Approach to Cylindrical Steel Tank Design to Accommodate Sloshing Effects

The term "sloshing effects" describes the impact of a seismic event on a container and its liquid contents. To prevent the accidental release of the contents of a container, container design must simultaneously accommodate the impulsive force of an earthquake on the rigid components of the container and forces generated by the resulting convective wave confined inside the container. California Accidental Release Prevention (CalARP) has issued guidance regarding minimum design parameters for this situation. CalARP's primary solution is to completely confine the convective wave within the container's freeboard, the space between the maximum static surface of the liquid and the roof of the container. In the case of potable water, this solution has undesirable side effects on water quality, system capacity, and corrosion prevention. CalARP's secondary solution is to accommodate the uplifting forces of the convective wave on the roof and the combined lateral impulsive and convective forces on the structure in the design of the tank. The objective of this paper is to develop an approach for explicit calculation of the lateral and uplifting forces of the convective wave and their superposition with respect to impulsive seismic forces. This approach is currently being employed in the design of a cylindrical steel potable water tank in California. The approach has been tentatively approved by the California Department of Public Health pending final design, and the eventual owner of the tank desires to incorporate the approach into the agency's design standards. Successful application will meet CalARP requirements, reduce construction materials, improve water quality, maximize system capacity, and reduce corrosion. In addition, application to seismic retrofit of similar water tanks may result in similar benefits and extend the infrastructure life cycle.