Evaluation of the response of historical structures fitted with seismic-isolation

The paper highlights the performance of the seismic isolation devices installed on retrofitted buildings in reducing the seismic response when subjected to earthquakes. Two buildings from the beginning of the XXth century in Bucharest are chosen from many more, monitored over the city area. We discuss the response of these base-seismic isolated structures, relying on good quality data acquired from the recent strong earthquake (3 November 2022, MW = 5.0). Elastic response spectra computed from recordings at two levels of each structure are used, placed under and right above the isolating layer. At one building, the existence of previous recordings and the particularity of the sensors allow a comparison with the other two relatively recent medium-intensity earthquakes. The assessment is carried out in terms of maximum acceleration amax, measured at certain levels in each structure, spectral acceleration amplitude SAmax, and spectral-peak corresponding period. We find that the base-isolation methodology is effective in reducing the response of the building right above the isolating layer, an observation valid for both structures, all components of the recordings, and spectral acceleration values. Moreover, the outcomes from the modal evaluation performed prior to rehabilitation and the seismic isolation process are presented by pointing out a higher newly acquired fundamental period of the isolated structures.