A numerical procedure to estimate seismic fragility of cylindrical ground-supported steel silos containing granular-like material

The paper presents a study on the evaluation of seismic fragility of cylindrical ground-supported steel silos intended for storing solid material. Silos are a key facility in industrial processes. For example, cylindrical steel silos constitute the main structural component for several industrial activities, such as the ones aimed at the production of food and beverage, and seismic actions can cause high economic losses and long functionality interruptions. Thus, the main goal of this paper is to propose a numerical procedure aimed to assess the seismic fragility of different cylindrical steel silos, accounting for varying geometries and service conditions (i.e., filling level of granular-like material), and observing different failure modes. In detail, a set of smooth steel silos was selected, considering different geometrical configurations (i.e., varying from squattest to slenderest structures). Different service conditions were simulated, with the aim to observe the behaviour of empty and filled silos (30%, 60%, and 90% of filling degree with respect to the maximum capacity). For each configuration, a detailed numerical model was developed under proper boundary conditions, adequately simulating the shell structure, the solid material inside, and the interactions between them. After validating the numerical models against existing literature data, three different failure modes were identified and assessed, accounting for the most recurrent post-elastic buckling type (i.e., elephant foot) and considering the possible occurrence of the elastic ones (i.e., diamond or similar shape failures at the middle and top of the structures). Both static and dynamic analyses were performed to identify the most probable failure modes and evaluate the probability of exceeding each one. As the output of the proposed approach, the seismic performance of each silo under a specific limit state was provided in the form of fragility curves. The results highlight some novel aspects, starting from the role that service conditions assume in the silos seismic performance up to the possible differences in terms of failure modes for different silos geometrical structural configurations.