Nonlinear earthquake responses of unanchored cylindrical liquid storage tanks on flexible soil

A sophisticated and versatile finite-element model of the nonlinear behavior of unanchored cylindrical liquid storage tanks on flexible soil is proposed and applied for nonlinear earthquake response analysis of the system. The tank is modeled using shell finite elements with material and geometric nonlinearities. The hydrodynamic pressure is represented by acoustic finite elements. The effects of the base uplift are considered by nonlinear springs with negligible and large stiffness coefficients in tension and compression, respectively. The flexible soil is modeled using mechanical springs and dashpots. The effects of base uplift and soil flexibility are examined for typical unanchored tall and broad tanks on flexible soil with various shear-wave velocities. It is observed that the structural responses and hydrodynamic pressure, including the convective pressure of an unanchored tall tank on rigid/flexible soil, are significantly influenced by the base uplift. Although the base uplift in a broad tank is not as large as that in a tall tank, the structural responses and hydrodynamic pressure of an unanchored broad tank can be different from those of an anchored system. However, the convective pressure of the broad tank is not significantly affected by the base uplift. The earthquake responses of the system are principally influenced by the horizontal component of the earthquake ground motion rather than the vertical component.