# An Overview of the Historical Retrofitting Interventions on Churches in Central Italy
## 4 Assessment of the Seismic Interventions
### Effective vs. Ineffective Interventions  
In order to proceed with the evaluation process, churches were grouped by structural characteristics and epicentral distances. The first group of churches is located at distance d \(<\) 25 km from the two major epicenters of 24 August and 30 October, which are considered the most influential in terms of magnitude (6.0 Mw and 6.5 Mw, respectively); the second group includes churches located at distance 25 km \(<\) d \(<\) 50 km, while the third group includes churches sited at distance d \(>\) 50 km (Figure 23). Comparing the results in terms of unusability, the data show that, independently of the epicentral distance, churches with ring beams always feature higher percentages of unusability (hence greater severity of seismic damage) than churches with longitudinal  
Figure 23: ShakeMaps for (**a**) 24 August 2016 and (**b**) 30 October 2016 earthquakes in Pga (g). and/or transversal tie rods (Figure 24). For completeness, Table 2 shows the usability percentages obtained for each group of churches. To better understand the impact of the different interventions on the unusability of the buildings, the post-earthquake conditions of two churches (San Giorgio and San Martino), similar in size and distance from the epicenters (10 km distant from the August epicenter and 25 km from the October one), were compared. Both churches are located in Amatrice, one of the Italian towns greatly affected by the 2016 earthquake [93]. Built in the 19 th century, San Giorgio church is a single-nave structure made of plastered irregular masonry, with a gabled facade and vaulted ceiling. To reduce the overall thickness of the vaults and lighten the weight on the underlying walls, bricks were laid flatwise (_\"in folio\"_ vaults). The main intervention carried out in this church over the past years involved the addition of metallic tie-rods at approximately one-third the distance from the impost of the arch in order to retain possible outward movements of the lateral walls. Despite the significant seismic damage occurring in the vaults, with typical diagonal cracks [94] passing through pendentive, the structure remained intact (Figure 25a,b). By contrast, the church of San Martino, a single-nave stonemasonry structure with roof trusses built in the 15 th century, was not able to withstand the seismic sequence of 2016 without being severely damaged. An important intervention was carried out around 1980, with the insertion of RC ring-beams along the perimeter of the church, at the roof level. The inadequate connections with the underlying unreinforced masonry walls, together with the increase in mass originated by the addition of these elements, led to severe collapses. The close-up of Figure 26 clearly shows the lack of anchoring between the ring-beam and the masonry wall below, which favored sliding. It is also important to stress the poor quality of the masonry on which the intervention was made as well as the inappropriate design of the rigid beam, whose width does not equal the wall thickness, thus being ineffective.