During an earthquake event, the loss of function of critical infrastructure systems such as petrochemical and water tanks represents significant risk to life and increases the scale of economic loss. Combined tanks are commonly built with a containment vessel consisting of a truncated cone with a superimposed cylindrical cap and are widely used to store water under a specific pressure which allows for easy water distribution. The design of water tanks is usually based on the American Water Works Association standards (AWWA D100-05) [1] which includes a detailed design procedure for liquid-storage cylindrical tanks under vertical excitation. However, no direct seismic design procedure is provided for vertically excited combined tanks. The proposed study aims at identifying the dynamic characteristics of vertically excited liquidfilled combined steel tanks. Analysis is conducted numerically using a coupled finite-boundary element formulation that takes into account the encountered fluid-structure interaction. An equivalent mechanical analog is developed to simulate the seismic response of vertically excited liquid-filled combined tanks. The liquid-shell continuum is idealized as rigid and flexible mass components. The proposed model provides a simplified tool for prediction of the seismic forces acting on liquid-filled combined tanks subjected to vertical ground excitation.
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