Modal identification of storage racks for cheese wheels

During the Emilia-Romagna earthquake (2012), a great number of steel racks used to store cheese wheels collapsed, causing a non-negligible damage to the Italian economy. Therefore, for similar structures that survived and are in service, a deep investigation towards the assessment of their effective safety is required. In the seismic analysis of these frames, the mechanical constraint acting onto the racks due to the reinforced concrete sidewalls, possible nonlinearities exhibited by the base-plate joints and the in-plane restraint provided by wooden boards that connects adjacent columns should be carefully modelled to ensure realistic design results. In the paper, an experimental activity, based on suitable modal identification techniques, is presented to capture the dynamic behaviour of these peculiar structures. The scope is to collect data useful to calibrate numerical finite element models in order to accurately define the aforementioned unknown parameters. Furthermore, a few numerical models based on ideal restraints are herein discussed stressing out non-negligible differences in terms of expected seismic and static response.