Operational modal Analysis of the “Guglia Maggiore” of the “Duomo” in Milano

Every city has its own symbol, its very heart. In Milano this symbol, with its six centuries of history, is the Duomo. One of the most impressive buildings in Italy, this unique Gothic cathedral continues to awe citizens and travelers with its timeless beauty. A fascinating characteristic is the building process of the Duomo: to date the church is in fact technically still under construction. The conservation of the Duomo is an activity which will never end which requires a continuous upkeep. It involves various phases: the observation, the studying of the decay phenomena and their monitoring, the settlement and the realization of a solution which prevents the time from damaging the monument. There is then need to provide people in charge of the Duomo’s Restoration with tools capable to describe the behavior of this structure as time goes by. Among a wide number of static parame-ter monitoring, another instrument is the use of modal analysis. This paper describes the dynam-ic analysis that has been performed inside the restoration plan of the Guglia Maggiore aimed at providing a description of the dynamic behavior of this work of art. However the features of the Duomo make it difficult to excite the structure under test with an imposed force. In this work the identification of the modal parameters of the Guglia Maggiore of the Duomo has been per-formed by means of Operational Modal Analysis, that is without knowing nor controlling the input excitation. Special attention has been paid to the influence of environmental conditions, i.e. wind, people coming and going (daytime and nighttime), on the response of the structure.