Research On Distortional Buckling Of Cold-formed Thin-walled Lipped Channel Steel Under Pure Bending Around Minor Axis

Due to the small thickness and large width-to-thickness ratio of coldformed thin-walled lipped channel steel members,the stability of such members is a key factor to control the ultimate load.Under external loads,lipped channel steel members may be damaged due to distortional buckling,local buckling or global buckling.As a special buckling mode different from local buckling and global buckling,distortional buckling may play a key role under certain conditions.At present,the research on the distortional buckling performance of axial compression members or pure bending members around major axis has been relatively perfect,while the distortional buckling performance of pure bending members around minor axis needs to be further studied.Therefore,in this paper,the distortional buckling performance of lipped channel steel members under bending moment around minor axis is studied and analyzed by combining theoretical analysis with finite element and finite strip software.Because the distortional buckling performance will vary with the change of the bending angle of the edge,this study selects the straight edged and oblique edged channel steel members as the research object,and studies the distortional buckling performance of them around the minor axis.(1)The elastic distortional buckling stress of channel steel members with pure bending around the minor axis can be solved by the finite strip software CUFSM,and then the influence of various scale parameters on the distortional buckling stress can be studied.On this basis,the calculation formula for solving the elastic distortional buckling critical stress of straight curling members and oblique curling members can be established.The section forms of different scale parameter ranges are selected as the research object,and the elastic distortional buckling stress is calculated by the simplified formula and the finite strip program respectively.After comparing the calculation results of the two methods,it is found that the results obtained by the simplified formula are more accurate and can meet the calculation requirements of designers.(2)The finite element software ANSYS was used to analyze the distortional buckling performance and ultimate load of a large number of straight edged and inclined edged channel steel members with pure bending around the minor axis.The influence of different section geometric parameters on the failure mode and ultimate load of the members is discussed.The results show that different section parameters have a certain influence on the ultimate load,and the thickness of the plate and the width of the edge are the key factors affecting the distortional buckling performance.(3)Based on the study of straight edged and inclined edged channel steel members under pure bending around the minor axis,the original calculation formula of direct strength method for pure bending members is modified so that it can be applied to solve the ultimate load of straight edged and inclined edged channel steel members under bending around the minor axis.The modified formula is used to verify the applicability of the DSM calculation formula of the eccentric compression members to the eccentric compression members around the minor axis.The results show that the modified direct strength method of pure bending members has little difference with the finite element analysis results,and The DSM calculation formula of eccentric compression members only has high accuracy for members with small eccentricity.