Refined Numerical Modelling of Steel Storage Tanks Implementing Sliding Isolators

In recent earthquakes, besides the sloshing of the content and the failure of piping systems, among the most common damages suffered by traditional fixed-base steel tanks, there is the uplift, in worse cases the overturning, and the “elephant-foot-buckling” of perimeter walls. Over possible solutions, base-isolation of tanks through sliding isolators offers some valuable advantages like the high load-bearing and displacements capacities with compact dimensions, and the independence of the oscillation period on the mass of the supported tank. As a drawback, recent studies pointed out that the initial peak of the friction-force that precedes the sliding motion within the isolator can cause significantly increased lateral deformations, and accelerations of the superstructure. However, this phenomenon, known as “breakaway effect” is not accounted for in commercial FEM codes leading to potentially unsafe design simulations. Within this framework, a refined modelling approach developed in OpenSees software is proposed in this paper and exploited to carry out a wide parametric study. The results prove that, with respect to traditional fixed-base tanks, the insertion of the sliding isolators always leads to improved safety levels against the buckling of tank walls. On the contrary, especially in case of high-friction isolators under severe ground motions, the breakaway has a negative effect on the tanks uplift of their overturning.