Seismic Protection of Structures with Supplemental Rotational Inertia

Abstract

This paper investigates the alternative strategy of suppressing ground-induced vibrations with supplemental rotational inertia. The proposed concept employs a rack-pinion-flywheel system where its resisting force is proportional to the relative acceleration between the vibrating mass and the support of the flywheels. This arrangement, known in the mechanical networks literature as the inerter, complements the traditional supplemental damping and stiffness strategies used for the seismic protection of structures. The paper shows that the seismic protection of structures with supplemental rotational inertia has some unique advantages, particularly in suppressing the spectral displacements of long period structures—a function that is not efficiently achieved with large values of supplemental damping. The paper shows that this happens at the expense of transferring appreciable forces at the support of the flywheels and proceeds by examining to what extent the finite stiffness and damping of the support of the flywheels affects the dynamics of the system. The proposed concept may be attractive for the seismic protection of bridges given that the rack-pinion-flywheel system strategy can accommodate large displacements.