Local and Distortional Buckling of Cold-Formed Steel Members

Laminar structures have a high post-buckling strength reserve. Cold-formed steel profiles can be taken as a set of thin plate elements. Therefore it is necessary to design this type of profiles taking into account that reserve of strength in post-local buckling modes of failure. The method normally used to design this type of structures is based on the Effective Width concept. The Effective Widths method, in addition to being highly empirical (giving little contribution to the understanding of the phenomena affecting the stability), leads to the application of a set of relatively complex calculations where the presence of human errors is not always easy to detect. The Direct Strength Method was developed in order to improve the speed and efficiency of the design of cold-formed profiles. This design method uses the buckling loads (for the Local, Distortional and Global modes) gathered from a computer-based analysis and experimentally calibrated resistance curves to predict the strength of the profile. Using the CUFSM software, a set of tables was created detailing the elastic buckling results (local and distortional) for a wide sample of commercially available profiles. Both Finite Strip Method (FSM) and Constrained Finite Strip Method (cFSM) were used. The objective of these tables was to create a tool to expedite the design of thin-walled profiles using the Direct-Strength Method (DSM). The automatic application of the MRD in lipped channel profiles was programmed using Matlab. This application was based on CUFSM source code and identifies the local and distortional modes on lipped channel profiles subject to (i) axial compressi used in order to find the global buckling loads. The created software uses these critical loads to calculate the resistance of the profile using AISI’s DSM In the last chapter the cold-formed related EC3 provisions are presented (EC3 example of its application on a lipped channel software Coldform was used to determine the buckling resistan compared with the ones resulting from a DSM analysis