable for actual situation.Finally,in the the second stage of distribution analysis,putting forward the elastic connection method for simulating contacting situation between prestressed reinforcement and hole at long-span PC continuous rigid frame bridge in tensioning period.Calculating and fitting empirical formula which showing relationship among normal stiffness coefficient of elastic connection and friction,unit size,friction coefficient between prestressed reinforcement and hole,curvature radius of prestressed reinforcement and bending angle of prestressed reinforcement.Taking Chongqing Gaojia Huayuan Jialing River Compound Bridge as engineering examples.Using the equivalent load method Which is used to simulate prestressing effect(beam element model)and elastic connection method(distribution analysis model)to calculat and analysis the situation of changing of elevation and stress after tension of prestressed reinforcement on four sections per piers at river side and shore side.Then,contrasting the calculation results with the measured data.Proving it is feasible that using the elastic connection method to simulate the friction between prestressed reinforcement and hole of box girder and calculate prestressed effect of structure.