Effects Of Creep On Bonding Property Of Concrete Filled Steel Tube Members

Popularly applied in engineering, Concrete Filled Steel Tube(CFST) structure features bonding property which exists between steel tube and core concrete. This property not only makes the load to be delivered between steel tube and concrete, but also allows the two materials to cooperate and work together. However, the bonding property of encased structure is more complex in actual engineering.Realizing the significance of the research on bonding property of CFST, this paper mainly focuses on effects of creep on the adhesiveness of CFST axially compressed members and on the cross-section stiffness of eccentrically compressed CFST after debonded. The following is the main contents presented in this paper:(1)On the basis of plane strain theory of concrete and creep theory of CFST, this paper develops a computational model for both interface radial stress and shear stress between steel tube and concrete considering creep of CFST axial compression members. Then, the author used the model to several examples and the results show that the interface stress is mainly by shear stress under axial compression and creep may reduce the radial adhesiveness of CFST axial compression members, but is useful to improve its shear adhesiveness. the radial and shear adhesiveness of CFST decrease as steel ratio increases, in that case the author consider to increase the bonding property of CFST by reduce the steel ratio so as to improve the condition of component coordination; The radial stress increment may exceed the component adhesive strength with creep, causing the member section debonding.(2)This paper builds a computational model for section debonding height when CFST is under compressed eccentrical loads. That is, this model is designed to calculate the cross-section debonding height in the situations of different loads and eccentricity ratio considering creep. The results show that the compressed area of CFST eccentrically compressed members would partial debond; that the cross-section debonding height decreases during the creep, which explain effcets of creep on the bonding property of CFST eccentrically compressed members is favorable; that the cross-section debonding height increases basically as loads and eccentricity ratio increase.(3)This paper comes up with a computational model for steel tube’s non-uniformly distributed strain coefficient of CFST eccentrically compressed members after debonded. Based on the model and theory of material mechanics, the author suggests a new computational model for cross-section stiffness in consideration of non-uniformly distributed strain coefficient of steel tube. Finally, it comes to the conclusion that the cross-section section stiffness can be enhanced as the CFST eccentrically compressed members debonds.