Benchmark Analysis of Seismically Induced Fluid-Structure Interaction in Liquid-Containing Tanks with Insufficient Freeboard

Parameters of interest in the seismic analysis of liquid-containing tanks include reaction forces, slosh heights, and peak wall pressures. Numerous references including Section 7.4 of ASCE 4 have simplified expressions for wall pressures, overturning moments, and slosh heights for tanks with excess freeboard. For tanks with insufficient freeboard, less guidance is available. As an example, ASCE 4 requires that if tanks have insufficient freeboard, the liquid level must be lowered or the tank roof and wall must be designed to withstand the impact of the sloshing fluid. However, ASCE 4 does not provide specific guidance on evaluating the impact of liquid with the tank roof. The present study evaluates seismically induced fluid-structure interaction in flat-top and domed tanks with insufficient freeboard using the explicit finite element program MSC.Dytran® and the results of the study are compared to approximate solutions. For the systems considered, the study shows that the peak wall pressures in the domed tank are nearly the same as for a vertical-walled tank with excess freeboard. However, for the flat-top tank, the peak roof pressures are significantly higher than predicted using the approximate methods. In all cases, peak wall pressures lower in the tanks are unaffected by local roof or dome interactions.