Possidente, Luca; Freddi, Fabio; Tondini, Nicola; (2023) Assessment of retrofit measures to prevent progressive collapse in steel structures. In: Proceedings of Conference Earthquake risk and engineering towards a resilient world (SECED 2023). Society for Earthquake and Civil Engineering Dynamics (SECED): Cambridge, UK.

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Abstract

Man-made hazards, such as fires, explosions, or impacts, may have severe social and economic consequences and, therefore, should be carefully considered during the design of new, as well as, during the retrofitting of existing structures. Among others, these events could induce the progressive collapse of structures, in which the localised failure spreads from the single affected structural component to other parts of the structure. It is important to highlight that most existing structures worldwide have been designed before the introduction of design rules against progressive collapse. Therefore, it is nowadays of paramount importance to identify effective retrofit measures to renovate existing structures and return safer buildings to the community, including explicit design considerations against progressive collapse. The present paper investigates the effectiveness of three different retrofit measures, namely roof-truss, bracing, and cable systems, conceived to increase the structural robustness and hence mitigate the progressive collapse risk in steel structures. A case study steel moment resisting frame (MRF) was studied by performing non-linear static analyses in OpenSees and investigating its response before and after retrofitting. The progressive collapse was simulated by considering central column loss scenarios, and the ability to prevent the spread of failures of the original and retrofitted structures was examined. The present study sheds some light on the effectiveness and limitations of the considered retrofit measures in improving the overall robustness of the frame. The results show that, after the column removal, the original configuration of the selected MRF fails due to column buckling. Therefore, only the roof-truss and bracings strategies effectively improve the frame’s robustness and allow the creation of alternative load paths. Additionally, some critical aspects to be carefully considered in the design of the retrofit measures are indicated.

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