Towards IoT monitoring of street-side monuments: The Florentine Dietrofront as a case study

The need for care often shown by ageing cultural heritage and the circumstantial lack of dedicated budget are increasingly calling for smart monitoring solutions to shift the maintenance paradigm from reactive-preventive to predictive. Monitoring artworks poses additional issues with respect to the more common industrial solutions, such as aesthetics, dealing with unusual materials, remote locations (archaeology), etc. In this scope, the "Dietrofront" statue in Florence, by artist Michelangelo Pistoletto, is an emblematic instance. Installed on a traffic roundabout, it comprises four travertine blocks, one of which hangs 5 m above the ground supported by a steel structure which has shown relevant symptoms of damage during the 2006 restoration works. During a later intervention, we seized the opportunity to equip the structure with a three IoT sensing devices, so as to monitor thermo-hygrometric conditions, inclination and vibrations of the structure. Various issues common to outdoor monuments have been faced, such as the need for visual non-intrusiveness and the unavailability of power supply. A small wireless sensor network was designed and installed, also exploiting an existing room inside the nearby mediaeval city gate. The network is fully solar-powered by photo-voltaic modules integrated on both the statue and the gate and not visible from the street. The data obtained have been analysed and compared to a simple lumped-parameters structural model, so as to estimate the relevance of traffic-induced vibration on the steel structure. The risk of water vapour condensation has also been assessed.