Buckling Behavior And Failure Mode Identification Of Cold-formed Steel Omega Column

In recent years,in order to adapt to the rapid development of logistics and e-commerce in China.As the main load-bearing structure of warehouse,the light-weight,high-strength and quick installation of cold-formed steel rack are widely used in the field of logistics and warehouse.The columns in cold-formed steel rack generally adopt Omega open section,which is formed by bending many times,the buckling behavior of columns is complex and the failure mode identification is difficult.The existing studies show that the bearing capacity of cold-formed steel members is closely related to their buckling behavior.In this paper,the buckling behavior and failure mode of cold-formed steel Omega columns are deeply studied to provide theoretical basis and technical support for accurately predicting the buckling bearing capacity of such members.In this paper,firstly,based on the c FSM(constrained finite strip method)and the idea of one-dimensional modal spectra method,a more efficient modal identification based on one-dimensional modal spectra(MID-1D Spectra)for shell element nonlinear finite element model is proposed;then parametric analysis of cold-formed steel Omega column under axial compression is carried out,and the modal identification based on one-dimensional modal spectra is used to quantitatively identify failure mode of members,correlation analysis and regression analysis were used to investigate the influence of Omega column geometric properties on the participation of various buckling modes(global buckling,distortional buckling,local buckling and other buckling)in the failure mode;secondly,according to the results of parametric analysis,dimension of Omega column geometric properties are reduced by factor analysis method,and common factors are extracted,the multiple linear regression analysis method is used to establish the slenderness ratio interval model of cold formed steel Omega column with single "pure" buckling mode;finally,the fast prediction model(FPM)of failure mode of cold formed steel Omega column is established by using the multi classification logistic regression analysis method.The main conclusions are as follows:(1)modal identification based on one-dimensional modal spectra(MID-1D Spectra)for shell element nonlinear finite element model can accurately identify the buckling modes of members,the results are consistent with the modal identification based on three-dimensional base mode(MID-3D Mode).And when the shell element model is same,The calculation time of MID-1D Spectra is about 28% of MID-3D Mode.By reducing the number of pure buckling modes involved in the fitting,under the condition that the results of modal identification are consistent,the calculation time of MID-1D Spectra can be about 1% of MID-3D Mode,calculation efficiency of modal identification is greatly improved.(2)Slenderness ratio has a great influence on the failure mode of axial compression Omega column.When the slenderness ratio is small,the failure mode is only local buckling;when the slenderness ratio is medium,the failure mode is only distortional buckling;when the slenderness ratio is large,the failure mode is only global buckling.Within a certain slenderness ratio,the failure mode of the member is only a single buckling mode,while in other slenderness ratio regions,the failure mode of the axial compression Omega column is various related buckling modes.(3)Section geometry also has a great influence on the failure mode of the axial compression Omega column,and the influence on the participation of buckling modes is different under different slenderness ratio.When the slenderness ratio is small,the failure mode is mainly affected by plate width-thickness ratio and lip width-thickness ratio,with the increase of plate width-thickness ratio and lip width-thickness ratio,the local buckling participation increases and the distortional buckling participation decreases in failure mode;when the slenderness ratio is large,the failure mode is mainly affected by ratio of lip width to section width and section height-width ratio,with the increase of ratio of lip width to section width and section height-width ratio,the global buckling participation increases and the distortional buckling participation decreases in failure mode.(4)Based on the influence of section geometric properties on Omega column failure modes under different slenderness ratios,taking section geometric properties as variables and upper and lower limits of slenderness ratio interval of single buckling mode as dependent variables,an interval regression model of slenderness ratio for local buckling,distortional buckling and global buckling of Omega columns under axial compression is established.Through the model,it can be seen that the slenderness ratio range of global buckling and distortional buckling is greatly affected by lip size and plate size,and the slenderness ratio interval of local buckling is greatly affected by the thickness and plate size.(5)Based on the influence of geometric properties and slenderness ratio of axial compression Omega column on its failure mode,taking section geometric properties and slenderness ratio as variables and failure mode as dependent variables,a failure mode fast prediction model based on logistic regression model of Omega columns under axial compression is established.According to the geometric properties and slenderness ratio,the probability of seven failure modes(global buckling,distortional buckling,local buckling,global-local correlation buckling,global-distortional related buckling,local-distortional related buckling,global-local-distortional related buckling)can be predicted quickly.Compared with the test results,the prediction method can accurately judge the failure mode.