PSI - Issue 78

Emanuele Rizzi et al. / Procedia Structural Integrity 78 (2026) 1420–1427

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most powerful was the 1908 event that devastated Messina and Reggio Calabria (INGV, 2025). The data from the Catholic Church's cultural heritage web portal (BeWeB, 2025) lists 56259 places of worship, including churches, sanctuaries, and basilicas. Most of these architectural assets were built before seismic risk was fully understood. As a result, these massive monumental structures, often characterized by large spans and heights, are particularly vulnerable to seismic events and are of key concern in earthquake prevention. Most were built using unreinforced brick or stone masonry and have undergone significant structural modifications over time, often leading to increased seismic vulnerability. In some cases, effective measures were implemented, primarily involving the use of iron ties to stabilize arches and vaults and to connect perpendicular walls. Traditionally, three-aisled masonry churches are characterized by nave arcades used to separate the central nave from the side aisles (Fig. 1). They are composed of arches placed at the top of columns or slender piers. Sometimes, the arches present single lancet windows with semicircular arches to illuminate the church nave. Typically, the ceilings of the naves consist of groin vaults or exposed pitched roofs supported by wooden trusses. Many post-earthquake surveys show that the columns supporting the arcades underwent heavy damage and sometimes collapse. For example, during the Friuli earthquake of 1976, the dome of Gemona del Friuli (UD) sustained significant damage. The columns rotated at their bases, leading to noticeable out-of-plane tilting. Structural failure was also observed in the left aisle, primarily due to insufficient bracing (Zanetti et al., 1987). Also the Church of St. Gemma in Goriano Sicoli (AQ) was heavily affected by the L’Aquila earthquake of 2009, suffering severe diagonal cracks in the aisle vaults and crushing of the columns (Criber et al., 2015).

(a)

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Fig. 1. Some examples of historic masonry churches with arcades separating the aisles: (a) Cathedral of St. Stephen the Protomartyr in Concordia Sagittaria (VE); (b) Catholic Parish Church of Our Lady of the Sea in Trieste (TS).

Nave arcades can fail both in-plane (IP) and out-of-plane (OOP) due to horizontal forces, even though the kinematic analysis shows that OOP failures typically occur at much lower spectral accelerations. The in-plane stiffening of the roofs of the central and lateral naves by means of a bracing system effectively connected to the walls, generally represents an intervention that can improve also the IP and OOP seismic performance of these structural elements. The paper focuses on a minimally invasive strengthening intervention, based on the bracing of the roof by means of steel ties. This approach preserves the original aesthetic of the monuments and is fully reversible. A case study of a three-aisled church is considered and the seismic performance of the nave arcade before and after the intervention is analyzed and compared. Structural performance is evaluated through numerical modeling using non-linear static analyses. 2. Case study The geometric characteristics of the case study (Fig. 2a) closely correspond to those of the Cathedral of St. Stephen the Protomartyr in Concordia Sagittaria (VE, Italy). The main hall is divided into three aisles by two rows of slightly pointed arches, built using four-header bond plastered masonry. The dimension of arches is represented in Fig. 2b. All the walls, arches, and columns were built using traditional solid clay brick masonry. The five arches rest on six columns, with the two outer ones built against the perimeter walls. Each column is 5450 mm tall, with a composite cross-section formed by the intersection of a square with 780 mm sides and four semicircles with a radius of 250 mm (Fig. 2c). The spacing between the columns is 6100 mm. The wall thickness is 500 mm. The main façade features two