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Steel and Composite Structures
  Volume 25, Number 5, December10 2017 , pages 617-624

Dynamic Increase factor based on residual strength to assess progressive collapse
Javad Mashhadia and Hamed Saffari

    In this study, a new empirical method is presented to obtain Dynamic Increase Factor (DIF) in nonlinear static analysis of structures against sudden removal of a gravity load-bearing element. In this method, DIF is defined as a function of minimum ratio of difference between maximum moment capacity (Mu) and moment demand (Md) to plastic moment capacity (Mp) under unamplified gravity loads of elements. This function determines the residual strength of a damaged building before amplified gravity loads. For each column removal location, a nonlinear dynamic analysis and a step-by-step nonlinear static analysis are carried out and the modified empirical DIF formulas are derived, which correspond to the ratio min of beams in the bays immediately adjacent to the removed column, and at all floors above it. Therefore, the new DIF can be used with nonlinear static analysis instead of nonlinear dynamic analysis to assess the progressive collapse potential of a moment frame structure. The proposed DIF formulas can estimate the real residual strength of a structure based on critical member.
Key Words
    progressive collapse; nonlinear static analysis; dynamic increase factor; alternate load path; residual strength
Javad Mashhadia and Hamed Saffari: Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, 22 Bahman Blvd. P.O. Box 76175-133, Kerman, Iran

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