OMA and Dynamic SHM of the Urbino Cathedral After the 2016 Central Italy Seismic Events

Following the seismic events that occurred in central Italy on 24–26 August 2016 and 30 October 2016 the Cathedral Basilica of S. Maria Assunta in Urbino reported moderate damage to the main load-bearing structures. Many of this damage had already manifested itself during the seismic events of September 1997. The main critical issues encountered after the quakes concern widespread cracking in the vault barrel of the central nave for hammering of the facade, in the triumphal arches, in the entablature of the drum, in the lantern, in the entablatures of the transepts. The crack pattern corresponds to the onset of typical collapse mechanisms of churches, namely: tilting of the facade due to mechanisms at the top and in the plane of the façade, cracking of the main façade, transversal response of the nave, cracking of the triumphal arches and cracking of the drum, vault and lantern. A restoration project has been defined and implemented (2018–2020), and the cathedral was eventually re-opened to public at the end of 2020. In the framework of the seismic improvement and restoration works, investigation activities including Operational Modal Analysis were carried out, as well as the installation of a SHM system, provided with seismic accelerometers. It was then possible to obtain a pre/post-works dynamic features extraction of the cathedral, as well as having record of all the relevant earthquakes occurred in central Italy (not only, also the Croatian 2020 earthquake was recorded) in the period of presence of the SHM system – still acquiring data.