Evaluation of performances and reliability of a wavelet based modal parameter estimation method applied on the modal identification of the Meazza stadium grandstands in Milan

Structural monitoring is a crucial aspect for the safety management of large civil structures. A vibrationmeasurement-based monitoring system allows to estimate the structure's modal parameter and their change in time which is an indicator of possible damages. Operational modal analysis is the proper tool to this prupose, allowing a continuous monitoring of the parameters evolution with no needs for external excitation. A reliable modal analysis technique is therefore fundamental: in this paper a wavelet based modal parameter estimation method is analyzed. The method has been adopted in the modal parameters estimation of the grandstands of the G. Meazza stadium in Milan. It is a famous huge concrete structure composed of three different sub-structures built in different decades: the stadium can host about 80000 people. The Department of Mechanics of Politecnico di Milano since summer 2003 looks after the vibration monitoring of the Meazza stadium: measurement are available for different sorts of event, such as big concerts and important football matches and also a traditional modal analysis of one of the grandstands has been performed, loading the structure with an inertial electromechanical shaker. This allows to compare the wavelet based modal parameter estimation results with those from more commonly adopted methods such as the Least Square Complex Exponentials (LSCE, Prony's solution) and the Poly Reference Least Square Frequency Domain (known as POLYMAX), not only with unknown ambient excitation but also with a known one.