Study On Local Buckling Mechanical Behavior Of Cold-Formed Circular Steel Tubes Based On High-Fidelity Finite Element Model

Cold-formed circular hollow sections（CHS）steel tubes have excellent mechanical properties such as high strength and good ductility,often used as load-bearing columns in buildings.With the improvement of manufacturing level,high strength(f_sy≥460MPa)CHS has also been rapidly applied to the construction.At present,the world is still in a period of earthquakes active,and columns are prone to local buckling under the earthquake,which seriously threatens the safety of the structure.In order to study the mechanical properties of structural columns under strong earthquakes,the study of the local buckling mechanical behavior of cold-formed CHS steel is an urgent work project.In this paper,the research objective of this paper is cold-formed CHS steel,through theoretical analysis,correlation analysis and numerical simulation,the main work and research results are as follows:（1）The uniaxial tensile engineering stress-strain curve of cold-formed CHS steel is established.Compared with hot-rolled steel,the uniaxial tensile stress-strain curve of cold-formed steel usually has no obvious yield point,and the yield stage is more smooth.A total of 84 tensile coupon experimental data were collected,and these specimens were taken from cold-formed CHS.Based on the Menegotto-Point function and basic mechanical parameters of the virgin steel,the sensitivity analysis and correlation analysis are carried out.The prediction expression of key mechanical indexes such as yield strength f_sy,ultimate strength f_su,and corresponding strain after cold bending is determined one by one.By comparing with the measured results,the accuracy of the stress-strain model is verified.（2）A numerical model of cold-formed CHS steel stub columns under axial compression was established.The numerical model of cold-formed CHS steel stub columns under axial compression was established by the finite element software ABAQUS,which fully considers the material nonlinearity and geometric nonlinearity.The local buckling modes and load-deformation curves obtained by numerical simulation are basically consistent with the experimental results,which verifies the feasiblity and accuracy of the model.The established numerical model can be further used for the numerical simulation of cold-formed circular steel tube members.The established model can be further used for the numerical simulation.（3）The local buckling mechanical behavior of high-strength circular steel tubes was systematically analyzed.Based on the verified numerical model,the parametric analysis is carried out to study the local buckling modes,buckling strength,and section capacity of high-strength circular steel tubes under different section types.The results show that the high-strength circular steel tube with a yield strength above 800 MPa mainly occurs an elephant foot at the end of the columns.When the general diameter-to-thickness ratio is the same,increasing the yield strengthof the material can improve the ductility and stability of the component,combined with the relationship between local buckling and buckling load of different section types of circular steel tubes,the calculation formula of buckling strength is proposed from the perspective of design safety.（4）A method for the upper limit of the diameter-to-thickness ratio of high-strength circular steel tubes section is proposed and compared with the current mainstream steel structural design codes.The results show that the upper limit of Eurocode 3 is the most conservative,and the upper limit of GB50017-2017 is slightly conservative.Based on the research results,the upper limit value of the diameter-to-thickness ratio of a high-strength circular steel tube section is relaxed on the basis design code.