Analysis and design of ER damper for seismic protection of structures

An electrotheological (ER) fluid damper suitable for vibration and seismic protection of civil structures has been designed, constructed, and tested. The damper consists of a main cylinder and a piston rod that pushes an ER fluid through a stationary annular duct. The behavior of the damper can be approximated with Hagen-Poiseille flow theory. Under the presence of electric field, the ER fluid exhibits a finite yield stress of the order of 1.8 kPa at 3 kV/mm and manifests some elastic behavior before yielding. An elastic-viscoplastic law is proposed that predicts satisfactorily the fluid behavior obtained from viscometric tests at different frequencies. The contribution from the elasticity of the fluid is insignificant to the global response of the damper at the flow rates of interest, and it is shown that the damper response can be satisfactorily predicted with a simple rigid-viscoplastic law. Experimental results on the damper response with and without the presence of electric field are presented. As the rate of deformation increases viscous stresses prevail over yield stresses and a smaller fraction of the total damper force can be controlled. Some design recommendations on ER dampers for seismic protection applications are provided.