Seismic retrofitting strategies for pre-70 RC buildings: the effectiveness of “local interventions”

Abstract

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, often exhibiting shear failures in beams/columns and beam-column joints. 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 can 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. These buildings have been located in several sites in Italy, characterized by different seismic hazard, and they have been assessed, as commonly performed in design practice, in a code-based approach according to Italian seismic prescriptions, post-processing the occurrence of shear failures. For each building/site, the safety index has been evaluated at two different limit states. Their retrofit has been designed aiming at the resolution of the detected shear failures. Resulting seismic performance are compared to seismic demand in all the considered sites to quantify the effectiveness of the adopted retrofitting strategy depending on the seismic hazard throughout all the Italian country. Lastly, a preliminary estimation of cost of intervention is also presented.