Modification of dynamic increase factor to assess progressive collapse potential of structures

Progressive collapse assessment of buildings against column removal requires a time consuming nonlinear dynamic analysis therefore nonlinear static analysis considering a proper dynamic increase factor (DIF) can be utilized as an alternate analysis to predict maximum dynamic response of structures. In this study, the effect of post-elastic stiffness ratio of members on DIF in nonlinear static analysis of structures against column removal is investigated, and a modified empirical DIF is presented. For this purpose, series of low and mid-rise moment frame structures with different span lengths and number of stories are analyzed. For each ratio of post elastic stiffness, a non-linear dynamic analysis and a step-by-step nonlinear static analysis are carried out. The results of analysis reveal post-elastic stiffness ratio is an efficient parameter on DIF. Therefore the new empirical formulas including moment demand, ductility and post-elastic stiffness ratio are suggested. Finally, it is shown that the proposed DIF formulas are accurate and efficient.