This paper presents and discusses the available results of an ongoing investigation concerning the use of Generalized Beam Theory (GBT) to analyze the local, distortional and global buckling behavior of thin-walled steel frames with semi-rigid joints. Initially, an overview of the concepts and procedures involved in performing a GBT frame buckling analysis is provided, paying particular attention to the aspects related to ensuring displacement compatibility at the frame joints (between the end cross-sections of non-aligned members). Next, in a first attempt to simulate a frame joint semi-rigidity, linear spring elements, characterized by their stiffness values and relating the appropriate generalized displacements of the converging member end cross-sections, are incorporated into the buckling analysis. Finally, in order to illustrate the application and assess the merits of the above approach to modeling semi-rigid joints, numerical results concerning the buckling behavior of simple L-shaped and portal plane frames are presented and discussed. The frames analyzed (ⅰ) are formed by plain and lipped Ⅰ-section members, (ⅱ) are acted by loadings causing axial compression and in-plane (major-axis) bending, and (ⅲ) exhibit rotational springs at the joints, involving exclusively in-plane bending. The influence of the spring stiffness, which alters the member bending moment diagrams, on the frame buckling behavior (critical buckling load and mode nature) is investigated. For validation purposes, some GBT buckling results are compared with values obtained from ANSYS shell finite element analyses.
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