Downtime-based seismic assessment: insights from new and retrofitted RC buildings in Italy

Post-earthquake resilience goals require seismic design and retrofitting strategies that minimise downtime, beyond ensuring life safety alone. Current seismic codes, including the Italian NTC-18, overlook downtime-related performance metrics, implicitly accepting functional disruption and damage after moderate to severe seismic events. This study examines the seismic performance of both newly designed and retrofitted reinforced concrete (RC) buildings in Italy, in terms of expected annual downtime, recovery time trajectories, and associated economic losses. To do so, four new RC residential buildings, designed according to NTC-18 for a high seismic hazard level, were assessed through a component-based loss assessment methodology using Multiple Stripe Analysis. Then, an existing RC school building from the 1960s–70s was also analysed under a high seismic hazard scenario, adopting the same loss assessment approach. For the existing building, four distinct retrofit strategies were selected and compared in terms of median downtime (in days) to achieve re-occupancy and functional recovery states, for different return periods. For both new and existing buildings, a recently proposed post-earthquake recovery assessment methodology was employed to assess recovery time trajectories, accounting for different impeding factors. Overall, the findings highlight the need to foresee downtime-based limit states in seismic codes, supporting the European objectives for sustainable and resilient built environments.