PSI - Issue 78

Shahin Sayyad et al. / Procedia Structural Integrity 78 (2026) 277–284

279

measuring approximately 4.8 m by 3.8 m at the base and tapering to about 3.8 m by 3.3 m from a height of 2.5 m up to the top bell chamber.

Fig. 1. Side view of the bell tower of the San Giuseppe church, along with its ground floor plan.

Due to difficulties in logistics and costs, building materials for the historic building sites usually came from nearby Mount Etna area. For more information on the building material of the Mount Etna area, readers are referred to (Li Rosi et al., 2024). With reference to different local masonry main types, the approximate realistic ranges of their mechanical parameters are summarised in Table 1. The ranges of the values in the table were taken as a starting point to set the first-step input parameters for the FEM of the tower, and were used to verify the admissibility of the values obtained after the calibration. The masonry of the tower of San Giuseppe shows intermediate characteristics between the first two types. The lower part of the tower features higher-quality masonry, with more carefully arranged, larger stones and a more cohesive mortar. The upper part of the tower has lower-quality masonry, and the walls were repaired over the centuries after severe structural damage.

Table 1. Mechanical characteristics of historic masonry in the Mount Etna area.

E sec

fc







E/fc

[kg/m 3 ]

[kN/m 3 ] 15.7-20.6 16.2-21.6 19.6-24.5

[MPa]

[-]

[MPa] 0.3-0.5

1 2 3

1600÷2100 1800÷2200 2000÷2500

500-1600 2300-5200 2400-16000

0.15-0.4 0.15-0.4 0.2-0.4

1670-3200 1000-2260 920-6150

MASONRY TYPE

2.3 2.6

2.2. Operational Modal Analysis The dynamic identification of the building is based on the results of an operational modal analysis conducted using the Frequency Domain Decomposition (FDD) method, which had been previously applied to the structure. In this study, six different Tromino instruments, wireless, three-axial velocimeters designed to measure environmental vibrations with high precision in the 0.1 – 200 Hz frequency range were used. The instruments were mounted at the corners of the internal stair landings and the window sills at three different levels of the tower to capture both torsional and flexural modes through operational modal analysis. The first three identified frequencies are 3.94 Hz, 4.50 Hz, and 9.78 Hz, corresponding respectively to the first bending mode in the East/West direction (B1), the second bending mode in the North/South direction (B2), and the first torsional mode (T1). 2.3. Finite Element Modeling and Eigenvalue Analysis A detailed 3D finite element model of the bell tower using four-node tetrahedral elements with an average element size of 300 mm and a fixed-base boundary condition was developed in Midas FEA NX to account for its geometric peculiarities and intricate modeling features, whereas accurately modeling the 3D geometry of such a structure in OpenSeesPy with fine meshing is very difficult, if not impossible. Based on the results of the previous study (Li Rosi et al., 2024), the southeastern wall shared with the church was considered an integral part of the tower, whereas the rest of the church wall was assumed to have no effective connection and was excluded from the model, resulting in a