To study the bond mechanism of steel tube and concrete interface

referring to the method of setting geometric defects in steel structure design code

low-order buckling modes were used to characterize the overall geometric defects and high-order buckling modes were used to characterize local geometric defects. The contact element was set with 100 layers of contact pairs

and the interface bond-slip behavior was defined by the Coulomb friction and sliding criterion. ANSYS restart analysis function was adopted to realize the gradual loss of chemical bonding force

and the finite element model of concrete filled steel tube with geometric defects was established. Simulation results show that the low-and high-order buckling modes of steel tubes were suitable for simulating the overall and local geometric defects of steel tubes

and the superimposed defect size could simulate the geometric defects of ±0.5%D (Dis the outer diameter of the steel tube). The finite element model (FEM) could monitor each load step

describe the time-varying state during the push-out process more accurately

and reproduce the process of the gradual peeling of the steel-concrete bond interface from both ends to the middle of the specimens. The overall geometric defects of the steel tubes corresponding to the two types of bond-slip curves included a downward trend curve after the formation of the inflection point

which corresponds to the low-order buckling mode of the linear meridian

and a slow rise curve after the formation of the inflection point

which corresponds to the low-order buckling mode of the curved meridian. The local geometric defects of steel tubes could be summarized as periodic wave crest-like defects. The empirical relationship between the number of local geometric defect crests and the diameter-thickness ratio of steel tube

bond length

as well as concrete strength was proposed.