Vibration monitoring of the G. Meazza stadium in Milano during concerts and football matches

Starting from summer 2003 special attention was devoted to the G. Meazza stadium in Milano, to investigate some vibration problems related to movements of people attending big events. At the beginning attention was mainly paid to a few measurement location inside the stadium and a number of points in the nearby buildings in which significant vibrations were perceived during particular events, especially concerts. Measurements taken in the buildings showed that in certain exhibition moments a significant vibration level was attained, at a single well defined frequency. It seemed that this condition could be described in terms of a narrow band excitation coming from the stadium which locked on to a building resonant frequency. The vibration recorded inside the stadium in the same moments showed more or less the same frequency content recorded outside, and this aspect has been considered worthy of further analysis. The vibration levels reached on the stadium stands posed a series of problems in terms of structural behavior. The G. Meazza stadium is a well famous huge concrete structure, capable of around 80000 seated places during football matches, and a similar number in other occasions, such as concerts. The stands are cantilevered and this fact, as evidenced by literature constitutes one of the main worries due to the jumping action of people. The stadium is composed of three different sub-structures built in different decades, from the late twenties up to the early nineties; each substructure is independent from the others and behaves differently when excited by the moving crowd. After the first tests, in summer 2003, other measurements were committed, to investigate the structure behavior and the leading mechanism due to the different kinds of events, not only concerts. To this purpose an important football match capable of fulling the grandstands and all of the 2004 summer concerts have been monitored, with some important aspects worthy being underlined: the same artist performed in the two subsequent years, singing the same songs which gave the mentioned phenomena of perceptible vibrations. Data gathered are still being analyzed to compare different forms of crowd-induced vibrations: particular attention is given to excitation and vibration repeatability under the same conditions (same songs or a goal). Some first steps towards a complete operational modal analysis have been moved too. These results will serve as a starting point for two main activities that are the design of a permanent monitoring system and a wide and reliable set of data creating a reference for tuning a fem model of the most critical structures through numerical analyses. The next paragraphs will follow this working law, presenting a summary of the developed activities, the main results, and possible future actions.