PSI - Issue 44

Romina Sisti et al. / Procedia Structural Integrity 44 (2023) 1380–1387 Romina Sisti et al. / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction The damage assessment of masonry churches after several recent seismic events has highlighted the high vulnerability of the monumental heritage and the crucial importance of reducing the seismic risk to guarantee their preservation. Such a greater vulnerability compared to ordinary masonry buildings is mainly due to special structural features (wide halls, thin long span vaults, slender walls with large opening, trusting horizontal structures, etc…), often combined with large volumes and the lack of proper strengthening interventions aimed to limit out-of-plane mechanisms (Giresini 2022, Solarino et al. 2021). After the earthquakes occurred in Italy in the last decades (Friuli 1976, Umbria-Marche 1997, Molise 2002, Abruzzo 2009, Emilia 2012, Central Italy 2016-2017), several studies on masonry buildings have highlighted the recurring activation of specific damage mechanisms (D’Ayala and Speranza 2003, Casapulla et al. 2021). Similarly, the observed damage to churches has shown that their seismic behavior can be studied through the subdivision of the structure into macro-elements, i.e. portions architecturally defined (façade, apse, bell tower, dome, nave), which may exhibit an independent structural response with respect to the behavior of the whole church (Doglioni et al. 1994, Lagomarsino and Podestà 2005). The present paper is focused on the assessment of the damage to masonry churches located in Central Italy and inspected after the 2016-17 seismic sequence, in order to define fragility curves based on the empirical/observation approach. Detailed descriptions of the damage to masonry churches after the Central Italy seismic sequence have already been reported by Casapulla et al. (2017), Cescatti et al. (2019), and Penna et al. (2019). The main aim of this paper is a more exhaustive examination of the damage suffered by the churches hit by the Central Italy seismic sequence thanks to a wider set of observational data available and with reference to the estimation of both the global damage and the damage associated with single macro-elements and mechanisms. The latter aspect has, indeed, never been investigated in detail, while it can be very useful to highlight the influence of the damage suffered by specific macro-elements and mechanisms on the global damage level of the church and eventually to point out targeted interventions to reduce the seismic vulnerability of the whole church. During the post-earthquake emergency phases, a large number of churches were inspected to assess their usability, aimed at determining the countermeasures to be taken, and to assess the extent of the damage by estimating a global damage index. The survey phases were managed by the Ministry of Cultural Heritage and Activities (MiBACT), the Department of Italian Civil Protection (DPC) and the Network of the University Laboratories of Seismic Engineering (ReLUIS). The results of the surveys were collected in a predefined form: the A-DC form, officially adopted by the DPC since 2006 (DPCM 2006). At a later stage, the data relating to 3250 inspections were digitalized and collected in a database searchable on the IT-platform Da.D.O. Churches created by DPC and Eucentre (Calderini et al. 2022) (https://egeos.eucentre.it/danno_osservato/web/danno_osservato). The paper presents the empirical fragility curves obtained starting from the damage probability matrices (DPMs) for discrete intervals of PGA (peak ground acceleration) and referred to five damage levels built based on the A-DC forms collected for 3250 masonry churches. The analytical expressions of the fragility curves are determined via the maximum likelihood estimation method and by adopting a lognormal cumulative function to determine the exceedance probabilities of the considered five damage levels. The fragility functions are drawn with reference to both the global damage index of the whole church and the damage index associated to specific macro-elements and mechanisms in order to identify the influence of the latter ones into determining the global damage level. 2. Main characteristic of the church database In 2016-2017 four regions of Central Italy (Abruzzo, Lazio, Marche, Umbria) were affected by a seismic sequence characterized by over 118000 earthquakes (Borzi et al. 2018, Luzi et al. 2017). Starting from the database of 3250 masonry churches collected in the IT-platform Da.D.O. Churches (https://egeos.eucentre.it/danno_osservato/web/danno_osservato), as a first step, the records relating to the following conditions are excluded: churches in a state of ruin before the earthquakes, buildings not identifiable as churches, incomplete assessment of the damage. Furthermore, when several inspections were carried out on the same church due to the repetition of significant aftershocks, only the first inspection is considered in order to exclude cumulative damage. Finally, the analyses illustrated in the following relate to a database of 2884 records.