Evolution of Modal Parameters of a Reinforced Concrete Building Subjected to Moderate Earthquakes

Results of the dynamic monitoring carried out on a school building located in central Italy during the seismic sequence following the main shock of 2016 Central Italy earthquake are presented in this work. The building, located in the historical centre of Camerino (Marche Region), consists of a reinforced concrete frame structure with masonry infill walls. The school was built in the 1960s and was seismically retrofitted in 2013 through the construction of two dissipative towers, according to a recent patented system for the seismic protection of constructions. The system consists on steel truss towers built outside the building, pinned at their base and connected to the building through braces at the floor levels. Towers are equipped with dissipative devices that activate for the rocking of the tower triggered by the building displacements. In August 2016 a dynamic monitoring system was installed on the building, positioning accelerometers both at the last two floors of the structure and at the foundation level. The system allowed the recording of the building response to the aftershocks occurred during the monitoring period, and of the corresponding seismic input. Registrations are used to track of the modal parameters of the structure identified through input–output techniques (N4SID) in occurrence of seismic events, and through consolidated output-only techniques (SSI) in the periods between two subsequent events.