Ambient vibration tools supporting the model-based seismic assessment of existing buildings

The technological advancements of the last decades are making dynamic monitoring an efficient and widespread resource to investigate the safety and health of engineering structures. In the wake of these developments, the thesis proposes methodological tools supporting the seismic assessment of existing buildings through the use of ambient vibration tests. In this context, the literature highlights considerable room to broaden the ongoing research, especially regarding masonry buildings. The recent earthquakes, once again, highlighted the significant vulnerability of this structural typology as an important part of our built heritage, remarking the importance of risk mitigation strategies for the territorial scale. The thesis builds upon a simplified methodology recently proposed in the literature, conceived to assess the post-seismic serviceability of strategic buildings based on their operational modal parameters. The original contributions of the work pursue the theoretical and numerical validation of its basic simplifying assumptions, in structural modelling – such as the in-plane rigid behaving floor diaphragms – and seismic analysis – related to the nonlinear fundamental frequency variations induced by earthquakes. These strategies are commonly employed in the seismic assessment of existing buildings, but require further developments for masonry buildings. The novel proposal of the thesis takes advantage of ambient vibration data to establish direct and inverse mechanical problems in the frequency domain targeted at, first, qualitatively distinguishing between rigid and nonrigid behaving diaphragms and, second, quantitatively identifying their in-plane shear stiffness, mechanical feature playing a primary role in the seismic behaviour of masonry buildings. The application of these tools to real case studies points out their relevance in the updating and validation of structural models for seismic assessment purposes. In the light of these achievements, a model-based computational framework is proposed to develop frequency decay-damage control charts for masonry buildings, which exploit ambient vibration measurements for quick damage evaluations in post-earthquake scenarios. The results of the simulations, finally, highlight the generally conservative nature of ambient vibration-based simplified methodologies, confirming their suitability for the serviceability assessment of existing masonry buildings.