Assessment of dynamic increase factor for progressive collapse analysis of RC structures

Assessment of a building vulnerability against progressive collapse using Nonlinear Dynamic (NLD) analysis has greater accuracy compared to other methods. Yet, the relevant standards and design guidelines allows the use of Linear Static (LS) analysis and Nonlinear Static (NLS) analysis to assess the progressive collapse risks of buildings. To approximately account for the dynamic effects due to sudden element removal, two different dynamic amplification factors namely, the Load Increase Factor (LIF) and the Dynamic Increase Factor (DIF) in linear and nonlinear static analyses, respectively are suggested. The DIF formulation of the current design guidelines of progressive collapse is relied on the material properties of the affected structural members. In this study, the effect of available structural capacity on DIF value in the Reinforced Concrete (RC) structures is investigated and on this basis a new empirical DIF formula is proposed. For this purpose, several three-dimensional RC building structures with different span lengths and number of stories are designed that have different levels of seismic resistance and implemented to derive the new DIF empirical formula. One of the advantages of the proposed formulae is the possibility of predicting stress and deformation in the RC structures' members after column removal.