Ambient vibrations for the assessment of the strengthening intervention of a masonry barrel vault

Vibration-based structural monitoring is a fundamental tool to assess the conditions of existing structures, in their real operating state. In particular, as concerns masonry buildings, although a large part of the Italian and European historical heritage is composed of vaulted structures, comparatively few papers in the literature are targeted to the study of the dynamic behavior of vaulted systems. The present work focuses on the application of vibration-based structural monitoring to a barrel vault of the Bussi Castle, located in Pescara, Italy, which suffered some damages as a consequence of the 2009 L'Aquila earthquake. Ambient vibration tests were carried out in the damaged state and after repair and strengthening of the vault for evaluating its dynamic behavior in both states. In either conditions, the modal parameters of the vault were identified using operational modal analysis techniques. The comparison of the modes in the two states, carried out with Modal Assurance Criterion index, clearly indicates an enhancement of dynamic behavior of the consolidated vault. In particular, a new index named Modal Symmetry Index is introduced. The index is based on a proper ratio between mode shapes to evaluate the improvement of the structural symmetry after the restoration interventions. The results confirm the effectiveness of the devised index to evaluate the strengthening interventions and, the potential of the structural monitoring to control the behavior of damaged vaulted masonry systems.