Non linear vertical-rocking isolation system: Application to legged wine storage tanks

Abstract

In the last 30 years, there has been a great development of seismic isolation systems. The most used areelastomeric type devices and frictional pendulum bearings. Although different, both types generate horizontalseismic isolation, but not vertical. This study presents a nonlinear three-dimensional seismic isolationsystem called vertical rocking isolation (VRI) system, based on devices called ISO3D. Unlikeconventional seismic isolators, the ISO3D device is vertically flexible and laterally stiff. Although the proposedsystem can be applied to any type of structure, it is particularly attractive as a seismic protectionsystem of special structures, such as fluid storage tanks supported on legs, power transformers and sensitiveequipment with vertical acceleration. In this research an application to legged wine storage tanks ispresented. Two models were studied: a 3 m3 tank with 4 legs, and a 30 m3 tank with 6 legs. The fluidstructureinteraction was considered using a quasi-static approach, where the fluid behaves as a massattached to the tank walls. Time-history analyses results show average reductions of axial loads and shearloads on the legs of 57% and 61%, respectively. Finally, a fragility analysis indicates that the PGA requiredto reach 50% of probability of failure increases by an average of 153% by using the VRI system.