The seismic behavior of ground-based liquid storage tanks under horizontal and vertical excitations has received considerable attention in the past two decades; however, most of these studies dealt only with the behavior of anchored tanks. Few attempts were made to analyze the complex behavior of unanchored tanks and models sought were either too simple to capture the basic response of such structures or too complicated by modeling many features at once. It is believed that the behavior of the bottom plate is a dominant factor in the analysis of the overall system. Also, based on past experimental tests, liquid sloshing has a more pronounced effect on the response of unanchored than anchored tanks. This research will conduct a comprehensive study to analyze the seismic response of unanchored tanks. The study consists of both theoretical and experimental investigations, and is divided to three major phases: 1. Nonlinear static and dynamic analyses of the response of the bottom plate of the tank under uplifting forces taking into account its nonlinear contact with the foundation, its large deformations, its inelastic response, its interaction with the underlying soil and its behavior under impact; 2. An analysis of the nonlinear response of the liquid, and an evaluation of the corresponding hydrodynamic pressures; and 3. An analysis of the coupled response of the shell, the liquid and the bottom plate under moderate to severe earthquake motions. The research will provide a comparison between theoretical results and observed experimental data to assess the accuracy and the reliability of the predicted response.
