Post-earthquake dynamic monitoring of a historic masonry tower

The Gabbia Tower, about 54.0 m high and dating back to the XIII century, is the tallest tower in Mantua, overlooking the historic centre listed within the UNESCO Heritage. After the seismic sequence of May 2012, an extensive research program was carried out to assess the structural condition of the tower. The post-earthquake investigation (including direct survey, historic and documentary research, testing of materials and ambient vibration tests) highlighted the poor state of preservation of the upper part of the building and suggested the installation of a dynamic monitoring system to evaluate the response of the tower to the expected sequence of far-field earthquakes and check the possible evolution of the structural behaviour. After a brief description of the tower and the post-earthquake survey, the paper presents the results of the continuous dynamic monitoring for a period of 8 months, highlighting the effect of temperature on automatically identified natural frequencies, the practical feasibility of damage detection methods based on natural frequencies shifts and the key role of permanent dynamic monitoring in the diagnosis of the investigated historic building.