Assessment of the acceleration floor spectra through dynamic identification: the Museum of Bargello in Florence

Artworks represent a priceless asset to the economic and cultural features of communities. Most art collections are hosted in Museums, which can be new buildings, appositely made for an expositive purpose, or monumental buildings, whose high artistic and historical value enhances the exposed art pieces. In this latter case, however, the Museums can disregard the seismic safety requirements provided for new constructions, becoming the main source of hazard for the precious contents they should preserve. In this paper, the dynamic behavior of the National Museum of Bargello in Florence is studied by means of a dynamic identification, focusing the attention on the "Sala di Donatello". An experimental campaign was performed by simultaneously installing two sets of three seismometric stations in the mentioned room and inside the corresponding one at the base of the building ("Sala Michelangelo"). Analysis of the recorded data via Operational Modal Analysis techniques has furnished the structure's natural frequencies, damping ratio and mode shapes allowing the assessment of the amplification of the seismic acceleration experienced by the art works exposed in "Sala di Donatello". The effect of the seismic acceleration on the artifacts has been checked on a case-study, i.e. the masterpiece "Marzocco". It is the statue of the lion considered the symbol of Florence, realized by Donatello in 1420, placed on a marble pedestal made by Benedetto da Maiano in 1480, which is a work of art as well. The assessment has been made by performing a simplified rigid-block analysis. The geometrical data of Marzocco has been stated based on a detailed photogrammetric survey, which provided a reliable representation of the mass distribution.