ANIDIS - L'ingegneria Sismica in Italia, ANIDIS XIX & ASSISi XVII - 2022

Dimensione del carattere:  Piccola  Media  Grande

Dynamic identification of the tabernacle of the church of Santa Maria Maggiore in Spello, Italy

Matteo Castellani, Nicola Cavalagli, Enrique Garcia-Macias, Filippo Ubertini, Riccardo Vetturini

Ultima modifica: 2022-08-30


The conservation of architectural heritage is a primary concern for the preservation of the cultural identity of a population and of the tangible proofs of historic architectural development. In most of the cases, architectural artifacts must be protected over time from all the threats that could derive by both the variation of inherent properties, as the aging of the constituent materials, and external actions, such as natural hazards and strong events, typically earthquakes. The preservation of architectural heritage against seismic events requires an in-depth knowledge of its dynamic properties, which can be affected also by local damages and material degradation.

In this work, the experimental tests carried out on the tabernacle of the church of Santa Maria Maggiore in Spello (Italy) for the estimation of its dynamic properties are presented. The tabernacle, made of caciolfa stone, has been built at the beginning of the 16th Century and is characterized by four columns of about 3 meters high, supporting four stone arches on which a hemispheric dome rises, reaching a total height of about 8 meters. In plan the structure has a square regular shape, with each side of about 4 meters length. The architectural artifact has been built by connecting stone elements through internal iron bars, resulting in a multi-block structure with a complex dynamic behavior.

An important role for the historical conservation of cultural heritage is entrusted to three-dimensional reconstruction of the built through the innovated techniques of Laser Scanner combined with UAV photogrammetry in extremely confined settings. The synergy between these two different methods allows to assess with high degree of confidence the geometry of the built, essential in the reconstruction process of a digital model at the foundation of the successive analysis

For the dynamic identification campaign we have used Ambient Vibration Tests (AVTs) carried out through high-sensitivity uni-axial accelerometers placed at the base of the columns, at the base of the arch and at the base of the dome. Through a National Instrument acquisition system, data were recorded through the use of 24 channels divided in three different setups with a sample rate of about 1650 Hz. The dynamic identification procedures, developed in frequency and time domains, have allowed to estimate the first natural frequencies and the related mode shapes of the structures, highlighting the complex behavior of such systems, which modes are characterized by polyline shapes with tangent discontinuities placed in correspondence to the joints of the stone elements.

In order to verify any effects of non-linearty and motion in free oscillation, the tabernacle has been instrumented through 8 displacement transducers (LVDT) and subjected to increasing force applied at the height of the shutters of the arches, highlighting a rocking motion due to the presence of hinges located at the base of the column.

The results, also strengthened by the outcomes derived by different nondestructive tests carried out about 20 years ago on the constituent materials, which emphasized the degradation state of the stone material corresponding to the most stressed areas of the joints, have highlighted the crucial role of diagnosis with a multidisciplinary approach in order to achieve proper decisions of interventions in the respect of the cultural heritage.

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