| Concrete filled steel tube(CFST)structure has high bearing capacity,good ductility and superior seismic performance,therefore,CFST column frame system is often used in high-rise steel structure residential system.In CFST residences,the width of the wall is usually 150～200mm,and the width of the steel tube is usually 300 mm,it is easy to cause the problem of exposed columns in the residence.The short side dimension of the cross section of the CFNST column is smaller.The short side of the cross section of the CFNST column is small,which can be perfectly hidden in the building wall to meet the needs of building layout.Based on the research of CFST column,the compressive performance of CFST column is studied,and an improved CFST columnH-beam joint is designed to study the seismic performance of the joint.The main research contents of the paper are as follows:(1)The compressive properties of CFNST columns with dimensions of195×75×600mm are studied.The typical failure modes of axial compression specimens and eccentric compression specimens are clarified,the effect of eccentricity on the bearing capacity and ductility of CFST columns is studied,the variation law of longitudinal strain and transverse strain of the steel tube during the loading process is analyzed,and verifies the plane section assumption of the eccentric compression specimen.(2)The finite element analysis of the compressive performance of the CFNST column is carried out.Through finite element analysis,the difference between the CFNST column and the concrete restraint effect inside the square concrete filled steel tube column is compared,the influence law of section height-width ratio,section size,steel tube thickness and slenderness ratio on the axial compression of flat steel tube concrete columns is clarified,the difference of the internal concrete stress distribution of the axial compression specimen under different height-width ratios is analyzed,the influence law of the eccentricity,section size,steel tube thickness and slenderness ratio of the specimen on the eccentricity performance of the CFNST column is obtained.(3)The axial and eccentric bearing capacities of CFNST columns in the finite element parametric analysis are calculated using different codes,and the bearing capacities calculated by the codes and those calculated by finite element are compared and discussed,and the results show that JGJ138 is the most accurate in predicting the axial compressive bearing capacity of the specimen,and the EC4 specification can more accurately predict the eccentric bearing capacity of the specimen.(4)Two improved CFNST column-H-beam joints are tested and studied,and two failure modes of the joints are expounded,the skeleton curve,ductility,energy dissipation capacity and stiffness degradation of the joints are obtained by adding the hysteresis curves of the nodes to obtain the seismic performance indexes of the nodes,and the strain laws of the columns and beams of the nodes are explained.The results show that the nodes have good ductility and energy dissipation capacity.(5)The parametric analysis of the joint is carried out,and the influence of the parameters such as the thickness of the local thickening area,the height of the local thickening area,and the axial compression ratio on the seismic performance of the joint is studied,the results show that the thickness of the local thickening area of the column wall should not be less than 16 mm,and the height of the local thickening area should be at least 150 mm beyond the upper and lower flanges of the steel beam.When the thickness of the local thickening area is 16～20mm,the seismic performance of the joint is not affected by the axial compression ratio.(6)According to the relevant specifications,the design and calculation method of the core area of the joint is proposed,and one of the test nodes is selected to use the design method for verification. |
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