On the effectiveness of two isolation systems for the seismic protection of elevated tanks

This paper deals with the effectiveness of two isolation systems for the seismic protection of elevated steel storage tanks. In particular the performance of High Damping Rubber Bearings (HDRB) and Friction Pendulum isolators (FPS) has been analyzed. As case study, an emblematic example of elevated tanks collapsed during the Koaceli Earthquake in 1999 at Habas Pharmaceutics plant in Turkey is considered. A time-history analysis conducted using lumped mass models demonstrates the high demand in terms of base shear required to the support columns and their inevitable collapse due to the insufficient shear strength. A proper design of HDRB and FPS isolator according to the EN1998 and a complete non-linear analysis of the isolated tanks proved the high effectiveness of both isolation systems in reducing the response of the case tank. Actually, the stability conditions imposed by the code and a reduced level of convective base shear obtained with the second isolation typology suggests the use of FPS isolators rather than HDRB devices