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SUMMARYThis investigation deals with the torsional balance of the earthquake response and design of elastic asymmetric structures with frictional dampers. Plan asymmetry leads to an uneven lateral deformation demand among structural members and to unbalanced designs with larger capacities in some resisting planes. Frictional dampers are capable of controlling lateral-torsional coupling by placing the so-called empirical center of balance (ECB) of the structure at equal distance from all edges of the building. This rule is developed for single-story systems with linear and inelastic behavior. However, recently obtained theoretical and experimental results demonstrate that this rule carries over to multistory structures. Results show that the peak displacement demand at the building edges and that of resisting planes equidistant from the geometric center may be similar if the damper is optimally placed. It is also shown that torsional ampliÿcation of the edge displacements of arbitrary asymmetric structures relative to the displacement of the symmetric counterparts are approximately bound by a factor of 2. Furthermore, frictional dampers are equally e ective in controlling lateral-torsional coupling of torsionally exible as well as sti structures.

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...

SUMMARYDifferent modelling aspects of structures isolated using the frictional pendulum system and subjected to earthquake ground motions are studied herein. Although the vertical dynamics of these structures is given special emphasis, other effects such as large isolator deformations and bidirectional input motion are also considered. Different structural models of the FPS are developed and tested for single-storey structures and a real four-storey building frame; among them, an 'exact' formulation of the FPS force-deformation constitutive relationship is presented. Results show that global building responses can be computed within 20 per cent error in the mean using a simplified model that ignores the vertical motion of the building; however, structural member deformations and forces need to be computed using a model that considers such motion. This is of particular importance when there exist correlation between the horizontal and vertical components of ground motion. Further, a physical model of the FPS is introduced and used to determine the response of a real four-storey frame, including uplift and downward impact. Results from this analysis show that local column responses may vary substantially depending on the stiffness of the isolation storey and the presence of a mass at the isolation level. Such mass is capable of filtering the large increase in column shear that results from the impact of the structure after uplift. Uplift occurs at several instants of the response of the structure considered, leading to an increase in column base shear as large as 3 times the shear obtained by ignoring the vertical dynamics of the building.1998 John Wiley & Sons, Ltd.