Local And Distortional Coupled Buckling Analysis Of Cold-formed Thin-walled Lipped Channel Steel With Stiffeners Under Axial Compression

With the development of cold-formed thin-walled steel,more and more channel steels with middle stiffeners are widely used in industrial buildings.Due to the influence of stiffeners,distortional buckling plays an increasingly important role in the failure modes of components.In order to study the effect of stiffener type and size on local and distortional coupling buckling of cold-formed thin-walled channel steel column in axial compression,in this paper,four sections channel steel column without stiffeners,webs with stiffeners,flange with stiffeners,webs with stiffeners and flange with stiffeners are used to carry out axial compression test research,and the software abaqus is used to analyse.In order to explore the influence of initial defects on the test results,the bearing capacity of specimens was calculated based on the Chinese and American specifications for cold-formed thin-walled steel,and the applicability of the calculation formula for cold-formed thin-walled lipped channel steel with stiffeners was explored.Primary contents are as follows:(1)The influence of different stiffeners on the ultimate bearing capacity and failure modes was studied through the axial compression test of 24 channel steel columns.From the test results,it can be seen that the ultimate load of the specimens with stiffeners is increased compared with those without stiffeners.The anti-buckling effect of web with stiffeners,web and flange with stiffeners are obvious,the failure mode of the compression bars change from local buckling to local distortional coupled buckling and distortional buckling mode.As for the bearing capacity,the D section is the most effective to improve the bearing capacity.(2)Several calculation methods for calculating the ultimate buckling capacity of cold-formed thin-walled steel with distortional buckling are introduced and the calculated results are compared with the experimental results.For most specimens,according to Lau’s and Hancock’s methods,the calculated results of the compressive bar’s distortional buckling capacity are smaller than the test value,so the method is too conservative.The reason is that Lau and Hancock did not consider the post-buckling strength of the distortional buckling.The error of Kwon and Hancock’s calculation method for A section is relatively small,and the calculation results are reasonable.The calculated values of other specimens are all less than the test values.Because the material in this test is not high-strength steel and does not have large post-buckling strength,this formula is not applicable.The calculated results of Schafer direct strength D formula are all larger than the experimental values,which are conservative and safe.(3)The finite element software ABAQUS was used to model and calculate the test specimen,and the influence of the initial defects on the bearing capacity was discussed.The parametric analysis is carried out and the conclusion is drawn: For the specimen with local buckling,the errors of applying the first and second order modes are the smallest,and the errors of applying only the first order mode are the largest.Thicknesses have significant effects on local buckling 、 local-distortional coupled buckling,and ultimate bearing capacity of distortional buckling.The thicker the specimen,the greater the ultimate bearing capacity of the specimen.With the increase of the thickness,the local buckling phenomenon of the specimen gradually disappeared.The influence of stiffener dimension on buckling performance is analyzed by finite element method.The calculation results show that when the ratio of the depth of the web stiffener to the width of the flange is about 0.12,and the ratio of the width of the stiffener to the width of the web is about 0.2,the buckling capacity of the thin-walled lipped steel increases the most,and the distortional buckling mainly occurs.(4)The bearing capacity of the test specimens in this paper and in the literature is calculated by using the Chinese and American cold-formed thin-walled steel specifications,and the applicability,difference and accuracy of the codes for the bearing capacity of cold-formed thin-walled steel specimens with stiffeners are analyzed.For the specimens of cold-formed thin-walled channel columns with stiffeners,the effective width method in the specifications of China is still conservative,and the calculation result is smaller than that in the American specifications,and the performance of the material needs to be further used.Finally,through regression analysis by Matlab,the formula for calculating the stability coefficient K of the plate with intermediate stiffener is obtained,and the fitting effect is good.