High resolution operational modal analysis of Sant’Agata del Mugello in light of its building history

Abstract

The building history of a cultural heritage building and the after-effects induced by extreme loads such as earthquakes have a durable impact on its modal parameters. This article aims to discuss the peculiarities of some modal parameters extracted from ambient vibration measurements in light of the complex history of Sant’Agata del Mugello. The Romanesque church located in the Mugello basin (Tuscany, Italy) suffered from many earthquakes, at least from 1542. In this context, we carried out two dense ambient vibration campaigns in March and June 2019. We extracted each mode’s natural frequency, mode shape, and damping using the Enhanced Frequency Domain Decomposition. We identified ten modes. Some modes highlight structural singularities related to the building history of the church: rocking of the base of the bell tower; phase opposition between the bell tower and the nave; bending of the walls of the nave. Since the instrumentation benefited from a vast number of recording positions (83), we tested the impact of the sensor placement strategy on the resolution of the identified modal parameters in the specific case of Sant’Agata del Mugello. The resolution of the higher-order modes decreases strongly in case of degraded sensor placement strategy impacting the dynamic analysis of the church.