Study On The Axial Compressive Mechanical Properties Of T-shaped CFST Columns With Inner Steel

Steel and concrete composite structure can make up for the defects of the two materials,therefore it is widely used in the field of civil engineering.Compared with the traditional square and rectangular cross-section columns,the special-shaped cross-section columns represented by T-shaped,L-shaped and cross-shaped columns are widely favored by people because they can effectively avoid the convex edge problem of columns in high-rise building structures,improve the use area of rooms and improve the layout of rooms.At present,the special-shaped section columns mainly include reinforced concrete special-shaped section columns,steel tube concrete special-shaped section columns and steel reinforced concrete special-shaped section columns.On the basis of summarizing the advantages and disadvantages of the above special-shaped columns,this paper proposes a new special-shaped cross-section column,namely T-shaped CFST columns with inner steel.Through experimental research,theoretical analysis and numerical simulation,the mechanical properties and working mechanism of this special-shaped column under axial compression were analyzed in depth,which provided a basis for studying its mechanical properties under eccentric compression and bending.To study the axial compression performance of special-shaped CFST stub columns with inner steel,nine T-shaped CFST stub columns with inner T-shaped steel and three T-shaped CFST stub columns without inner T-shaped steel were tested under axial compression.The failure modes of the specimens were investigated.Besides,the changes of Load-strain（N-?）curves of tube steel,N-εcurves of reinforcing steel,Load-average longitudinal strain curves were analyzed.Moreover,the effects of parameters such as steel content rate,steel tube confinement index and built-in steel ratio on the bearing capacity of the specimens were also discussed.The results show that the failure mode of all specimens under axial compression is local buckling failure.While keeping other factors constant,the ultimate bearing capacity of the specimens with 4mm,6mm and 8mm steel increases by 42.9%,56.5%and 67.2%respectively.When the thickness of steel tube increases from 3mm to 4mm and 5mm,the ultimate bearing capacity of the specimen increases by 5.4%and 11.1%respectively.However,with the increasing thickness of steel and steel tube,the enhancement ability of the ultimate bearing capacity of the specimen is gradually weakened.In order to further study the mechanical properties of T-shaped CFST stub columns with inner T-shaped steel under axial compression,on the basis of experimental research,the finite element software ABAQUS was used to establish the corresponding model for comparative analysis.The effects of steel tube yield strength,steel yield strength and concrete strength on the ultimate bearing capacity of T-shaped steel reinforced concrete filled steel tubular stub columns were studied.The results show that the finite element simulation results are basically consistent with the failure mode obtained by the test,and the bearing capacity of the specimen is also consistent with the corresponding curve of the steel tube.The increase of yield strength of steel tube,yield strength of steel and concrete strength can improve the ultimate bearing capacity of the specimen,and the yield strength of steel tube has a great influence.In order to further study the working mechanism of T-shaped CFST stub columns with inner T-shaped steel,the working mechanism of the component was analyzed in detail on the basis of experimental research and finite element analysis.Through the results of finite element simulation,the failure mode,core concrete stress field,steel tube stress field,steel stress field and contact stress of typical specimens were analyzed and studied.The results show that the configuration of steel can enhance the deformation capacity of the specimen;the stress at the corner of the three limbs of the core concrete is large,and the stress at the corner and the middle area of the long straight edge is small.The stress in the corner and middle area of the steel pipe is large,and the stress at both ends is small.The stress in the middle of the steel is large,and the stress at both ends is small;the normal contact stress between the steel tube and the concrete is larger in the positive angle of the steel tube and the near part of the steel tube,and the middle area of the long straight edge and the negative angle of the steel tube are smaller.Based on experimental research and parameter analysis,referring to the calculation formulas at home and abroad,after comparative analysis,according to the calculation formula of axial compression ultimate bearing capacity of steel reinforced concrete filled steel tube short column,the equivalent constraint coefficientξ_eq is used to consider the constraint of steel tube on core concrete,and the calculation formula of ultimate bearing capacity of T-shaped CFST stub columns with inner T-shaped steel is proposed.The calculation results are in good agreement with the experimental results and finite element results.