Effect of traditional strengthening interventions on seismic fragility of URM buildings

The high level of seismic vulnerability of historical unreinforced masonry (URM) buildings is well known and has been recurrently highlighted by strong earthquakes. Nonetheless, a major knowledge gap on the seismic performance and vulnerability of retrofitted URM buildings. In this study, the vulnerability of URM buildings strengthened with traditional techniques is investigated through structural modelling and probabilistic simulation. The study started with the collection of data on existing masonry buildings, which allowed the exposure modelling in terms of age of construction, type of masonry, type of floor systems, and number of storeys. Data sets were created for one thousand URM buildings that were actually strengthened in the past. Based on a MATLAB code, the structures of the selected buildings were simulated according to an equivalent frame modelling approach, implementing traditional strengthening interventions on the structural components that negatively influenced the seismic performance of as-built URM buildings. Fragility analysis was carried out using nonlinear static analysis, deriving fragility curves for the damage states defined in the European Macroseismic Scale (EMS-98). Then, fragility curves related to retrofitted URM buildings are compared to those derived for their as-built counterparts, quantifying the benefits of traditional strengthening techniques.