Existing RC buildings are often vulnerable to seismic loading, thus requiring retrofitting strategies to mitigate such vulnerability. This is certainly true for existing RC buildings realized in Italy before ‘70s and often designed to sustain gravity loads only. Such (low-standard) RC buildings typically present failure typologies very different from newly designed buildings, and such failure modes should be properly modelled for a reliable seismic performance assessment. Retrofitting strategies should be chosen carefully looking at safety at collapse, but also at seismic capacity at less severe performance levels, considering non-structural components as well, which significantly affect expected annual losses.

In this work, the as-built assessment and the retrofit design and assessment of Italian pre-70 RC case-study buildings – designed for gravity loads only - is presented. Case-study buildings have been first assessed without considering infills, as common in design practice, in a code-based approach according to Italian seismic prescriptions, post-processing the occurrence of shear failures. Their retrofit has been designed aiming at (i) the resolution of the (detected or potential) shear failures and (ii) the increase in displacement capacity in RC members involved in the collapse mechanism. Then, both the as-built and retrofitted building configurations have been modelled and analyzed explicitly considering the presence of infills and shear-critical elements. Resulting seismic performance are obtained and compared to each other to quantify the effectiveness of the adopted retrofitted strategies, considering different seismic intensities. A preliminary estimation of the expected mean annual losses for the investigated buildings is also presented, to find out how much such interventions on existing buildings could be effective in reducing seismic losses, without the stiffening of the building or eventual interventions on masonry infills.