Seismic vulnerability assessment of steel storage tanks protected through sliding isolators

An adequate seismic protection of steel storage tanks of industrial, chemical and petrochemical plants is essential since potential consequences of failures, besides the economic losses, can be catastrophic for the environment and for people living nearby. Among the most common damages suffered by steel tanks in recent earthquakes, there are the elephant-foot-buckling of the perimeter wall and the tanks' uplift or overturning. Due to the uncertainties related to the estimation of the mechanical properties of filled tanks and related seismic loads (i.e. dynamic overpressures generated by the content), conventional design approaches may lead to unsafe or, on the contrary, oversized solutions. Among effective alternatives, base isolation through Curved Surface Slider isolators (CSSs) offers some valuable advantages like high load bearing and displacement capacity with compact dimensions, independence of the oscillation period on the supported mass, and minimisation of torsional effects. Despite being neglected by most common commercial FEM codes, as a drawback, recent studies pointed out that the initial peak of friction force at CSSs' motion breakaway can lead to significantly increased lateral deformations and accelerations of the superstructure. Within this framework in this study, a refined numerical model is developed in OpenSees FEM code, and an exhaustive parametric study is carried out to investigate the effect of the breakaway on isolated tanks providing some useful insights for the selection of the most suitable isolators.