"Role and perspectives of modal identification in rapid and permanent structural monitoring after an earthquake."

Structural identification based on experimental data coming from rapid and/or permanent monitoring is continuously increasing its relevance in the process of the structural safety assessment. The paper discusses the direct and inverse problem of structures subjected to base excitation. Recent results in time domain modal identification are summarized for their relevance in the treatment of data coming from either rapid testing or permanent monitoring activities realized after the 2009 L’Aquila earthquake for two case studies. In the first one, the vibration measurements acquired in a two-day testing campaign on a damaged reinforced concrete building belonging to the Engineering Faculty of the University of L’Aquila have been used to directly compare the identified modal features with a modal model constructed by finite elements, representative of the structural behavior of the building in the early post-earthquake conditions. In the second one, the seismic response obtained through a permanent structural health monitoring system deployed on a monumental masonry building, the Basilica of S. Maria di Collemaggio, has been used to extract the modal parameters which compared with results coming by a finite element model, have furnished valuable information to evaluate the effectiveness of the temporary scaffolding structures. The study evidences that the reference-based combined deterministic-stochastic subspace identification of structures heavily damaged by earthquakes is a valuable tool to insight into noisy data acquired in difficult operational conditions. Finally, the specific technology developed along the research, for easy structural response measurements, is also presented, and its peculiar characteristics and drawbacks are finally discussed.