Analysis Of Creep And Shrinkage Effects For Super Long-Span Concrete Arch Bridge With Cfst Stiffened Skeleton

Super long-span concrete arch bridge with concrete-filled steel tube stiffened skeleton is an important development for modern arch technology. Due to its excellent mechanical properties, concrete-filled steel tube has been demonstrated to be one of the major schemes for stiffened skeleton. Enveloping concrete around stiffened skeleton may result in significant difference between ages of concrete at different part of the same section. Meanwhile, since the filled-in concrete is sealed by tube which makes moisture migration hardly occur, the shrinkage and creep of filled-in concrete may obviously differ from those of enveloping concrete. Those remarkable features cause complicated long-term time-variant effects. However, analysis of creep and shrinkage effects of super long-span concrete arch bridge with concrete-filled steel tube skeleton is far from perfect.Based on the Beipanjiang super long-span railway concrete arch bridge under construction, the effects of shrinkage and creep on concrete arch bridge with concrete-filled steel tube stiffened skeleton are investigated by a finite element software based on the theory of degenerated beam element. The long-term deflection and stress redistribution are studied. The main work is as follows:1. The theory of shrinkage and creep analysis based on degenerated beam element is adopted to analyze the effects of shrinkage and creep of Beipanjiang super long-span concrete arch bridge with concrete-filled steel tube skeleton. The age differences of the various stages and the various parts of the same section of concrete are considered with this method.2. Research development on concrete shrinkage and creep home and aboard is collected. The mechanism of concrete shrinkage and creep is studied. The basic concepts, the creep coefficient and the shrinkage strain in shrinkage and creep prediction model is introduced. Considerations, scope, and reliability on the prediction model is also compared.3. The long-term deflection and stress redistribution are studied with CEB-FIP78model, the CEB-FIP90model and GL2000model, and the influences of various models about shrinkage and creep, reinforcement, concrete loading age, tube cross-section dimensions on computational results are also discussed. It is shown from the numerical results that bridge deformation after completion is far greater than the upper limit of adjustment of common ballastless track fastener (20mm). Thus, bearing with large vertical adjustable range is expected. Attention should be paid on the yield risk of some parts of the steel tube and the high stress of filled-in concrete. In order to effectively decrease the long-term deformation and reduce the stress of the steel and concrete, the diameter of steel tube is suggested to be increased in the following similar engineering practice.