EFFECT OF GEOMETRICAL IMPERFECTION ON ANALYTICAL BUCKLING STRENGTH OF COLD-FORMED LIPPED CHANNEL STEEL MEMBER UNDER COMPRESSION

Thin waled cold-formed steel member is manufactured by cold-forming a galvanized steel sheet of less than 2.3 mm. It is possible to manufacture a variety of cross-sectional shapes with less expensive manufacturing equipment than the conventional hot rolling process. This thin waled cold-formed steel member allows for greater customization (different web, flange and lip width) that can cater for many industrial applications of flooring, roofing, or modular building systems. In this thin waled cold-formed steel members, since the width-to-thickness ratio of the plate elements that make up the cross-section is large, local buckling is likely to occur at the plate elements before the maximum strength is reached. In addition, since a unique buckling mode called distortional buckling that includes the collapse of the cross-section is occurred, one of the important research subjects is to analyze the buckling behavior in detail and to establish a quantitative evaluation method of member strength. Numerical analysis by the finite element method is a useful tool for analyzing the complex buckling behavior of thin waled cold-formed steel members. However, regarding the validity of buckling behavior combined with eigenvalue analysis, there are very few studies that analyzed in detail the effect of changes in initial imperfections on the analysis results, and it is necessary to clarify the application range of the method that introduces the initial imperfections based on the eigenvalue analysis results. In this paper, the effect of initial imperfections in the finite element analysis on the buckling behavior of cold-formed lipped channel steel member is investigated. Firstly, the buckling behavior and its buckling mode are clarified by stub column tests. Then, the effect of the differences in the shape of the initial imperfections in finite element analysis is investigated. From the stub column tests, the following are found. 1) In the case of a cross-section that satisfies the required lip width and the maximum strength is determined by local buckling, the maximum strength can be evaluated by accumulating the maximum strength of each plate element. On the other hand, in the case of a cross-section that does not satisfy the required lip width, the maximum strength determined by local buckling cannot be evaluated by this method. 2) Based on the DSM, the local bucling and the distorsional buckling strength are evaluated on the safe side. Also, the coupled buckling strength, w