Abstract
Effective length method is still widely used in engineering practice to evaluate the stability of compression members in frame structures. However, the conventional effective length method can be inaccurate in many cases as it considers columns in isolation from the stories above and below. This article proposes an improved method for simplified frame stability analysis that accounts for the vertical interaction effects of columns. The idealized sub-assemblage model includes the columns of all stories and their restraining beams. The stability matrix for a single-story unit is first derived, and then the system stability matrix is obtained by considering the compatibility of the story units. The governing equation for the elastic buckling load of the sub-assemblage is derived. The method is applicable to both sway-permitted and sway-prevented frames. The applicability and accuracy of the proposed method are demonstrated using a series of examples with a wide variation of parameters including numbers of story, boundary conditions, stiffness of beam-to-column connections, column length and stiffness, and axial force level.
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