Vibration control of steel liquid storage tanks equipped with Inerter-based isolation systems

Base isolation represents a very widely used strategy to mitigate the effects of earthquake excitation on structures. However, it can induce high displacements between the isolation layer and the ground, which may cause serious damage, and even heavy and dangerous consequences in case of industrial components. Among them, big steel tanks for storage of petroleum or other chemical products, should be considered very carefully. Moreover, isolation technique doesn’t seem to be effective in the control of the sloshing modes, due to the length of their periods of vibration. This fact can imply severe negative effects on the free surface of the storage tank, where the sloshing wave can exceed the upper limit of the tank, overtopping it, or inducing breaking on the floating roof. Moving from the results available in the Literature, in which the introduction in civil applications of a two terminal device, named inerter, able to generate an inertial mass much greater than its gravitational mass, is proposed; the force produced by the inerter is proportional to the difference of acceleration between its terminals. This work concerns the evaluation, through numerical models, of the seismic performance of a passive base isolation system involving a ground inerter system, called IBIS in the following, connecting the isolation layer of a steel liquid storage tank to the ground. The model considered in the numerical analysis consists in a reduced 2DOF linear system. The first degree of freedom is represented by the first sloshing mode; the second is relative to the base isolation system, whose mass includes the basement, the tank and the impulsive component of liquid mass. The aim is to gain a reduction of the response in terms both of isolation layer displacement and of sloshing height. The effectiveness of the control strategy proposed has been evaluated considering both a random white noise process and earthquakes (near-fault and far-field) as base input, achieving strong reduction of the response, in terms of sloshing height and isolation displacement.