Study On Shinkage And Creep Of Concrete Filled Steel Tube

With the use of concrete filled steel tube in high-rise buildings and long-span bridges, long-term deflection and internal force redistribution and other issues caused by shrinkage and creep of concrete have become increasingly prominent. It will affect the long-term behavior of concrete filled steel tubular structure. Thus, shrinkage and creep of concrete filled steel tube can not be ignored in the engineering design.For CFST(Concrete Filled Steel Tubular), the shrinkage of core concrete is far less than creep, because the core concrete of CFST has no contact with the outside. The interaction of core concrete and steel tube is very complex. Core concrete is in three-dimensional stress state, so redistribution caused by core concrete creep is more complex than ordinary concrete. Thus, creep study of CFST is necessary.In the thesis, based on the field experiment on Beipanjiang bridge model, contrast test for plain concrete and CFST was conducted to explore the creep and shrinkage law of CFST.Meanwhile, the field experiment data of plain concrete was fitted.Because of the complex interactions of core concrete and steel tube, one direct calculation method and two finite element calculation methods are proposed to obtain creep of concrete filled steel tube.(1) Based on deformation compatibility conditions of core concrete and steel tube and ignoring the impact of concrete loading age, the relationship between creep deformation of concrete filled steel tube and time was derived with the age adjusted effective modulus method.(2) Considering the impact of concrete loading age, the finite element software ANSYS was used to calculate last time creep strain by dividing the time into a series of period and superimposing product of creep coefficient and the strain component of respective.(3) Stress-strain relationship at any time point is derived with the age adjusted effective modulus method. Then creep deformation was made into elastic deformation to calculate creep deformation at any time point.The finite element solution of concrete filled steel tube creep can be achieved by secondary development of ANSYS using parametric design language(APDL). Meanwhile, the effects of steel ratio on creep was also studied. Finally, MIDAS CIVIL was used to establish full bridge finite element model to do simulation analysis of the construction phase.