Comparison Between Seismic Responses of Anchored and Unanchored Cylindrical Steel Tanks

Abstract eng:
Many above-ground cylindrical steel tanks have borne serious damages during the past earthquakes. Therefore understanding and forcasting their seismic behavior have attracted numerous researchers. These tanks are mainly classified into two types, i.e. anchored and unanchored. Of course a large number of existing tanks in oil and petrochemical industries are of the second type which has been more susceptible to damage in the past earthquakes. The seismic responses of above-ground liquid-filled steel tanks have been investigated using comprehensive finite element techniques. Both fluid-structure and soil-structure interactions have been employed in order to take the actual behavior of structure into account. In numerical study, finite element models have been used for three tanks with height to diameter ratios (H/D) of 0.33, 0.75 and 1.5, in which considering a liquid level of 90% of the height of cylinder, in an attempt to compare between seismic responses of unanchored and anchored tanks. Several factors are involved in the analysis of such tanks due to uplifting, material yielding, soil-tank interaction and large-amplitude free surface sloshing. It has been shown that the effects of the above mentioned factors for tanks of the two kinds, differ from each other. For instance in unanchored tanks, uplifting reduces the hydrodynamic pressures, whereas this phenomenon does not occur in anchored tanks. Also for broad tanks, both anchored and unanchored types show almost identical free surface sloshing, whereas it should be noted that this is not the case with tall tanks which appear to be more sensitive to sloshing phenomenon.

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