Vulnerability assessment of historical building aggregates in Zagreb: implementation of a macroseismic approach

The European building stock consists of a large number of unreinforced masonry structures. Masonry structures proved themselves to be fragile if subjected to horizontal loads, particularly out-of-plane. The complexity of existing structures during an earthquake increases if they are arranged in aggregates. This research deals with the definition of vulnerability and fragility curves for Croatian existing masonry buildings in aggregates. The curves were derived following the European macroseismic scale (EMS–98). The adopted case study includes three aggregates located in Lower Town in Zagreb, Croatia. The capital of Croatia was hit by a series of earthquakes in March 2020. Until these recent earthquakes, the damage database from previous earthquakes was non-existent. The structural vulnerability was mainly assessed by analytical methods, which were not a proper solution for identifying the seismic risk on a larger scale, ultimately at the state level. The database from this earthquake series enabled the application, validation and calibration of empirical methods. The macroseismic index-based method was applied and based on the observed damage, new formulations to assess the vulnerability are proposed.