From code to performance: Probabilistic seismic response of retrofitted precast RC buildings

Inadequate detailing in precast buildings designed under previous codes has proven to be a key factor in the seismic vulnerability of Italy's industrial heritage. Advances in structural assessment and refined hazard mapping have led to strategies now embedded in design guidelines; however, their actual probabilistic performance remains an open issue. This paper investigates the probabilistic seismic vulnerability of four single-story precast RC buildings constructed between the 1960s and 1990s, each emblematic of its decade, in a high seismic hazard area designed according to the codes of the time and retrofitted according to the current Italian code. A rigorous validation of standard code-compliant retrofit strategies is proposed, using a fully probabilistic framework that incorporates non-linear pushover analysis, multi-stripe analyses, and fragility derivation methods, which are typically not used in practical code-based design verification. For each case, the effectiveness of the designed retrofit measures is assessed through advanced analyses at two performance levels: usability preventing damage (UPD) and global collapse (GC). Results show that highly invasive global retrofit solutions achieve safety targets consistent with current code requirements for Global Collapse. Furthermore, all proposed interventions substantially reduce the mean annual failure rate for the UPD limit state, keeping retrofitted archetypes within safety margins. Overall, the study provides a concise quantitative benchmark for assessing the effectiveness of current retrofit standards for precast industrial buildings on a probabilistic basis, tailored to specific typologies from different decades.