Ma, TerenceXu, Lei2021-06-082021-06-082021-01https://doi.org/10.1061/(ASCE)ST.1943-541X.0002874http://hdl.handle.net/10012/17095A simplified method is proposed for evaluating the stability of multi-storey, steel semi-braced and unbraced frames with semi-rigid connections. The proposed method decomposes a frame into individual storeys and evaluates the lateral stiffness of each storey via the storey-based stability approach with explicit, closed form solutions. Lateral sway instability occurs when the lateral stiffness of any storey diminishes to zero, and the storey for which this occurs can be considered the weakest storey in the frame. The results of the proposed method are theoretically verified via comparison to the results of finite element analyses. Use of the proposed decomposition method requires assuming the buckled shape of the frame, which is shown to provide satisfactory approximations of critical loads for engineering practice. Parametric studies are conducted to assess the sensitivity of the results to the corresponding buckling shape parameters. The assumption of asymmetric buckling, which is generally consistent with the sway buckling mode in semi-braced frames, produces reliable results in the proposed decomposition method.enstabilitysteel framesmultistoreyproportional loadingswaybucklingstorey-basedArticle