Long term operational modal analysis of a stadium grandstand to structural health monitoring purposes

In the last years an increasing interest has been devoted to all the topics related to security and safety of people. Particular attention has been paid to health monitoring of large civil structures hosting lot of people, like high-rise buildings and stadia. The vast scientific literature confirms the possibility to relate structural health to the evolution of modal parameters, often reaching the aim of localizing any eventual damage, a task otherwise impossible with different techniques. This paper shows a part of the long lasting project involving Politecnico di Milano in the setting up of a permanent health monitoring system at the G. Meazza stadium in Milan. As damage identification is related to changes of the modal parameters, the evaluation of their normal spread is fundamental to fix a threshold in order to identify possible worrying situations. This paper deals with the identification of the spread in the modal parameter estimation of one of the grandstands of the so-called 3deg ring of the G. Meazza stadium in Milan, setting up an automated operational modal analysis algorithm and analyzing a first set of data. Some ideas are gathered in order to identify the minimum number of identifications needed to have a robust estimation of the modal parameters.