PSI - Issue 44

S. Monchetti et al. / Procedia Structural Integrity 44 (2023) 1988–1995

1993

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Silvia Monchetti et al. / Structural Integrity Procedia 00 (2022) 000–000

As far as the geometrical characterization of the pulpit is concerned, the first laser scanner survey dates back to 2007 and it was carried out by the Department of Architecture of the University of Ferrara, as reported in Aldrovandi et al. (2011). This experimental activity also included the survey of the Sant’Andrea church of which 2D outputs can be accessed. More recently, the Department of Civil and Environmental Engineering of University of Florence has realized a new geometrical survey using terrestrial laser scanning (TLS) techniques. As reported in Conti et al. (2022), TLS technology enables an optimal acquisition of opaque surfaces with lambertian reflectance (such as those of many materials used in cultural heritage and buildings). However, the acquisition of translucent surfaces or material with a specular reflectance or a high refractive index using TLS techniques is still a challenge. The extremely complex morphology of the pulpit, made of white and red marble, make the geometry acquisition particularly difficult: each element was inevitably acquired at variable distances and angles of incidence. From the overall point model, a surface model was also obtained. This mesh, initially consisting of about 32 million triangles, has been reduced to about 2 million faces for structural evaluation models, balancing the conflicting requirements of high resolution and usability. This computational model, reported in Fig. 3, is used as reference for the developments of the present research from the HBIM definition to the structural analyses, including the identification of the model by using the data from monitoring system. The SHM was placed on the pulpit at the beginning of 2022 as part of research agreement between the Department of Civil and Environmental Engineering (DICEA), the Department of Earth Sciences (DST) from the University of Florence, the “Soprintendenza Archeologia, Belle Arti e Paesaggio per la città metropolitana di Firenze e le province di Pistoia e Prato” (SABAP-FI) and the Association Friends of Florence (FoF) which financed the project. The SHM system aims to control the static and dynamic behaviour of the pulpit under environmental vibrations and in presence of external forcing. The system (see Fig. 4) consists of 6 linear potentiometers, 6 uniaxial accelerometers, 1 electric piezometer, and 1 temperature and relative humidity sensor. The static monitoring involves the acquisition of data every hour, whereas, dynamic monitoring involves one acquisition every 24 hours and when the triggers are activated. This system will acquire data for at least 2 years.

Fig. 4: Layout of the SHM system.

From the data acquired so far, structural eigenfrequencies can be extracted under ambient vibrations. In particular Fig. 5 reports the identification of the first three natural frequencies and mode shapes which will be used for the calibration of the numerical model (Bartoli et al. (2020); Zini et al. (2022)).