Earthquake simulator studies of cylindrical tanks

Abstract

An experimental investigation on the seismic response of ground-supported, cylindrical metal tanks is described. Experimental and analytical research by other investigators over the past forty years has provided a firm basis for the computation of free- and forced-vibration behavior in ideal liquid-filled circular cylindrical shells with a variety of elementary support conditions. However, the actual seismic behavior of ground-supported tanks has not been known, and practical design methods necessarily have been based on simplifying assumptions. The present results provide the first opportunity for rational evaluation of seismic design assumptions, and suggest theoretical developments which would enhance the realism of refined seismic analyses. The aluminum scale model discussed here, 12 ft in diameter and 6 ft high, represents a 36-ft diameter steel prototype. It was tested, in anchored and unanchored base configurations, under action of a time-scaled El Centro, 1940, earthquake with peak acceleration of 0.5 g, using the Earthquake Simulator Facility of the University of California, Berkeley. Stresses and displacements of the model, in both anchored and unanchored conditions, were dominated by effects of “out-of-round” response in higher-order circumferential modes, a result which is not predicted by current seismic analysis theory, and which contradicts basic assumptions of current design practice. The experimental observations are discussed in relation to dynamic analysis theory, practical design methods, and the history of tank performance in past earthquakes.