Browsing by Author "Zemp Rene"

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    Development of a long-stroke MR damper for a building with tuned masses
    (2016) Zemp Rene; De La Llera Martin Juan Carlos; Saldias Molina Hernaldo Enrique; Weber, Félix; Pontificia Universidad Católica de Chile. Escuela de Ingeniería; Pontificia Universidad Católica de Chile. National Research Center for Integrated Natural Disaster Management
    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.
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    Experimental analysis of large capacity MR dampers with short- and long-stroke
    (2014) Zemp Rene; De La Llera Martin Juan Carlos; Weber, Félix
    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.
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    Multiphysics behavior of a magneto-rheological damper and experimental validation
    (2014) Sternberg Cunchillos Alan Phillip; Zemp Rene; De La Llera Martin Juan Carlos; Pontificia Universidad Católica de Chile, National Research Center for Integrated Natural Disaster Management
    This investigation deals with the design, manufacturing, and testing of a large-capacity MR damper prototype. The MR damper uses external coils that magnetize the MR-fluid as it moves out of the main cylinder through an external cylindrical gap. In its design, multi-physics numerical simulations are used to better understand its force-velocity constitutive behavior, and its eventual use in conjunction with tuned mass dampers for vibration reduction of high-rise buildings. Multi-physics finite element models are used to investigate the coupled magnetic and fluid-dynamic behavior of these dampers and thus facilitate the proof-of-concept testing of several new designs. In these models, the magnetic field and the dynamic behavior of the fluid are represented through the well-known Maxwell and Navier-Stokes equations. Both fields are coupled through the viscosity of the magneto-rheological fluid used, which in turn depends on the magnetic field strength. Some parameters of the numerical model are adjusted using cyclic and hybrid testing results on a 15 ton MR damper with internal coils. Numerical and experimental results for the 15 ton MR damper showed very good agreement, which supports the use of the proposed cascade magnetic-fluid model. The construction of the 97 ton MR damper involved several technical challenges, such as the use of a bimetallic cylinder for the external coils to confine the magnetic field within a predefined magnetic circuit. As it should be expected, test results of the manufactured MR damper show that the damping force increases with the applied current intensity. However, a larger discrepancy between the predicted and measured force in the large damper is observed, which is studied and discussed further herein. (C) 2014 Elsevier Ltd. All rights reserved.
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    Tall building vibration control using a TM-MR damper assembly: Experimental results and implementation
    (WILEY, 2011) Zemp Rene; De La Llera Martin Juan Carlos; Almazan Campillay Jose Luis
    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. Copyright (C) 2010 John Wiley & Sons, Ltd.