Nowadays, there is still very little scientific understanding of the seismic response of mixed masonry-r.c. structures, despite their unneglectable frequency, in particular in public building assets.

This contribution presents the investigations carried out on a representative school, built at the turn of 1950s and 1960s. It has two storeys, and its structural system is characterised by central longitudinal load-bearing masonry walls, as well as a number of transverse masonry panels, coupled with r.c. frames on major façades, and isolated columns in halls. This structural configuration is commonly found in public buildings, specifically schools, built before the emergence of r.c. technology. R.c. elements were exploited to build open-space environments, as well as to increase openings on façades, thus ensuring a better natural lighting.

In this study, masonry components were modelled through an equivalent frame model (EFM), and r.c. frames were represented through finite elements (i.e., beams). In addition, half-height infills, interacting with frames, were simulated through a single-strut macro-model. To simulate the nonlinear response of the structure, lumped plasticity hinges were implemented for both load-bearing masonry and infills, while a fibre model was chosen for r.c. frames. The presence of non-seismic joints among structural units was also considered.

The relative contribution of masonry and r.c. components was investigated through parametric linear dynamic analyses. Then, nonlinear static analyses (NLSA) were carried out to investigate the evolution of damage for an increasing seismic action. Moreover, the structure was analysed through nonlinear time history analyses (NLTHA) by applying a large number of unscaled ground motion records.

Lastly, fragility curves were estimated from outcomes of NLTHA for four damage states (DS), from slight damage to incipient collapse. The maximum interstorey drift ratio (IDR) was set as demand parameter, for which threshold values, to identify DS, were estimated by processing results of NLSA.

The derived fragility model represents a key instrument in seismic risk evaluations for homogeneous structures, being one of the few examples of fragility sets specific for mixed masonry-r.c. buildings.