Behavior of large tanks during seismic events has implications far beyond the mere economic value of the tanks and their contents. If, for instance, a water tank collapses, as occurred during the 1933 Long Beach and the 1971 San Fernando earthquakes, loss of public water supply can have serious consequences. Similarly, failure of tanks storing combustible materials, as occurred during the 1964 Niigata, Japan and the 1964 Alaska earthquakes, can lead to extensive uncontrolled fires and pollution of surrounding areas. Therefore, it is important to consider seismic forces in the design of these tanks.
Several sophisticated techniques to analyze unanchored tanks have been developed in the past. These techniques are not available for the industrial community mainly because they require expensive computers and extensive knowledge of finite element techniques. Thus, new tanks are designed using the available simple, but deficient, design standards, which make these tanks susceptible to failure during strong ground motions.