DEVELOPMENT OF FRAGILITY CURVES OF MASONRY BUILDINGS BUILD IN A REGULAR ROW AGGREGATE

The 2020 earthquakes in Zagreb caused significant structural damage to historic masonry buildings in the city centre although the earthquakes were of moderate magnitude. Typical brick masonry buildings were built in the late 19th and early 20th centuries with three or more stories in height. These buildings are characterised by load-bearing walls dominantly positioned in longitudinal direction that is parallel to the street and wooden beam horizontal structures with a span of approximately 5 to 6 meters. They also have a relatively high interstorey height of around 3.5 to 4 metres. Moreover, such buildings are usually built within city blocks in the form of regular aggregate. A post-earthquake damage revealed that the position of the building within the block as well as differences in height of adjacent buildings has an important role in its behaviour during the earthquake. The topic of this paper is the seismic assessment of a typical historical building in the centre of Zagreb. Fragility curves are developed for the case of a building within the row aggregate by also modelling two adjacent buildings that have a different height than the buildings in question. Non-linear time history analyses are performed on a 3D model in the Tremuri software - which works according to the equivalent frame approach- with the aim of developing fragility curves associated to the in-plane global response. Out-of-plane wall failure mechanisms are also considered, and the fragility curves are developed for this case by referring to the macro-block model strategy. Special attention is paid to the selection of ground motion records for the site. The on-site hazard is calculated using probabilistic seismic hazard assessment while ground motions for each intensity level are selected based on the conditional spectrum. The comparison of fragility curves associated to two damage modes highlighted a higher vulnerability to the out-of-plane response with is consistent with the evidence from the actual observed damage.