Improvement of seismic safety by local strenghtning in italian pre-70 residential RC buildings designed for gravity loads

Pre-code reinforced concrete (RC) buildings in Italy are significantly vulnerable to seismic actions, especially those realized before '70s, since, up to'70, about 85% of the whole national territory was classified as not-seismic prone area. In such areas, buildings were designed to sustain gravity loads only, without capacity design principles, often resulting vulnerable to shear failures both in beams/columns and in beam-column joints under seismic loading. Thus, proper retrofit strategies should be analysed and implemented in order to solve such brittle failures, aiming at improving seismic performance at life safety limit state. In this work, the seismic assessment of case-study Italian pre-70s RC buildings and the relevant retrofit design are carried out according to the current Italian technical code (D.M.2018). Two case-study residential buildings, designed for gravity loads only and different for number of stories, are analysed to assess their “as-built” capacity. The latter is compared with the seismic demand at the life safety limit state, considering all Italian municipalities classified as not-seismic area up to'70 as possible building locations. Thus, for each building/site, the capacity-to-demand ratio, is evaluated. Then, local strengthening interventions (wrapping with Fiber Reinforced Polymers strips for beams/columns and CAM® technology for joints) are designed aiming at the complete resolution of the detected shear failures. The post-strengthening seismic capacity is compared to seismic demand to finally quantify the effectiveness of such a local intervention depending on the building height and the current seismic hazard throughout the Italian country.