Seismic Isolation of Bridges with Double Variable Frequency Pendulum Isolator

The paper describes behaviour of multi-span continuous deck bridge isolated by the double variable frequency pendulum isolator (DVFPI). The governing equations of motion of the bridge-isolation system subjected to bilateral ground excitation are derived and solved in the incremental form. In order to investigate the behaviour of the DVFPI, the response is obtained under different parametric variations for a set of nine far-fault earthquake ground motions with low, medium and high intensities. Four different combinations of the DVFPI design cases having different isolator geometry and coefficient friction at top and bottom sliding surfaces are studied and the criterion to optimize its performance is proposed based on minimum responses and energy quantities. It is found that the performance of the DVFPI can be optimized by designing the top sliding surface with high initial stiffness relative to the bottom one and the coefficient of friction of both sliding surfaces to be equal.