Research On The Axial Compression Performance Of T-shaped Thin Walled Concrete-filled Steel Tubular Stub Columns With Bar Stiffeners Under Constant High Temperature

T-shaped thin walled concrete-filled steel tubular column with bar stiffeners is a new type of thin walled composite structure,which was formed on the basis of ordinary T-shaped CFST columns,welding bar stiffeners in steel tube,and further reduce the thickness of steel plates.This novel structure is easy to meet the requirement of architectural plane.It can improve the mechanical properties of ordinary T-shaped CFST columns and then reduce the construction cost,which has the advantages both of the special-shaped reinforced concrete columns and the CFST columns.At room temperature,bar stiffeners can delay the local buckling due to the decrease of the steel tube's thickness,significantly reduce the consumption of steel plates,its mechanical properties can also meet the requirements of the building structure.Under fire exposure,with the increase of temperature the loss of the material's mechanical properties were more serious,the lateral outward deformation of core concrete and the steel plates are both constrained by setting reinforcement ribs,and thus improved the mechanical properties of the whole structure.For the building structure,which can not only reduce the loss of the bearing capacity of the column under fire,prevent the occurrence of collapse,but also provide more choices for the subsequent structure's repairment and reinforcement.In this paper,the experimental study and finite element analyses on the axial compression of the T-shaped thin walled concrete-filled steel tubular stub column with bar stiffeners are carried out,and the main contents as follows:(1)Six T-shaped thin walled concrete-filled steel tubular stub columns with bar stiffeners and two without were tested under constant high temperature,the axial load-displacement relationship curves,failure modes and the core concrete's failure characteristics were recorded and discussed.The results show that the lateral outward deformation of steel plates was constrained and the steel plates' s confinement effects on core concrete were enhanced by setting reinforcement ribs,therefore,improved the axial compressive performance of the specimens.With the increase of temperature,the load-displacement curves tend to be flat,the ultimate bearing capacity decreased obviously,and the displacement of the ultimate bearing capacity increased significantly.(2)A finite element(FE)model was developed with the program ABAQUS,featuring heat transfer analysis and axial stress analysis,the reliability of the FE model was validated by the good agreement between the theoretical results and theexperimental data,and than analyse the mechanism of the specimens.The results show that the vertical stress distribution of the core concrete in the section of the temperature contrast columns is that the corner region is maximum,the middle area of concrete second,and the angle area lowest.For the bar stiffeners contrast columns,the stress distribution is usually uniform because of the restraint of bar stiffeners.(3)Based on the finite element model,the influence of main parameters,such as test temperature,bar stiffeners vertical spacing,the thickness and the yeild strength of steel plates,the strength of core concrete,on the axial compressive performance of the specimens were discussed.Based on the results of parametric analyses,simplified formulas were proposed for predicting the evaluating indicators of T-shaped thin walled concrete-filled steel tubular stub columns under constant high temperature,which may be a reference for this kind of column used in practical engineering.