Story-Based Stability of Multistory Steel Semibraced and Unbraced Frames with Semirigid Connections

Abstract

A simplified method is proposed for evaluating the stability of multistory, steel, semibraced, and unbraced frames with semirigid connections. The proposed method decomposes a frame into individual stories and evaluates the lateral stiffness of each story via the story-based stability approach with explicit, closed-form solutions. Lateral sway instability occurs when the lateral stiffness of any story diminishes to zero, and the story for which this occurs can be considered the weakest story in the frame. The results of the proposed method are theoretically verified via comparison to the results of finite-element analyses. The 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 semibraced frames, produces reliable results in the proposed decomposition method.