Seismic fragility and dynamic behavior of atmospheric cylindrical steel tanks

The main purpose of the research carried out in the aim of this PhD dissertation has been the analysis of the dynamic behavior of on-grade cylindrical steel storage tanks. This has been done through two main research fields: the evaluation of tank seismic fragility and the analytical modeling of the tank dynamics when subjected to the ground acceleration. In the first part of the study, new fragility models have been proposed with the aim to overcome limits and week points of past researches. For this purpose, a large dataset of information on failures of atmospheric tanks during past earthquakes has been collected. Two sets of Damage States have then been used in order to characterize the severity of damage and the intensity of liquid releases. Empirical fragility curves have been fitted by using Bayesian regression. Different generalized linear models have been employed in order to investigate the effects of tank aspect ratio, filling level and base anchorage. Moreover, the effects of the interaction between these critical aspects is included in fragility analysis. The second section of the present PhD study has focused on the mechanical modeling of unanchored tanks dynamic. An investigation on inertial and centrifugal forces in the context of the interaction between tank rocking and translational motions is proposed. The simultaneous dynamic equations of a 2DOF model have been solved through a numerical software and results have been compared with those of experimental tests. Moreover, employing the dynamic properties governing the tank rocking-bulging motion into the 2DOF model equations, a simplified method to determine the tank bulging response and the measure in which it is reduced by the rocking appearance is provided. Validation of the proposed analysis is conducted comparing its results with those computed through an Explicit Finite Element Analysis on a sample tank.