PSI - Issue 64

Elide Nastri et al. / Procedia Structural Integrity 64 (2024) 153–160 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The tower's base includes an acute arched opening for a public road, while each level is defined by projecting cornices. The second level features limestone-framed rectangular openings, and the third and fourth levels showcase biforas. At the fifth level, the tower transitions to an octagonal outline, ending in cylindrical turrets. Its façade reflects Arab-Norman art influences, with acute arched openings and biforas framed by relief arches and pilasters. Historical restorations, particularly after seismic events, underscore ongoing preservation efforts for this medieval structure, which also includes the incorporation of iron chains. The photogrammetric survey of the tower involved both drone and terrestrial techniques (Fig. 2a). Drone photogrammetry offered new perspectives and metric information, capturing the complex geometries of the building (DJI professional drone, equipped with a GPS system (GNSS) and camera (CMOS 1/2.3” – 12 MP, 4k/30 FPS video). Terrestrial photogrammetry, using a semi-professional camera (CMOS 22.3x14.9 mm – 24.7 MP), complemented the aerial survey, generating a dense point cloud of the bell tower through Agisoft Photoscan software (Fig. 2b). Geometrically, the tower's transition from square to octagonal geometry is notable, achieved through the addition of cylindrical turrets. The base's acute arched opening and the biforas on higher levels, framed in limestone, are key features. Metal chains are also observed alongside the openings. The roof, made of brick and added post-construction, crowns the structure, while each level varies significantly in height. The presence of bells on the third and fourth levels adds to the tower's functional significance. a b

Fig. 2. (a) Photogrammetry; (b) dense point cloud.

3. Finite Element modelling To conduct a dynamic characterization of the bell tower and evaluate its seismic response to varying intensities, a detailed finite element (FE) model has been created using Abaqus software (ver. 2017). The validation process of the FE model involved meticulous comparison with actual measurements obtained directly from the bell tower itself, ensuring accuracy and reliability in simulating seismic behaviour. This validation included comparing frequency predictions with data from structural health monitoring conducted through ambient vibration tests (AVT) by Chisari et al. (2023).