Study On Mechanical Properties Of Concrete Filled Steel Tubular Columns Under Axial Compression

Under the premise of ensuring structural safety,people are paying more and more attention to the aesthetics,economy and functionality of the building.In order to meet the complex function of buildings and the individualized aesthetic needs,more and more buildings will inevitably be applied to special-shaped concrete-filled steel tubular members.At present,research at home and abroad mainly focuses on the axial and eccentric compressive strength of circular and rectangular concrete filled steel tubular columns,but the research on the mechanical properties of special-shaped columns is still rare.Therefore,it is necessary to study the mechanical properties of special-shaped concrete filled steel tubular columns.Therefore,this paper taked L-shaped columns as the research objects.According to the existing test results and the fiber element model program,the mechanical properties of the concrete filled L-shaped steel tubular members were studied.The main research contents are as follows:(1)Based on the research background of concrete filled steel tubular composite structures,the present situations of mechanical properties of concrete filled steel tubular columns were studied(Chapter 1).The research status of concrete filled steel tubular(CFST)with common section was analyzed,and the research status of axial and eccentric compression performance of special-shaped CFST columns was summarized.The existing problems of L-shaped CFST members in axial compression performance were put forward.Finally,the research content and technical route of this paper were given.(2)The constitutive model of core concrete under uniaxial compression suitable for fiber element model analysis of concrete filled L-shaped steel tubular columns was proposed,and the fiber element model analysis method was expounded(Chapter 2).The loading path,loading assumption,calculation principle and calculation process of the fiber element model method were introduced.The existing test components were analyzed by the fiber element model method.The correctness of the fiber model was verified by comparing with the load-displacement curve of the test.(3)Considering the initial deflection of one thousandth of the member length,the mechanical properties of concrete filled L-shaped steel tubular column under axial compression were studied by using the fiber model program(Chapter 3).Based on the parameters of slenderness ratio,the yield strength of the steel,the compressive strength of the concrete,the depth to thickness ratio of steel tube and the depth to width ratio of the limb of the section,a large number of parameters of concrete-filled L-shaped steel tubular columns under axial compression were analyzed.On this basis,a simplified method for calculating the stability factor of concrete-filled L-shaped steel tubular columns under axial compression was proposed,and the formula was verified by the fiber model program.(4)Considering the initial eccentricity of one thousandth of the member length,the mechanical properties of concrete filled L-shaped steel tubular column under axial compression were studied by using the fiber model program(Chapter 4).When the initial eccentricity is on the asymmetric axis(X axis),due to the rotation of the neutral axis,the member will be subjected to biaxial eccentric compression.Compared with the results calculated by the formula proposed in Chapter 3,the stability bearing capacity will be reduced.Through a large number of parameter analysis,a simplified formula for calculating the reduction factor was proposed.The results of the formula were in good agreement with those of the fiber element model analysis.Finally,a modified simplified formula for calculating the stability bearing capacity of the concrete filled L-shaped steel tubular columns under axial compression was obtained.