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 mridified 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. (C) 2017 Elsevier Ltd. All rights reserved.