Electrorheological dampers and semi-active structural control
Electrorheological (ER) fluids have a number of properties that make them attractive for use in fluid-filled dampers. Our interest is in the use of such dampers for semi-active structural control. This paper provides an introduction to this subject, with emphasis given to control of large structural systems such as buildings and bridges when excited by ground motions of wind forces. It is assumed that multiple electrorheological dampers are embedded as a part of the structural system. A key aspect in the effective use of these electrorheological dampers for active control is the recognition that they are inherently nonlinear devices, the inputs being (essentially) the electric field levels applied to the electrorheological fluids in the dampers. A decentralized bang-bang control strategy is derived to minimize the rate at which energy from the disturbance is transferred to the structure. It requires feedback of the ER damper deformation rates and feedforward of a disturbance signal. The control strategy is simple to implement and has a number of desirable closed loop properties. A two degree of freedom example, illustrating base isolation of a simple building structure, is used to illustrate these closed loop properties.