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

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