Imperfection Sensitivity Analysis Of Cold-formed Thin-walled Columns Experiencing Local-distortional Interaction

In recent years,cold-formed thin-walled steel has been widely used in the field of prefabricated building structures due to its advantages of light weight,high strength and excellent seismic resistance.Due to the thin section thickness of the member itself,initial imperfection（including residual stresses and initial geometric imperfections）will inevitably occur in the process of production,transportation and installation.The existence of these initial imperfections will greatly reduce the load-carrying capacity of cold-formed thin-walled steel members.Therefore,it is important to study the initial imperfection of cold-formed thin-walled steel members in promoting the application of cold-formed thin-walled steel structures.In this work,a new imperfection simulation method was proposed to reasonably consider the inevitable initial imperfection in the finite element analysis of cold-formed thin-walled components.By using the proposed imperfection simulation method,the finite element modeling and initial imperfection consideration were carried out for the available cold-formed thin-walled steel columns（including 40 web-stiffened lipped channel cold-formed steel columns and 10 C-section columns）experiencing local-distortional interaction buckling failure,and the load-carrying capacity of these cold-formed steel columns were obtained using finite element analysis.The finite element analysis results were compared with the experimental data to verify the accuracy of the proposed imperfection simulation method.Then,the geometrics of 224 web-stiffened lipped channel cold-formed steel columns and 210 C-section columns affected by local-distortional interaction buckling were determined using constrained finite strip method,and these members were adopted as research objects in this paper.Moreover,using the proposed imperfection simulation method,the load-carrying capacity(P_num)of each cold-formed thin-walled steel column with the inevitably initial imperfection was calculated.Next,different initial geometric imperfections were introduced into these cold-formed thin-walled steel columns,and the ultimate capacity of each member with various imperfections(P_imp)were obtained with the help of finite element analysis,and the ultimate capacity of each member under the influence of various imperfections were compared with its counterpart of the member has inevitable initial imperfections(P_num),and thus the influence of various imperfections on the load-carrying capacity of the member were obtained,respectively.Finally,using the most widely used design method of cold-formed thin-walled steel components-direct strength method,the load-carrying capacity predictions(P_DSM)of these members were obtained respectively.Comparing the load-carrying capacity predictions of the members with the load-carrying capacity P_num of these members with inevitable initial imperfection,the direct strength methods assessments were conducted.Through the research,this work finally concludes that:（1）The imperfection simulation method proposed in this paper is suitable for calculating the load-carrying capacity of web-stiffened lipped channel and C-shaped cold-formed steel columns with local-distortional interaction buckling failure;（2）The symmetric distortional buckling type imperfection with odd number of buckling half-wavelength has a great impact on the load-carrying capacity of the cold-formed thin-walled components experiencing local-distortional interaction buckling failure;In addition,not all initial imperfection will reduce the load-carrying capacity of the members,and some geometric imperfection will even increase the ultimate capacity of the members;（3）Although the calculation accuracy of the existing direct strength methods for the local-distortional interaction buckling failure is different,they can all meet the reliability design requirements of compressive cold-formed thin-walled components.The conclusions of this paper can provide suggestions for the design and production of cold-formed thin-walled steel members and the optimization of the relevant direct strength methods.