| Elliptical concrete filled double skin steel tubes column is a composite member with a new cross-section.Elliptical section has many advantages in terms of functionality and aesthetics.It not only has a streamlined appearance,but also combines the advantages of a circular cross-section and a square cross-section.It has a better restraining force similar to a circular section,while avoiding the problem of stress concentration at the corners of the square section.In addition,the difference in lateral stiffness between the long axis and the short axis of the component can not only meet the stress requirements in the main stress direction of the structure,but also save the material consumption in the other direction.Elliptical concrete filled double skin steel tubes structure replaces the concrete near the concrete centroid with the inner steel tube,which reduces the self-weight of the structure,improves the bending stiffness of the component,and ensures the bearing capacity of the component.At present,there are still few studies on elliptical concrete filled double skin steel tubes columns at home and abroad,and most of them focus on circular and square cross-section.The lack of systematic research on the force of elliptical concrete filled double skin steel tubes members seriously restricts its application and development.In this paper,the axial compression performance and eccentric compression performance of elliptical concrete filled double skin steel tubes members are tested and analyzed by finite element method,which lays a foundation for promoting the application of this member in practical engineering.The work is as follows:(1)Axial compression tests of eight elliptical concrete filled steel tube short columns were carried out,including two elliptical concrete filled steel tube solid short columns and six elliptical concrete filled double skin steel tubes short columns.The main test parameters are hollow ratio,steel strength and concrete strength.The failure mode and force mechanism of the new composite member are revealed.The load-displacement curve,strain response of whole loading process,ductility index,concrete contribution rate and bearing rapacity to weight ratio of elliptical concrete filled double skin steel tubes short column under axial compression are studied.The results show that the main failure mode of short columns is the ring drum failure accompanied by shear failure.The mechanical properties of short columns under different parameters are not alike and the elliptical concrete filled steel tube short columns have the characteristics of lightweight and high strength,better practicability and economic benefits compared with the elliptical concrete filled steel tubu short columns with the same parameters.(2)The finite element analysis method is used to analyze the axial compression mechanical properties of elliptical concrete filled double skin steel tubes short column.The finite element model of axial compression member consistent with the test was established,and its failure mode,ultimate bearing capacity,load-displacement curve and axial compression test results were compared.On the basis of ensuring the accuracy of the finite element model in this chapter,the influence of engineering application,material parameters and geometric parameters on the axial compression mechanical properties of elliptical concrete filled double skin steel tubes columns is fully considered.The stress state of elliptical concrete filled double skin steel tubes axial compression short column under different parameters is further studied and the stress mechanism is analyzed.(3)Eccentric compression tests of eight elliptical concrete filled double skin steel tubes short columns were carried out.The main test parameters are eccentric direction,eccentricity,steel strength and concrete strength.The failure mode and force mechanism of the new composite member are revealed.The load-displacement curve,strain response of whole loading process,ductility index and strength index of elliptical concrete filled double skin steel tubes short column under axial compression are studied.The results show that the main failure mode of short columns is the ring drum occurs on the eccentric side of the short column,and the opposite side of the short column is stretched.The mechanical properties of short columns under different parameters are not alike.Compared with the axial compression short column with the same parameters,the eccentric compression short columns with elliptical concrete filled double skin steel tubes have lower bearing capacity,but the ductility index is generally higher.(4)The finite element analysis method is used to analyze the eccentric compression mechanical properties of elliptical concrete filled double skin steel tubes short column.The finite element model of eccentric compression member consistent with the test was established,and its failure mode,ultimate bearing capacity,load-displacement curve and eccentric compression test results were compared.On the basis of ensuring the accuracy of the finite element model in this chapter,the influence of engineering application,material parameters and geometric parameters on the eccentric compression mechanical properties of elliptical concrete filled double skin steel tubes columns is fully considered.The stress state of elliptical concrete filled double skin steel tubes eccentric compression short column under different parameters is further studied and the stress mechanism is analyzed.(5)Based on the code and related research results,a simplified calculation formula for axial compression bearing capacity and eccentric compression bearing capacity of elliptical concrete filled double skin steel tubes short columns is proposed.The accuracy of the calculation results of the two formulas is verified by the test results and the finite element analysis results.The results show that the bearing capacity calculation formula proposed in this paper has good applicability for the axial compression and eccentric compression bearing capacity of elliptical concrete filled double skin steel tubes short columns. |
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