Study On Stability Of Cold-formed Thin-walled Flanged Channel Column With Web Holes

In order to facilitate the passage of life auxiliary facilities in light steel structures,holes are opened on the web of cold-formed thin wall steel members.Due to factors such as hole,thin wall,large ratio of width to thickness and complex section form,buckling instability of members is easy to occur.Buckling modes consists of three types: global buckling,distortion buckling and local buckling,which often occur between the two or even three coupled buckling modes,coupling effect affects the ultimate bearing capacity and stability of members.Based on the direct strength method,a new idea for calculating the stability bearing capacity of cold-formed thin-walled steel members under axial compression is presented in this paper.The calculation method of stability bearing capacity includes effective width method and direct strength method.The direct strength method is directly calculated according to the full section characteristic,considering the effect of local buckling,and taking the distortion buckling mode as an independent influence factor into consideration,greatly simplifying the calculation process and making up for the deficiency of the effective width method.In this paper,compression tests were conducted on 30 short and intermediate length cold-formed thin-walled columns with or without web holes,the stability bearing capacity,load-displacement curve,displacement of the web and flange were measured and observed the deformation.C1 cold-formed thin wall stub columns with holes failing by distortional-global instability interaction,C2 cold-formed thin wall stub columns with holes failing by distortional-local instability interaction,C1 cold-formed thin wall intermediate length columns with holes failing by global instability.Test results show that the stability bearing capacity and buckling mode of 30 specimens are affected by parameters such as length,width-to-thickness ratio of plate,edge curl,holes and the diameter of circular holes.In this paper,30 specimens are also simulated by finite element method.Through a detailed comparison with test results,it is proved that finite element model can simulate actual force of specimens better.The existence of holes affects the stability bearing capacity and buckling mode of cold-formed thin-walled columns.A simplified calculation method to consider the influence of holes has been proposed in the past.The critical force of elastic buckling is calculated by weighted average section characteristics and modified finite strip models.A large number of experimental data and finite element simulation results reveal how holes and boundary conditions affect distortional buckling and local-global correlation buckling.In inelastic state,the net section becomes a weak section limiting the ultimate bearing capacity.Six correction schemes for the Direct Strength Method(DSM)are proposed.At present,a simplified method based on approximate model is used to calculate elastic buckling parameters of cold-formed thin-walled members with holes,which affects the accuracy of elastic buckling parameters and the stable bearing capacity.In order to improve the accuracy of the stability bearing capacity,it is necessary to elaborate the elastic buckling parameter analysis of the model.A buckling mode recognition method based on the hypothetical force features provides necessary conditions.On the other hand,six correction schemes of the Direct Strength method(DSM)are calculated and compared to determine the most effective scheme,which aims to improve the accuracy of the calculation of stability bearing capacity.