Effects of people occupancy on the modal properties of a stadium grandstand

It is well known that of people standing or sitting on a structure can change the dynamic behavior of the structure itself. Particularly, when a significant number of people are occupying a structure, high variations of non-dimensional damping ratios and natural frequencies are often experienced. The extent of these changes depends not only on the number of persons, but also on the properties of the empty structure and on people position and postures. This work analyses the effects of the presence of people on a grandstand of the San Siro stadium during some football matches and concerts. These effects are analyzed in terms of changes in modal parameters and amplitudes of vibrations. The impact of the number of people present on the structure on its dynamic behavior is also analyzed. The first results of an analytical approach, based on a FE model of the stand and a lumped parameter model of the people, to foresee the effect of people presence on stadia grandstands, is proposed in the end of the paper. The ob tained results show that if an accurate model of the structure and detailed description of the stand occupancy are available the predicted results are in good agreement with the experimental evidence