SEISMIC MONITORING OF BUILDINGS WITH BASE ISOLATION

The seismic monitoring of buildings is important for two fundamental reasons: - evaluate the possible dynamic behavior of these structures during earthquakes; - gain experience on the general seismic behavior of the structures so that the experience and the database can be used in the future for design and analysis. The results of previous efforts in seismic monitoring of the structures have facilitated the devel-opment of a database, which in turn was used in the creation of new formulas and reference values for the estimation of the fundamental periods of the structures and the percentage of crit-ical damping from use during dynamic analyzes. The database is very well supplied with data on traditional buildings, but there is still not enough data for buildings isolated at the base. Some different structures with seismic base isolation have been monitored during recent strong earthquakes in Italy, namely Amatrice earthquake (2016/08/24, Mw=6.0) and Norcia earth-quake (2016/10/30, Mw=6.5). For the structure under examination, amplification phenomena have been noticed, up to about twice the accelerations on the superstructure, for very low energy value inputs. In these cases, however, it is noted that the amplified accelerations are extremely small, and very far from be-ing able to damage the structure. Records from the ENEA permanent accelerometric network, installed on the structure under examination, and the tests carried out on the same isolators used for the qualification tests of the devices mounted below the analyzed structure, permit to describe the behavior of the isolators in terms of force and displacement defining two non-linear laws, derived from experimental data.