Effect of damping ratio and hardening on the Dynamic Increase Factor for a column loss hazard

Accidental actions like bomb blasts, gas explosions or car collisions are severe hazards that can pose a structure to extreme demands and potentially lead to collapse. To cope with these actions and avoid undesirable failures, indirect or direct design methods could be implemented. The alternate path method (ALP) has been a particularly popular direct design method among designers and researchers as it can efficiently study the capability of a structure to redistribute the loads under a column loss scenario in a computer-based environment. The application of this method is mostly efficient with static analyses rather than dynamic due to the smaller degree of modelling and analysis complexities associated with them; however, their use would necessitate the consideration of a Dynamic Increase Factor (DIF). Traditional standards such as the Unified Facility Criteria (UFC) for progressive collapse of buildings, propose DIFs that are based on ductility. The effect of other important parameters such as hardening or damping ratio is not explicitly captured by these provisions. This paper aims to highlight the distinct effect of these parameters and compare it with the UFC provisions and other recommendations in the literature. For this purpose, an analytical methodology based on a nonlinear SDOF system which accounts for these factors is used for the estimation of the DIFs. The results presented in this work demonstrate the important effect of both damping ratio and hardening on the DIF and how different predictive models compare to each other depending on the size these factors attain.