Post-fire Behaviors Of T-shaped Stiffened CFST Stub Columns Under Axial Compression

T-shaped stiffened CFST columns are based on ordinary T-shaped CFST columns,adding stiffening steel to delay the local buckling of the steel tube,and improve the interaction effect between the steel tube and the concrete to achieve the purpose of improving the mechanical properties of the component.Owing to its unique cross-section,this type of component avoids the problem of the exposed column in the building structure and greatly reduces the construction cost.It is suitable for the frame structure of high-rise and super high-rise buildings.In recent years,domestic scholars have carried out a lot of research on the mechanical properties of the members at room temperature,and have recognized the failure modes and bearing factors of T-shaped stiffened CFST columns subjected to concentric and eccentric compressive loads.Based on the previous research results,this paper,considering the possible exposure modes of T-shaped stiffened CFST stub columns in actual engineering,conducts experimental research and finite element analysis on the axial compression behavior of the components after fire.The main work and results of this paper are listed as follows:?1?The axial compression performance test of eight T-shaped stiffened CFST stub columns was carried out,and the test variables included:exposure mode,heating time and the presence or absence of stiffening bars.The test results show that for uniform fire conditions,the residual bearing capacity and axial stiffness of T-shaped stiffened CFST stub columns decrease with the increase of heating time,and the ductility increases with the increase of heating time.For non-uniform fire conditions,the T-shaped stiffened CFST stub columns after fire have the possibility of increasing the residual bearing capacity and the axial stiffness with a short heating time,and the ductility decreases slightly.For non-stiffened specimens after fire,the residual bearing capacity and axial stiffness are close to the stiffening specimens,but their ductility is weak.?2?The ABAQUS finite element software was used to establish the T-shaped stiffened CFST stub columns model after fire,and the calculated value was compared with the experimental value to verify the accuracy and reliability of the model.Through the model,the force analysis mechanism of the specimen is deeply analyzed.The load partitions of concrete and steel tube,the interaction between concrete and steel tube,and the longitudinal stress distribution of concrete during axial compression are explored.?3?The ABAQUS finite element software was used to further study the effects of material strength,steel tube thickness,longitudinal spacing of stiffened steel bars,section parameters and heating time on the residual bearing capacity of T-shaped stiffened CFST stub columns subjected to different exposure modes.The results show that the residual bearing capacity of T-shaped stiffened CFST stub columns with different exposure modes has a similar influence law,that is,the residual bearing capacity is significantly decreased with the increase of heating time and flange width ratio?a₁/b₁?,and increased with the increase of the material strength,the thickness of the steel tube,and the section perimeter.?4?Based on the calculation formula of ultimate bearing capacity of T-shaped stiffened CFST stub column at normal temperature,the equivalent strength of concrete and steel tube after fire is considered,and the calculation formula for the residual bearing capacity of T-shaped stiffened CFST stub columns after uniform fire and non-uniform fire is established.