Seismic control system for elevated liquid storage tanks using roll-n-cage isolator

Liquid containing elevated tanks are critical and strategic structures. Past earthquakes has shown that the damage occurs in form of buckling of tank wall due to development of excessive compressive stresses, failure of piping system and uplift of anchorage system. In such cases seismic base isolation plays a vital role in safeguarding the structure. Base isolation is one of the most widely accepted seismic protection systems used for the structures in earthquake prone areas. Base isolation may be done by introducing different types of bearings in the foundation & base soil. This can be achieved by providing rollers and /or spring in between foundation & base soil. In this paper, the response of the structure is obtained by modeling and analyzing the RCC elevated liquid storage tank in SAP2000. Two types of elevated liquid storage tanks mainly slender and broad tanks with capacities 350m³ and 500m³ respectively, isolated by the roll-n-cage bearing isolator are investigated under real earthquake ground motion. Two types of base condition for slender and broad tanks viz fixed base tank and base isolated tanks in which the bearing is placed at the base of the column at the foundation level are considered. Non-linear time history analysis for 1940 Imperial Valley (Elcentro) earthquake has been carried out for various conditions of tank viz tank full, tank 75% filled, tank 50% filled, tank 25% filled and tank empty. Parametric study has been carried out to study the response of tank with and without isolator. Various parameters like time period, base shear and displacement at top and bottom of the tank are studied.