314 E. Mola et al. This was the case for the Allianz Tower: both the project Validator and the Owner agreed on the opportunity of carrying out dynamic tests at the end of construction: it was decided to use the Operational Modal Analysis method, so that only the environmental excitation would be exploited to derive the modal properties, with no need to move and install large tools at the top of the building to provide additional forcing, which would have been required for Experimental Modal Analysis, [2]. The results of the dynamic tests were used to validate the finite element model of the building that had been implemented in the structural analysis software MidasGen. Moreover, since a peculiar architectural and functional feature of the Allianz Tower remains in the external viscous dampers at the base of the struts, which are designed to provide additional damping under wind loads, i.e. in service life conditions, for very low levels of vibration, the OMA tests in this case also provided insight on the actual efficiency of those devices: the tests were carried out before and after the installation of the dampers, so that it was possible to experimentally derive the modal damping in service life conditions with and without the contribution of the dampers, thus obtaining important data for the validation of their design and installation process. 32.2 Description of the Structure The Allianz Tower occupies the center of the redevelopment site of the former exhibition center in Milan, called CityLife, in front of the building that housed the old Sports Palace, which overlooks Viale Boezio. The building, which is going to be used as the headquarters offices of Allianz in Italy, has a height of 202 m above the ground level of the main plaza and 207 m above the street level. Below the ground level, one underground level connects the tower with the underground shopping area as well as the metro station, and two other underground levels are devoted to mechanical use (Fig 32.1). Fig. 32.1 (a) Masterplan of the CityLife Development; (b) Architectural rendering of the three CityLife Towers (Allianz Tower is on the right), (c). The topped-out Allianz Tower
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