Influence of imperfections on the progressive collapse of steel moment resisting frames

The performance of steel moment resisting frames with sway imperfections is numerically studied in this paper, under various sudden column removal scenarios. The response of 2D frames with varying values of sway imperfection is comparatively examined against respective perfect frames, under both nonlinear static and time history analyses. In this context, the study also investigates the role of frame design, working with two groups of alternatively designed frames: the first one governed by earthquake loading and the second governed by wind loading. Furthermore, some additional variables to the study are introduced. These are the number of frame storeys, the location of the removed column and the duration of the column removal. The obtained results reveal that the imperfect frames, depending on the location of the removed column, can deteriorate in terms of ductility, reaching increased column demands, compared to the perfect ones.