A Comparative Study of the Performance of Bonded and Unbonded Elastomeric Isolators in Seismic Isolation of Above Ground Liquid Storage Tanks

One of the most common types of seismic isolators is steel reinforced elastomeric isolators (SREIs) which consist of alternating layers of elastomer and steel reinforcing plates. Unbonded fiber-reinforced elastomeric isolators (UFREI) represent a relatively new type of elastomeric isolators. In this type of isolator, to control lateral strain and provide vertical stiffness, FRP layers are used instead of steel plates. Additionally, to reduce the cost of isolators, the idea of removing the top and bottom connection plates and the unbonded use of isolators has been considered. In UFREIs, due to the rollover deformation and the reduction of the isolator horizontal stiffness, it is expected that the seismic isolation efficiency increases as compared to the bonded isolators. In this research, the performances of UFREIs and conventional SREIs in improving the seismic behavior of liquid storage tanks were evaluated and compared. The isolated water tank was modeled using a mass and spring model of three degrees of freedom with convective mass, impulsive mass, and rigid mass. Time history analyses were performed on the fixed-base storage tank as the benchmark structure and the two base-isolated tanks with steel-reinforced and unbonded fiber-reinforced isolators. The results show that both types of isolators are effective in significantly reducing the demand base shear in the tanks. However, seismic isolation increases the displacement demand in the convective mass. Regarding the comparison of the two types of isolators, it was observed that on average, UFREIs in slender and broad tanks are 33.5% and 23.9%, respectively, more efficient than the SREIs in reducing the maximum base shear forces. Also, there is no significant difference in the maximum displacement of the convective mass in the two isolation systems. The displacement and shear forces developed in the unbonded isolators were found less sensitive to the variations of the Peak Ground Acceleration (PGA) as compared with the conventional bonded isolators.