Seismic Performance of Storage Steel Tanks during the May 2012 Emilia, Italy, Earthquakes

Field observations following the May 2012 Emilia, Italy, earthquakes have revealed the seismic vulnerability of storage steel tanks typical of the past Italian design practice, highlighting structural deficiencies observed during previous events in other areas and mostly related to lack of structural seismic design and detailing, lack of redundancy, and inadequate anchorage design and execution. Damage was disproportionately high, considering the moderate size of the events (MW=6.11 and MW=5.96 on 20th and 29th May, respectively). Failure modes observed are reported and classified. Comparison is provided with the results of high-definition finite element (FE) dynamic simulations, performed on tanks representative of those inspected. Numerical analyses, accounting for material and geometrical nonlinearities, at the element level, as well as for fluid-structure interaction through highly nonlinear methods, were able to capture the stress/strain concentrations that caused them to collapse. Elephant’s foot and diamond buckling induced by hydrodynamic pressures as a result of inertial forces imparted during the earthquakes were reproduced, as well as shear-buckling failure of leg-supported tanks or sliding of unanchored systems.