Ambient vibrations-supported seismic assessment of the Saint Lawrence Cathedral’s bell tower in Genoa, Italy

Abstract

Post-earthquake damage surveys systematically highlight the seismic vulnerability of monumental structures, calling for simple assessment procedures to address the design of effective retrofitting interventions. The structural complexity characterizing monumental structures, however, makes a reliable prediction of their seismic response a relevant challenge of engineering interest. Ambient vibration tests (AVTs) provide valuable support to achieve such a task, improving the knowledge of the actual dynamic behavior of the structure and, consequently, the reliability of the seismic assessment. In this context, the paper illustrates the integration of AVTs outcomes with the evaluation of the seismic performance of historic masonry structures by presenting the comprehensive application to a case study, the bell tower of the Saint Lawrence’s Cathedral in Genoa, Italy. The research combines the assessment of the global seismic response of the tower, investigated through a simplified mechanical model, with the local verification of the pinnacles placed at its top, referring to a displacement-based approach on a macro-block model. An extensive ambient vibrations measurement campaign carried out in May 2020 allowed for a comprehensive operational identification of the bell tower and its pinnacles, clarifying the ongoing dynamic interaction with the main body of the church. This valuable information was successfully employed, first, to accurately reproduce the actual constraint conditions induced by the church on the bell tower, a determining factor in the modeling of its global seismic response and, second, to reliably quantify the seismic amplification caused by the tower filtering effect to be used as the seismic input for the local verification of the pinnacles.