Ambient vibration testing of existing buildings aimed to seismic assessment: experiences in Liguria

Ambient vibration tests (AVTs) provide valuable information about the dynamic behavior of existing buildings. Their use is well established in Structural Health Monitoring (SHM) applications to detect modification in structural behaviour after ageing, damage and retrofitting, and surely to calibrate or build numerical models aimed to the seismic assessment. Moreover, vibration-based methodologies assume great relevance within seismic mitigation strategies to prioritize retrofitting actions at urban scale. In this context, the Italian Department of Civil Protection developed the Seismic Model from Ambient Vibrations (SMAV) which relies on modal parameters extracted by AVTs to evaluate the operational level of strategic buildings following a seismic event. Within the application of the previous procedure, this work presents an extensive measurement campaign carried out in Liguria Region in collaboration with Geamb S.r.l in which full-scale AVTs have been performed on seven strategic buildings located in the provinces of Savona and Imperia. The structures under test, four made by reinforced concrete and three by unreinforced masonry (URM), differ greatly for dimensions, constraints and complexity. For each building system identification is carried out using several output-only techniques comparing the results in terms of natural frequencies, damping ratios and mode shapes. Since the measurement chains have been planned according to the assumption of diaphragms in-plane rigidity required by SMAV, the paper investigates how this can affect the accuracy of identified modal parameters and discusses some verification tools.