## 3 Magnetorheological Dampers for Structural Buildings
### Application of MR Dampers in Building Structures  
Due to their superior quality, MR dampers are in high demand for use in scientific case studies and in several real-world industrial applications. [PERSON] and [PERSON] concluded that MR dampers provide good operating reliability as temperature fluctuations and impurities in the fluid did not affect the performance and functionality. However, a significant drawback was their nonlinear characteristics, which involve hysteresis (force vs. velocity and force vs. displacement). This makes accurately modeling MR dampers and developing an efficient algorithm for improved performance a challenge [142; 143]. Over the past 15 years, MR dampers have been widely used in a variety of fields for vibration control. These include [144; 145; 146; 147], but are not limited to, building structures [148; 149; 150; 151], bridges [149; 150], suspension systems in automotive and high-speed trains [152; 153; 154], advanced artificial limb systems [155], large washing machines [156], landing gears for airplanes [157; 158], commercial vehicle seats [159], complex mechanical systems [160], and rotor systems of helicopters [161]. However, despite their many advantages, MR dampers are difficult to commercialize due to their complex structures and user-dependent configurations [162; 136]. [PERSON] and [PERSON] (2010) discussed the use of semi-active structural control techniques within the framework of a civil engineering experimental model equipped with MR dampers. The study aimed to develop a semi-active damping device in the Comparison of Vibration Control in Civil Engineering Using Passive and Active Dampers (COVICO-CEPAD) project in the Eurocores S3T program framework. An experimental frame was set up at the Faculty of Engineering of the University of Porto (FEUP) to explore the calibration of MR dampers as well as identify the dynamic properties of small-scale metal frames with and without the use of specific MR devices (Figure 3). Some of the results from the simulation of the controlled frame under earthquake conditions were compared with the experimental results from a frame installed on a Quanser(r) Shake Table II [163; 164]. Data and characteristics that had been obtained from several earthquakes were used in the study to evaluate the performance of structures fitted with semi-active controllers. This information was fed into and calibrated by a Quanser(r) Shake Table II to experimentally and numerically compare the various control strategies. However, the study only yielded results when certain earthquake inputs, such as the El Centro earthquake, were used. In the numerical example, a three-storey structure was controlled using a MR damper on the first floor. The simulation showed that a clipped optimal control algorithm produced improvements in uncontrolled systems [163; 164]. Another study investigated the performance of two variations of passive and semi-active damping devices in a 12-story bearing frame (Figure 4). A segmented and insulated floor constituted the upper floor. The passive and semi-active devices were installed to reduce the seismic response of the structure [165]. Figure 4: Segmentation of the 12-story building: (**a**) Sketch of the 12-story building structure with ‘10 + 2’ and ‘8 + 4’ models; (**b**) Schematic of isolated sections [165]. Figure 3: Building structure with a metal frame and an installation [163]. The study used a semi-active control approach. To manipulate reaction forces, feedback controls that reset the system according to structural responses were applied to the device. A simplified two degrees of freedom system was adopted as the control parameter of the semi-active damping device. Response reduction factors of various seismic intensities were analyzed using time history analysis. The study found that the semi-active damping device effectively reduced the movement of the structure under a given seismic load in comparison with the passive system.