In this paper, we propose a design method to control the displacement of base-isolation layer using an oil damper that can change its damping coefficient relative to the displacement. The present damper provides large damping to reduce the response displacement of the base-isolation layer in severe or extreme seismic events, whereas it provides small damping to reduce the response acceleration of the superstructure in moderate seismic events.
A numerical optimization method, sequential quadratic programming, is employed to obtain an optimum set of parameters for the present damper. Design examples show that the base-isolation system with the optimally designed variable oil damper can satisfy the design criteria that cannot be satisfied with a system incorporating a conventional oil damper.
