Empirical Performance Levels of Strengthened Masonry Buildings Struck by the 2016 Central Italy Earthquake: Proposal of a New Taxonomy

The complexity of the historical built environment may be reduced by discretizing buildings in types. At urban scale, typological classifications feed vulnerability models. Several literature procedures define types by the evaluation of constructive, geometrical, and structural features, but none seems to consider improving or upgrading interventions. These are the expected performance levels prescribed by seismic codes for strengthening existing masonry buildings. Notwithstanding, the 2016 Central Italy earthquake revealed the potentially detrimental role of interventions on the seismic behaviour of a building. A new performance-based taxonomy of masonry buildings is here proposed starting from the analysis of 2306 inspected dwellings struck by that event. Building features, i.e., masonry and diaphragm types, were matched to strengthening techniques, thus obtaining a preliminary description of that sample. The empirical evidence showed the performance levels of buildings with interventions, which were graded in four categories: upgrading and improvement, downgrading and worsening depending on their compliance with the box-like behaviour. Therefore, an expansion of the coded possible performance levels was found. Those levels entered the final taxonomy of the sample, yielding 15 robust performance-based types, which were cross-validated through the analysis of their most common damage mechanisms.