Controlling structural vibrations via smart variable dampers: experimental investigations and possible applications

Special dampers for structural control of earthquake induced vibrations are considered herein. The silicone oil of conventional viscous dampers is replaced by a magnetorheological (MR) fluid, which is able to change, by orders of magnitude, its viscosity according to the magnetic field in which it is immersed in. MR dampers probably represent the easiest way to materialize the concept of smart devices for semi-active (SA) structural control: their mechanical properties can be adjusted almost instantaneously according to the seismic input characteristics or to the instantaneous structural response. Two experimental activities are presented: the first one characterizes the electric and mechanical behavior of two prototype MR dampers manufactured in Germany; the second one consists of shaking table tests on a large scale steel structure equipped with MR devices, showing the effectiveness of the SA control strategy. Interactions between MR based structural control and seismic early warning systems (SEWS) are investigated, with reference to a case study (highway bridge in California). The idea consists in changing the MR damper behaviour according to the forecasted intensity of an incoming earthquake provided by the SEWS, in order to obtain the optimal seismic response of the structure. Finally, a possible integration of SA control and structural monitoring systems is envisioned, starting from the analysis of all the aspects and practical issues involved in both the technologies and highlighting the advantage in sharing them for practical applications.