Research On Buckling Behavior Of Q460 Cold-Formed Thin-Walled Steel Lipped Channel Column Under Axial Compression

In current engineering,the cold-formed thin-walled specimens made of hot-plating aluminium-zinc high-strength steel are prone to buckling failure in the elastic stage due to the large width-thickness ratio,making it difficult to fully make the best of the material strength.However,traditional high-strength steel members are mostly welded,which are heavy and inconvenient to process.Therefore,this paper proposes a lipped channel specimen formed by cold bending of Q460 hot-rolling steel plate.Through experimental research and finite element numerical simulation,the mechanical behavior of such specimens under axial compression loads was explored,the influence of different geometric parameters on their load-carrying capacity was discussed,and a suggested formula suitable for distortional-local interaction buckling failure for Direct Strength Method(DSM)was proposed.The main research contents and conclusions are as follows:In terms of experimental research,axial compression tests were conducted on 16 pin-ended Q460 high-strength cold-formed thin-walled lipped channel columns with thicknesses of 4 mm and 6 mm.The buckling modes of specimens included global buckling,local buckling,distortional-global interaction buckling,and distortional-local interaction buckling.The ratio of the ultimate load to the full-section-yield strength(load-carrying efficiency)of them is mostly between 0.6 and 0.9,hence this type of specimen has a higher load-carrying efficiency.When the other dimensions remain,the effect of geometric parameters on the ultimate load-carrying capacity and efficiency of the specimen is basically manifested as follows:(i)with the increase of length,the slenderness ratio of the specimen increases,while the ultimate load-carrying capacity and efficiency both decrease,(ii)with the increase of web height,local buckling is more likely to occur,and the ultimate load-carrying capacity and efficiency firstly increase and then decrease,(iii)with the width of the flange increases,the constraint of the flange and lip combination on the web becomes stronger,so the load-carrying capacity increases,while its trend is related to the specimen length,(iv)with the thickness of the plate increases,the widthto-thickness ratio decreases,and the section stiffness increases,resulting in improved loadcarrying capacity and efficiency of the specimen.In terms of finite element analysis,a reliable finite element model was established and parametric analysis was carried out to explore the impact of initial geometrical imperfections and the effects of height-to-width ratio,lip width,plate thickness,specimen length and boundary conditions on the load-carrying performance.Research results show that:(i)different initial geometrical imperfections modes may lead to different buckling modes,which affect the load-carrying capacities,(ii)the initial geometrical imperfections amplitude only affects the load-carrying capacities,and the larger the initial geometrical imperfections amplitude,the lower the ultimate load-carrying capacity.Besides,(i)the increase in the aspect ratio of the section leads to changes in the buckling mode,which causes the ultimate load-carrying capacity and efficiency firstly increasing and then decreasing,(ii)the ultimate load-carrying capacity and efficiency are improved with the lip width or plate thickness increase,but its beneficial impact gradually indistinct,(iii)as the specimen length and slenderness ratio increases,the ultimate load-carrying capacity and efficiency decrease,with a gradual increase in the reduction range,and the failure mode also changes from distortional or local interaction buckling to global buckling,(iv)boundary conditions have a significant impact on the ultimate load-carrying capacity of global buckling,while the impact on the load-carrying capacity of distortional or local interaction buckling is not significant.In terms of design method research,by comparing the current Direct Strength Method(DSM)calculation formula with the load test results and finite element analysis results,it was found that the current calculation method was too conservative in predicting distortional-local interaction buckling load.The current distortional-local interaction buckling load formula is studied,and a revised recommended formula is given.Comparing the predicted values of the proposed formula and the original formula with the experimental and finite element data of distortional-local interaction buckling in this article,it is found that the calculated results of the proposed formula are in good agreement with the existing data results.Therefore,the research results of this article provide a reliable reference for improving the relevant design specifications of Q460 cold-formed thin-walled lipped channel,and contribute to promoting the application of such new types of specimens in engineering.