# An Overview of the Historical Retrofitting Interventions on Churches in Central Italy
## 4 Assessment of the Seismic Interventions
### Effective vs. Ineffective Interventions
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Ring Beam**} & \multicolumn{3}{c}{**Longitudinal Tie**} & \multicolumn{3}{c}{**Trasversal Tie**} \\ \hline  & **\textgreater{}50 km** & **25–50 km** & **\textless{}25 km** & **\textgreater{}50 km** & **25–50 km** & **\textless{}25 km** & **\textgreater{}50 km** & **25–50 km** & **\textless{}25 km** \\ \hline Unusable & 36\% & 50\% & 89\% & 0\% & 17\% & 25\% & 16\% & 25\% & 64\% \\ Partially unusable & 9\% & 6\% & 5\% & 40\% & 17\% & 15\% & 20\% & 13\% & 0\% \\ Accessible with & 27\% & 13\% & 5\% & 20\% & 17\% & 17\% & 24\% & 29\% & 0\% \\ provision & 0\% & 0\% & 0\% & 0\% & 0\% & 5\% & 0\% & 0\% & 7\% \\ Accessible & 27\% & 31\% & 0\% & 40\% &To further investigate the influence of seismic retrofitting measures on the analyzed sample of churches, a valuable comparison was made, taking into account three specific collapse mechanisms strongly influenced by the presence of tie-rods or ring beams: mechanism 1--overturning of the facade, mechanism 2--overturning of the top of the facade, mechanism 5--transversal response of the naive. For each mechanism, the damage level recorded in the churches retrofitted with ties (either deployed transversally or longitudi  
Figure 26: San Martino Church in Amatrice: (**a**,**b**) adverse effect of the RC ring-beam. Figure 25: San Giorgio church in Amatrice: (**a**) external view; (**b**) detail of the “in folio” vault and transversal tie rods. nally) was weighed against the damage level suffered by churches reinforced with rigid RC beams. The first correlation aimed at analyzing the damage caused by the activation of the facade overturning mechanism in churches retrofitted with longitudinal tie-rods versus those retrofitted with RC ring beams. As observed in Figure 27a, only 5% of the churches with tie-rods developed severe damage levels (d3-d4-d5) for the considered collapse mechanism. This percentage increased in presence of rigid RC ring-beams only, increasing to 15% for a damage level of 5, i.e., collapse. Figure 27: Comparison between damage on mechanism 1 (**a**) and mechanism 2 (**b**) in the presence of longitudinal tie rods and RC ring beams; (**c**) comparison between damage on mechanism 5 in the presence of transversal tie rods and RC ring beams. The second comparison was made by examining, for the same churches, a different collapse mechanism, namely the overturning of the top of the facade (Figure 27b). Although the damage trend is similar to mechanism 1, an evident increase in the number of churches suffering from higher damage levels is recorded in the presence of RC ring-beams. According to the results, this collapse mechanism is likely due to the lack of connections between elements and the multi-layer masonry with an inner core made of poor quality rounded stones and with an external masonry made of regular stones (Figure 26). As a final comparison, the damage level resulting from the activation of the mechanism involving the transverse response of the naive was analyzed. In this case, the severity of damage drops in the presence of transversal tie-rods, whereas a higher percentage of churches showing higher levels of damage is found in the presence of RC ring-beams (Figure 27c). Interventions of this type are not a priori incorrect, but for the investigated churches, i.e., masonry structures with Ministry-imposed limitations and macro-element behavior, they were not effective. The results show indeed that the use of stiff roofs, especially if not effectively connected to the underlying load-bearing masonry walls, does not improve the seismic response of the structure; on the contrary, it may lead to unexpected and dangerous seismic behaviors. Lighter steel horizontal diaphragms, properly connected to the vertical resisting system, as well as restraining tie rods between orthogonal walls can provide valid alternatives to reinforced concrete elements in order to foster a better seismic performance. In this regard, interventions against masonry crumbling are also fundamental.