Mitigation of elephant-foot bulge formation in seismically-excited steel storage tanks

This paper summarizes the findings of the first phase of a comprehensive study aimed at mitigating the effects of earthquakes on steel liquid storage tanks using hybrid fiber reinforced polymer laminates. In assessing the safety of tanks under seismic loading, the capacity of the shell against buckling must be evaluated. There are two types of shell 'buckling': membrane and elastic-plastic. Although the latter is not accounted for in most codes, it may limit the seismic design especially at higher values of total liquid pressure. The elastic-plastic buckling capacity is nearly depleted when the ratio of total-to-hydrostatic pressures is equal to the design factor of safety. In order to relief the shell from excessive hoop stresses, it is suggested to apply hybrid fiber reinforced polymer laminates, with the fibers aligned along the circumference of the shell. The combined system of carbon and glass fibers must circumvent the galvanic reaction with steel, in addition to exhibiting thermal balance and appropriate durability properties. It has been confirmed theoretically that the proposed system is viable for reducing seismic vulnerability of tanks; experimental verification is underway. (author)