PSI - Issue 44

Annalisa Rosti et al. / Procedia Structural Integrity 44 (2023) 91–98 Annalisa Rosti et al. / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction

The 2016-2017 Central Italy seismic sequence confirmed the significant vulnerability of masonry churches to earthquake shaking (e.g. Doglioni et al. 1994; D’Ayala 1999; Lagomarsino and Podestà 2004a; da Porto et al. 2012; Lagomarsino 2012; Sorrentino et al. 2014; Penna et al. 2019). With respect to ordinary buildings, churches are intrinsically more vulnerable due to their architectural configuration, generally characterized by slender walls, wide halls without internal diaphragms, presence of projections (e.g. pinnacles) and thrusting elements (e.g. arches and vaults), which contribute to increase their susceptibility to be damaged by a seismic event. Accurate estimates of the seismic vulnerability of the cultural heritage are essential both for its preservation and for the reduction of potential losses due to future earthquakes. This aspect is of wide concern in Italy, and particularly for churches, given their public, societal and cultural value and given their relevance in the national historical and architectural heritage. Based on these considerations, existing studies assessed the empirical seismic vulnerability of Italian masonry churches by deriving damage probability matrices (e.g. Lagomarsino and Podestà 2004b, c; De Matteis et al. 2016; Canuti et al. 2021; Salzano et al. 2022) or fragility curves (e.g. Lagomarsino and Podestà 2004b; Cescatti et al. 2020; Marotta et al. 2021). Analogously to other empirical studies dealing with existing residential buildings (e.g. Rota et al. 2008; Rosti et al. 2021, 2022), this work investigates the seismic vulnerability of Italian unreinforced masonry churches by statistically processing post-earthquake data collected during the 2016-2017 Central Italy damage and usability assessment campaign (e.g. Sisti et al. 2019). The damage database, gathering 3356 post-earthquake survey form, is first critically examined to identify the dataset of masonry churches to be used in the statistical elaborations. A suitable damage metric is employed for defining global damage levels starting from damage information on individual damage mechanisms, available from the post-earthquake survey form. The peak ground acceleration, estimated from INGV ShakeMaps (Michelini et al. 2020), is selected for punctually characterizing the ground motion severity (e.g. Rosti et al. 2020). Following data processing and homogenization, damage probability matrices (e.g. Rosti et al. 2018) are derived by statistically processing the dataset of 1843 masonry churches, then refined based on census attributes. Observational damage frequencies are also approximated by the binomial model, with the advantage of reproducing the overall damage distribution by a single parameter. 2. The post-earthquake damage database This study exploits post-earthquake damage data collected in the aftermath of the 2016-2017 Central Italy seismic sequence for providing some insights on the empirical vulnerability of Italian URM churches. The adopted post earthquake damage database is the outcome of the intense and synergistic work carried out by the Italian University Laboratories Network of Earthquake Engineering (ReLUIS) and by the Eucentre Foundation, under the supervision of the Italian Department of Civil Protection (DPC). Similarly to the observed damage database of residential buildings, Da.D.O. (Dolce et al. 2019), the 2016-2017 Central Italy database will be integrated in the web-GIS platform Da.D.O.- Churches, together with post-earthquake damage data observed on Italian churches in the last 25 years. The Central Italy damage database, gathering 3356 post-earthquake survey forms, was first critically examined to identify the dataset of masonry churches to be used for statistical analyses. Survey forms missing information on damage and/or usability assessment were removed, together with those related to churches with vertical structure different from masonry or to structures different from churches, such as towers and bell towers. Cleansing of the database and suitable consideration of possible multiple post-earthquake inspections due to repeated earthquake shaking (e.g. Penna et al. 2019) led to the identification of 2009 post-earthquake survey forms associated with 1843 masonry churches (Fig. 1). About 91% of the considered churches were inspected once, whilst damage and usability were reassessed for about 9% of the considered sample, following repeated ground shaking.