TECNICHE DI IDENTIFICAZIONE MODALE PER L’ANALISI STRUTTURALE. L’evoluzione del comportamento dinamico di un edificio scolastico in cemento armato soggetto a miglioramento sismico

This work deals with the structural retrofitting of a Reinforced Concrete (RC) building school and illustrates the results of a structural monitoring campaign performed on this. The examined school building presents typical and specific vulnerabilities of Italian building stock - of which RC buildings currently represent the greatest portion - mostly built in 60’s and 70’s Because of its vulnerabilities, the structure was subjected to a deep structural retrofitting intervention based on increasing of original columns cross-sections with introduction of new longitudinal steel bars and stirrups, and application of shear reinforcement on beams using Fiber Reinforced Polymers (FRP). The building was monitored using Operational Modal Analysis (OMA) technique, that offers the possibility of describing structural dynamics at small vibration amplitudes in real operating conditions with unknown excitation inputs. The long-term Ambient Vibration Survey (AVS) - performed before, during and after the works, in a campaign lasted one year - highlighted the increasing of building performance in terms of natural frequencies following the retrofitting works. Moreover, the paper shows how infill panels influence the dynamic response of this typical RC structure. This relevant data collection, in addition to confirm the potentil of OMA technique in gathering the real structure behavoiur, could be very helpful in the calibration of other similar retrofitting interventions.