# Acoustic Emission for Structural Monitoring of Historical Masonry: An In-Field Application
## 4 Case Study: Santa Maria Delle Grazie  
The Santa Maria delle Grazie complex is a masonry structure situated in the municipality of Barano in the southeastern part of Ischia Island. Figure 1: (a) Kaiser effect; (b) Felicity ratio [27]. The building was selected as the test site based on several key considerations. The structure forms part of a culturally and historically valuable heritage site, subject to strict conservation regulations, making non-invasive diagnostic techniques essential. This condition offered a suitable scenario for testing AE techniques under semi-controlled loading conditions on a rehabilitated structural element. The presence of a reinforced but still heterogeneous masonry arch allowed for the investigation of internal damage phenomena and stress redistribution mechanisms without compromising the structural safety or historical value of the building. Due to its relevance, the site also hosted an experimental campaign involving the use of optical fibre-based sensing systems [31; 32; 33]. The structure is made of several elements. The church and the related annexed buildings were built for religious purposes at the behest of the [PERSON] family in the late Baroque period, who lived in the annexe behind the church. In 1883, the structures were damaged by the earthquake of Casamicicola Terme. No restoration work is documented, at least until 1889. However, it is probable that some minimal interventions were carried out in the following years, just as it is impossible to attribute to that seismic event the instability that still interests researchers in the artefact today. It was certainly open to worship until the first few decades of the twentieth century. Upon the death of [PERSON] in 1920, the church was closed. In the first few decades of the last century, [PERSON]'s family left Barano, moving to another municipality of the Isle. Since then, the continuous hereditary disputes that developed within the family led to the progressive abandonment of the complex. The lack of maintenance over several decades is undoubtedly the leading cause of the substantial deterioration. In 1992, the last heirs, [PERSON] and [PERSON], sold the entire complex, including the Chapel, to the Municipality of Barano. The structure is made of Arso lava stone and lime mortar, with some parts arranged in regular blocks and others chaotically. The horizontals were made up of stone barrels, cross vaults, and wooden floors. Nowadays, the monument is subjected to restoration work since the state of the structure was very poor (Figure 2), and the whole complex was almost entirely obstructed by weeds, which had grown freely over the years of neglect. The deterioration has also been increased by the continuous exposure of the building to atmospheric agents due to its apical and isolated position. The church, occupying the ground floor, was entirely devoid of a roof, affected by a generalised collapse. The edge wall structures were intact and protected by a finishing layer of painted plaster enriched with various mouldings. The church's facade almost entirely lacks plaster. The annexes behind the church were residential areas, with some walls remaining and others having collapsed or been demolished for safety purposes. The first basement floor is about three metres beneath road level. The related facade bordering the road has no windows, while the other three sides open freely onto the surrounding landscape. This floor mainly had service areas, such as rooms, vats for vinification, kitchens, and washrooms. The east and south sides opened onto panoramic balconies and loggias as part of arcades, probably added at a later date. In some cases, arches effectively disconnected the facades. The structural consolidation works aim to improve static and seismic capacity through a series of global and local interventions [34; 35; 36].