Titolo della tesi: Inerter-based hybrid control systems for the seismic protection of steel storage tanks with floating roof
The condition of industrial plants is very complex in relation to natural events such as earthquakes.
The release of the hazardous materials, explosions, fires, the possibility of damage propagation to
neighbouring areas and, not least, human injuries and losses represent only some of the serious consequences associated with an accident involving a plant, hence the name of major hazard industrial
plants. The large number of connections and components, combined with their inherent vulnerability and usual arrangement in series, implies that the failure of the entire system can arise from the
failure of the single element. Among all the components of industrial plants, cylindrical steel storage
tanks are widely spread and play a primary role when subjected to seismic hazard, since they suffer
of many critical issues related to their dynamic response such as high convective wave height and
base shear force. Within this framework, the growth of interest towards the seismic response of
liquid storage tanks, their typical types of damage and the applicability of the main passive control
techniques, i.e. Base Isolation Systems (BIS), Energy Dissipation Systems (EDS) and Tuned Mass
Damper Systems (TMD), can be understood. The seismic base isolation has been widely studied,
both in passive and semi-active control. Nevertheless, the onset of the deformable layer, which can
experience high displacements, the extent of the isolation period which may draw a value comparable
to the sloshing modes period, implying the incapability of controlling the convective response
and the lack of efficacy against impulsive actions limit its use. With the purpose of preserving BIS,
the employment of a supplemental TMD has been widely explored in the literature, with the resulting
definition of a Hybrid Control System (HCS), involving both a BIS and a TMD. In the recent
years, a two-terminal device, named inerter, able to establish a difference in acceleration between
its two terminals, so to produce an amplification mass effect, making the inertial mass much greater
than the gravitational mass, has been proposed. This feature makes its use particularly interesting
in passive vibration control. In fact, an inerter-based system, named Tuned Mass Damper Inerter
(TMDI), with high inertial mass ratio can be obtained, adding an inerter device to a conventional
TMD. In this thesis work, a HCS, endowing a base isolation system BIS with a TMDI, is proposed
for the protection of steel storage tanks from severe structural damages induced by seismic events.
The adopted BIS is realized with spring and damper elements, whereas the TMDI is realized with
a tuned mass damper connected to the ground by the inerter. The developed mechanical model
consists of a MDOF system, which considers the impulsive and convective modes as well as the
TMDI dynamics. An optimal design problem is tackled, making use of a multi-objective approach,
with the scope to mitigate simultaneously the convective and impulsive response of the storage tank.
A zero mean white noise excitation is assumed as input in the optimal design procedure. Once the
HCS is optimally designed, a systematic investigation of its seismic effectiveness is reached through
parametric analysis. Modal parameters and frequency response functions are discussed as well as
time histories. Comparisons with other design methodologies are shown. Moreover, limit cases and
alternative control systems are discussed. A literature case study comparing the effectiveness of the
proposed optimally designed HCS with traditional base isolation is illustrated and performances
are assessed through stochastic excitation and natural earthquakes. in the end, the influence of the
presence of the floating roof on the performance of the provided HCS is discussed.