# An Overview of the Historical Retrofitting Interventions on Churches in Central Italy
###### Abstract
Recent experimental results from the scientific literature reveal, for instance, that GFRP or CFRP reinforcements provide cost-efficient solutions to improve the response of masonry structures under seismic actions [38; 39], as these systems can inhibit both wall overturning and horizontal bending in naive walls, favoring a box behavior. Solutions based on joint reinforcement with steel bars, particularly applicable to masonry with regular courses, have been proposed as well [40]. Regarding roofing interventions, different diaphragm solutions, either rigid [41; 42] or deformable [43], have been investigated in order to mitigate wall overloading. In this case, particular attention has been paid to evaluating the beam-masnory connection to prevent out-of-plane failure modes [44]. Common to all these interventions and improvement strategies is the cost optimization, aimed at justifying the economic investment driving the addressed solutions [45; 46]. As for churches, retrofitting interventions are still a hot topic, as these buildings represent the layered historical identity of the Italian cultural heritage and are subject to many restrictions. As such, it is important to analyze thoroughly their seismic performance in order to carry out targeted interventions, capable of reducing their vulnerability [47] while preserving their cultural, artistic and historical value. To this end, this paper presents an overview of the most widespread anti-seismic interventions conducted in Italian churches and provides a critical analysis of their effectiveness in light of the 2016 Central Italy earthquake. The study stems from an in-depth reconnaissance activity carried out on behalf of the Department of Civil Protection in support of the Italian Ministry of Cultural Heritage, which involved various researchers from several Italian Universities, who shared photos, evaluation reports and other documents, such as the compiled A-DC forms for churches [48]. The data collected were made available to the scientific community through the development of the Da.D.O. (Observed Damage Database) web platform, developed by the Eucentre Foundation for the Italian Civil Protection [49]. In this platform, 4016 churches--surveyed for emergency management purposes after the 2016-2017 seismic sequence--were catalogued in terms of structural/stylistic features, damage and photos. Almost 600 of these churches were subjected to retrofitting interventions in the past, 145 of which were directly surveyed by the authors (Figure 1). The considered sample of 600 churches is spread throughout a large territorial area that has a fair seismic history (the most recent event before 2016 was the Umbria-Marche 1997 earthquake), characterized by earthquakes with different magnitudes and zones that were differently affected. This allowed us to observe several levels of intervention on the original structures and to identify the post-earthquake reconstruction during which they were applied. Several studies have been published in recent times about the effectiveness of antiseismic devices for ordinary masonry buildings during the 2016-2017 seismic sequence. In most cases, the analyses were limited to the municipal level; relevant examples in this regard are the works by [PERSON] et al. [50] and [PERSON] et al. [51], to mention a few, with both having as the object of study the buildings located within the historical hearth of Norcia, the town closest to the epicenter of the October 2016 earthquake. Regarding Central Italy masonry churches, many scientific works have addressed their structural performance under seismic actions, yet no systematic correlation between damage levels and past interventions has been ever drawn. Moreover, the focus has been on specific churches or to a circumscribed number of them [52; 53; 54; 55], hindering statistically significant analyses at the regional and supraregional scales.