Double variable frequency pendulum isolator for seismic isolation of liquid storage tanks

▶ The seismic response of liquid storage tanks isolated by the DVFPI is investigated. ▶ Four DVFPI design cases are considered by varying properties of the both surfaces. ▶ Criterion to optimize its performance is proposed based on minimum responses. ▶ Different stiffness of top and bottom surfaces optimizes the DVFPI for a slender tank. ▶ Equal stiffness of top and bottom surfaces optimizes the DVFPI for a broad tank.