Study On Mechanical Properties Of Circular And Hexagonal Concrete Filled Steel Tubular Columns Under Long-term Loads Effect

In recent years,the concrete-filled steel tubular composite structure has been widely used in high-rise,large-span and bridge structures due to its high bearing capacity,good ductility and convenient construction.Round-end and hexagonal concrete-filled steel tubes have also been used in engineering practice due to their good external shape and force characteristics,and have broad application prospects.The long-term load has great influence on the internal force distribution,deformation,bearing capacity and other mechanical properties of round-end and hexagonal CFST members.This paper uses finite element software to consider the effect of long-term load on round-end steel tube concrete and six.The working mechanism of the axial compression and biasing members of the square-shaped concrete filled steel tube is analyzed,and the practical calculation method of the bearing capacity is proposed based on the parameter analysis.The main work and achievements are as follows:?1?On the basis of selecting the appropriate material constitutive structure,the finite element software is used to nonlinearly analyze the round-end steel tube concrete and the hexagonal steel tube concrete member,and the axial pressure of the round-end and hexagonal members is established.The finite element model of the bias and the finite element model of the circular and rectangular CFST members considering the effects of long-term loads are used to verify the accuracy of the finite element model.?2?On the basis of the above finite element model,the whole process working mechanism of the round-ended steel tube concrete and hexagonal concrete-filled steel tubular axial members considering the influence of long-term load is analyzed.The results of mechanism analysis show that the peak load of the circular-shaped and hexagonal CFST columns is reduced when the long-term load is considered,but the reduction is not significant and the peak strain is significantly increased.?3?The whole process working mechanism analysis of round-end steel tube concrete and hexagonal steel tube concrete biasing members considering the influence of long-term load is carried out,and the bias loading method?including strong shaft bias and weak shaft bias?is investigated.The effects of factors such as load eccentricity and cross-sectional aspect ratio on the component.The results of mechanism analysis show that the stiffness and peak load of the round-shaped and hexagonal concrete-filled steel tube columns is significantly reduced and the peak strain is significantly increased.The binding force of the round-ended steel tube concrete is mainly concentrated in the circle.The arc,hexagonal steel tube concrete binding force is mainly concentrated in the corner.?4?Parameter analysis is carried out on the influence coefficient k_crr of the round-end and hexagonal concrete-filled steel tubular members under the influence of long-term effects.The parameter analysis results show the parameters such as slenderness ratio,concrete strength,steel content and load eccentricity.It has a greater impact on its k_cr.On the basis of parameter analysis,the practical calculation table of k_cr of round-end and hexagonal CFRP members considering the influence of long-term load is calculated and the practical simplified calculation formula of k_cr is summarized.Simplified calculation results are in good agreement with numerical calculation results.