Numerical Analysis of the Seismic Response of Underground Steel Storage Tanks

The seismic behaviour of underground structures is generally satisfactory compared to the above-ground ones. However, despite of the buried structure confinement, in recent strong seismic events some underground structure as tunnels, pipelines and tanks suffered high damage; for this reason, a strong effort is focused to evaluate the seismic vulnerability of these structure and to give codes instruments to the designers. Concerning the underground water and oil storage tanks, in literature there is no indication on their seismic vulnerability. Starting from the previous experiences in the seismic analysis of above ground industrial equipments and in the seismic analysis of tunnels in soft soils, an integrated geotechnical and structural approach to underground industrial equipment is under development. In particular, attention is focused on the influence of fluid-structure and structure-soil interactions on the overall dynamic response. In this paper, an overview of case histories of post-earthquake damages of underground tanks is reported. Design guidelines and construction process are analyzed. Preliminary seismic analysis of sample underground steel tanks are carried out under simplified assumptions and described in order to point out key aspects of the problem. Results are reviewed in order to identify critical issues of the soil/structure/fluid interaction during the seismic event. An introduction to advanced numerical codes able to perform reliable interaction analyses using real strong motion records is given.