ASSESSMENT AND RETROFITTING OF A RC BUILDING THROUGH A MULTI-HAZARD APPROACH: SEISMIC RESISTANCE AND ROBUSTNESS

Most of the existing buildings in seismic prone regions have been built before the publication of modern design provisions against seismic events and progressive collapse. Nonetheless, some studies have highlighted the possible interaction between earthquake resistance and structural robustness, the latter being of interest to either individual extreme hazards (e.g., blast, impact, fire) or interacting hazards (e.g., landslides produced by seismic events). While retrofit strategies to improve the seismic performance of reinforced concrete (RC) structures have been widely investigated since many years, the topic of mitigation strategies against progressive collapse received very little attention. Progressive collapse can be described as a special type of structural collapse that involves several components of the structure as consequence of an initial localised damage. The present study aims at investigating whether and how much seismic retrofitting may improve not only the earthquake resistance but also robustness. A four-storey, five-bay, RC frame building designed according to Eurocode 2 is considered as a case study. The frame was assessed by evaluating: 1) the capacity of the structure to redistribute loads after a local damaging event; 2) the seismic capacity of the structure. Non-linear static analyses, i.e., PushDown and PushOver analyses, were carried out in OpenSees to evaluate the robustness and seismic resistance of the structure, respectively. The progressive collapse capacity was evaluated under two relevant column-removal scenarios, i.e., the sudden loss of an internal and an external column, while the seismic resistance was assessed under two load distributions, i.e., proportional to the first vibration mode and to the inertia masses. Subsequently, the impact of retrofitting with carbon fibre-reinforced polymers on both structural robustness and seismic resistance was evaluated. The use of the retrofit measure allowed, on the one hand, the removal of all the shear failures due to horizontal seismic actions and, on the other hand, to increase the robustness of the structure.