# An Overview of the Historical Retrofitting Interventions on Churches in Central Italy
## 3 The Main Interventions Observed in Central Italy
### Wooden Elements  
One of the most consolidated \"rules of thumb\" to improve the seismic response of masonry churches under earthquakes was the insertion of wooden elements into walls and vaulted systems. Different technical procedures were used to embed these strengthening devices within the masonry. The aim was to exploit the tensile strength of the timber so as to compensate for the poor tensile resistance of the masonry and to reduce sliding between rubble stones. Also known as \"ties\" or \"roots\", wooden elements were usually placed within the entire thickness of the wall running from one face to another, in order to bind together multiple leaves and improve the wall stability by preventing crack propagation (Figure 10a). Another way to apply these roots was to arrange them continuously within the perimeter of the building, at the floor level, holding the walls together and fostering a box-like behavior (Figure 10b). This latter timber-laced solution was a very common practice [69] in the seismic areas of Central Italy. An example found in the church of [PERSON], damaged by the 2009 Aquila earthquake, can be observed in Figure 11. It is worth noting that, besides exerting a reinforcement function, embedded wooden elements also helped prevent structural failures during the construction process of masonry churches, especially in the presence of vaults [74], domes and bell towers. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Year** & **Epicentral Area** & **Mw** & **Year** & **Epicentral Area** & **Mw** & **Year** & **Epicentral Area** & **Mw** \\ \hline
1767 & Valle Umbra & 5.5 & 1898 & Valnerina & 5.0 & 1997 &
\begin{tabular}{c} Appennino \\ umbro-marchigiano \\ \end{tabular} & 5.5 \\
1771 & Sorano & 5.1 & 1898 & Valnerina & 5.5 & 1997 & Valnerina & 5.2 \\
1785 & Appennino & 5.1 & 1899 & Colli Albani & 5.1 & 1997 & Valnerina & 5.6 \\
1785 & Momti Reatini & 5.8 & 1901 & Sabina & 5.3 & 1998 &
\begin{tabular}{c} Appennino \\ umbro-marchigiano \\ \end{tabular} & 5.0 \\
1791 & L’Aquila & 5.3 & 1901 & Sorano & 5.2 & 1998 &
\begin{tabular}{c} Appennino \\ umbro-marchigiano \\ \end{tabular} & 5.3 \\
1791 & Appennino & 5.6 & 1904 & Marsica & 5.7 & 1998 &
\begin{tabular}{c} Appennino \\ umbro-marchigiano \\ \end{tabular} & 5.1 \\
1792 & Temano & 5.1 & 1905 & Valle Peligna & 5.2 & & \\
1793 & Appennino & 5.3 & 1915 & Marsica & 7.1 & & \\
1799 & Appennino & 6.2 & 1915 & Marsica & 5.0 & & \\
1799 & Foligno & 5.1 & 1915 & Marsica & 5.1 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cont. As far as vaulted systems are concerned, the insertion of wooden beams had the specific purpose of absorbing the horizontal thrust. Occasionally, not to be visible from the inside, these elements were positioned at the vault extrados, but their effectiveness in restraining thrust-induced outward movements at the springing level was limited (Figure 12a). Indeed, extrados tie-rods provide an efficient restraining action only in the presence of high compression loads, as vertical actions counteract the pier rotation (Figure 12b). The placing of ties in line with possible hinge locations was used in the past: in fact, specific tying devices called \"tie slings\" (_tiranti a braga_) were often used to transfer the effect of the tie-rods to the arch impost and to prevent the rotation of the piers. To make these anti-seismic devices further effective, they were flanked by two additional wooden beams counteracting the deformations of the vault (Figure 12c). This solution was adopted for instance in the vaults of the central wave of the church of San Domenico in L'Aquila (Figure 13a). It is noted that, to prevent the horizontal tie rod from deforming owing to the presence of oblique elements, the device must be suitably rigid. Still, this was not always the case in historic structures. A different solution, which became the most popular, was the insertion of wooden beams at the level of the arch impost.