Unreinforced masonry buildings, particularly widespread in historic centers of small and medium towns, frequently exhibit a strong vulnerability to seismic actions, often due to their susceptibility to out-of-plane mechanisms (Cima et al., 2021). In order to provide for safeguard interventions, it is fundamental to dispose of approaches able to assess the vulnerability of these buildings on a large scale. In this context, one of the most effective approaches in predicting potential damages of existing buildings, is related to the construction of fragility curves. An important aspect that affects the construction of these curves is the choice of response spectra to define the seismic demand; both Italian code and European guidelines allow the use of natural records, but also propose the employ of smoothed spectra, in that the first one is hardly applicable by practitioners. Nevertheless, the employ of the smoothed spectra could overestimate the seismic demand.

Downstream of this brief discussion, the paper presents the evaluation of fragility curves for the unreinforced masonry buildings of the historical center of Sora (FR), a typical medium town of the Central Italy, regards to the occurrence of out-of-plane collapse mechanisms. In particular, in the work both spectral-shapes proposed by the Italian code and combinations of natural spectra, compatible with the reference spectra of the examined site, have been considered in order to analyze their effects on the fragility curves.