This research investigates the seismic and harmonic response of a true free-plan tall building equipped with two tuned pendular inertial masses (TMs) and magnetorheological (MR) dampers. Construction of this proof-of-concept building was completed in 2007, and it is the first of its class in Chile. This article provides research results associated with this specific implementation; however, in order to make the results applicable to other building cases a parametric study was considered. A brief description of the structure and TM implementation together with the nonlinear equations of motion of the TM-MR damper assembly are presented. Building displacements and accelerations are computed and analyzed for a suite of subduction-type and near field ground motions. Besides, a new physical controller for the MR dampers is proposed and analyzed. The performance of this controller is compared with that of benchmark LQR controllers. In general, the TM-MR damper assembly improves the lateral performance of this structure for lateral harmonic excitations. However, the expected peak and RMS response modification factors and efficacy of the solution for earthquake excitations are strongly dependent on the frequency content of the excitation.damper to semiactively control a tuned mass, and the evaluation of the true performance of such solution for the free-plan building concept.It is well known that the efficacy of a TM depends on the frequency content of the excitation and the dynamic properties of the structure. There is general consensus that tuned masses are effective in reducing the response due to harmonic excitations [1] and wind excitations [2]. However, for seismic actions, there is no general agreement. For instance, some authors conclude that a TM combined with an optimal viscous damper is not effective in reducing the response due to earthquake excitations [3,4]. On the other hand, several analytical studies have shown that by connecting a TM to a semi-active MR device in structures subjected to earthquake and harmonic excitation, it is possible to improve the building performance [5][6][7][8][9]. In either case, questions such as the tuning frequency for a pendulum under large deformations, the optimal selection of damping in such case, and the effectiveness of a semiactive device versus a passive device, are not obvious decisions in this application.MR-dampers are semi-active MR fluid devices with a very low power requirement where a magnetic flux changes the fluid from a free-flowing linear viscous fluid state to a semi-solid state with controllable yield strength [10]. Due to this property, the reactive force applied on the TM by the MR-damper can be dynamically controlled within a range. The first full-scale application of an MR-damper was done in 2001, when two 30-ton MR-dampers were installed at the Tokyo National Museum of Emerging Science and Innovation. Additionally, different types of control strategies for a TM using MR-dampers have been investigated in the literature [6][7][8][9].This article invest...

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This paper summarizes the relevant results of the design, construction, testing, and implementation of a nominal 120 kN magnetorheological damper developed to control a free-plan tall building in Santiago, Chile, equipped with two 160-ton tuned masses. Cyclic as well as hybrid simulation tests were performed on the prototype damper. Global building responses using measured MR properties showed good correlation with analytical estimations. Also, a proposed physical controller for the MR damper was validated through hybrid and building pull-back tests. Its performance is essentially equivalent to that of an LQR controller, but the information needed in its implementation is considerably less. Pull-back tests of 10 cm amplitude were performed on one mass along the flexible edge of the building and its response controlled using the passive and controlled modes of the MR damper. The MR damper was capable of controlling the TM displacements very effectively, as well as the simulated building response for different ground motions and harmonic excitation.

The purpose of this article is to study and characterize experimentally two magneto-rheological dampers with short- and long-stroke, denoted hereafter as MRD-S and MRD-L. The latter was designed to improve the Earthquake performance of a 21-story reinforced concrete building equipped with two 160 ton tuned pendular masses. The MRD-L has a nominal force capacity of 300 kN and a stroke of ±1 m; the MRD-S has a nominal force capacity of 150 kN, and a stroke of ±0.1 m. The MRD-S was tested with two different magneto-rheological and one viscous fluid. Due to the presence of Eddy currents, both dampers show a time lag between current intensity and damper force as the magnetization on the damper changes in time. Experimental results from the MRD-L show a force drop-off behavior. A decrease in active-mode forces due to temperature increase is also analyzed for the MRD-S and the different fluids. Moreover, the observed increase in internal damper pressure due to energy dissipation is evaluated for the different fluids in both dampers. An analytical model to predict internal pressure increase in the damper is proposed that includes as a parameter the concentration of magnetic particles inside the fluid. Analytical dynamic pressure results are validated using the experimental tests. Finally, an extended Bingham fluid model, which considers compressibility of the fluid, is also proposed and validated using damper tests.

This article deals with the development of a long-stroke MR-damper aimed to control, by reacting on a tuned mass (TM), the earthquake performance of an existing 21-story office building located in Santiago, Chile. The ±1 m stroke MR-damper was designed using the nominal response of the building equipped with two 160 ton pendular masses tuned to the fundamental lateral vibration mode of the structure. An extended physical on-off controller, a special current driver, a new real-time structural displacement sensor, and an MR-damper force sensor were all developed for this application. The physical damper and control were experimentally validated using a suite of cyclic and seismic signals. The real-time displacement sensor developed was validated by first using a scaled down building prototype subjected to shaking table tests, and then a real-scale free vibration test on the sensor installed horizontally at the foundation level of a building. It is concluded that the proposed TM and MR-damper solution is technically feasible, and for an equivalent key performance index also defined herein, more economical than a solution based on passive viscous dampers.