Study On The Compression Stability Of Built-up Cold-formed Steel Special-shaped Tube

With the rapid development of cold-formed steel,new types of combined sections are emerging and further study is required on their stability performance.This paper adopts the finite element software to study the stability performances of a new type of built-up cold-formed steel special-shaped tube proposed by Technical standard for assembly elevator-adding building with cold-formed steel structures T/CSCS 010 under the circumstances of axial compression and eccentric compression.Based on that,a calculation method for the stability bearing capacity is proposed.In order to verify the reliability and accuracy of using the finite element method to analyze such problems,the finite element modeling parameters and the initial defect consideration method were discussed and modified with the existing experimental data for cold-formed steel compression members with bonded sections,so as to ensure the credibility of the analysis results.Parametric analysis was carried out for the axial compression stability of the built-up cold-formed steel special-shaped tube.The parameters included slenderness ratio,initial bending,bolt spacing,cold bending effect and residual stress.A total of 275 finite element specimens were considered.The results of the analysis showed that the slenderness ratio of the components not only had a significant impact on the ultimate bearing capacity,but also on the instability of the form.The initial bending can also significantly reduce the ultimate bearing capacity,and the influence is related to the slenderness ratio of the component.The influence of bolt spacing,cold bending effect and residual stress on the ultimate bearing capacity is small.Parametric analysis was also carried out for the compression-bending stability of the built-up cold-formed steel special-shaped tube.The parameters included slenderness ratio,eccentricity,eccentricity direction,cold bending effect and residual stress.A total of 210 finite element specimens were considered.The results of the analysis showed that the failure of compression-bending members was affected by the section size and eccentric direction.Eccentricity and slenderness ratio have adverse effects on the ultimate bearing capacity and stiffness of the members.The cold bending effect and residual stress have little effect on the bearing capacity of the components,and have a favorable effect under large eccentricity.The stability bearing capacity of the finite element specimens was calculated using the methods specified by Chinese GB50018 and American AISI.The results were compared with the stability bearing capacity obtained by finite element analysis.The results showed that,except for a few specimens,the design is safe according to the current Chinese and American specifications.According to the results of the finite element analysis,the relevant parameters are adjusted and modified based on the formula recommended by the current code in China,and suitable methods are proposed to calculate the axial compression and compression-bending stability bearing capacity of the built-up cold-formed steel tubes.These results can be used as a reference by engineering and technical personnel.