Semiactive Tuned Mass Dampers

Studies have already demonstrated the successful use of linear semiactive damping devices, such as variable orifice (VO) dampers, for semiactive TMD systems. More recently, nonlinear semiactive damping devices, such as magnetorheological (MR) dampers, have also been shown to be effective for semiactive control of TMDs. Though semiactive dampers differ widely, with responses ranging from linear (VO) to nonlinear (MR), criteria for choosing an optimal semiacive device for a TMD have not been rigorously developed. This paper expands knowledge of semiactive TMD systems by assessing the effect of nonlinearity in the damping device on the effectiveness of a semiactive TMD. This is achieved by simulating a variable damping device (linear), and a variable friction device (nonlinear). The variable damping device consists of a VO damper, while the variable friction device consists of a new mechanically robust and reliable damping device with a dynamic resembling the MR damper. These simulations allow the influence of nonlinearity to be investigated and provide further insight into selecting an optimal semiactive damping device for improving the performance of a passive TMD. Introduction Recent decades have marked a trend towards the design and construction of very tall buildings. Advancements in analysis, coupled with an increased use of lighter building materials and a decrease in heavy claddings, have led to structures that are not only taller but also more flexible. Consequently, most modern towers are especially prone to oscillations under persistent winds, which can lead to swaying motions of several meters on the top floors (Chang, 1973, Miller, et al., 1988). In many cases, these large deflections may not threaten the integrity of the structure, but the steady rocking can cause considerable discomfort and even illness to building occupants. If persistent, the dynamic response under severe winds may render the top floors completely uninhabitable. Studies by Chang and Hansen investigated the effects of this motion on the human body, creating benchmarks for the perception of and physiological response to various increments of lateral acceleration (Chang, 1973, Hansen, et al., 1979). The maximum amplitudes of these responses are ultimately dictated by the ability of the structure to dissipate energy; the more significant the energy dissipation, the smaller the vibrations. All structures naturally release some energy through mechanisms such as internal stressing, rubbing, and plastic deformations. In large modern steel structures, however, the total damping may amount to as little as 1% of critical, making them very vulnerable to dynamic resonance effects (Housner, et al., 1997). As a result, additional measures are generally necessary to meet serviceability standards. Since eliminating the excitation source is impractical, this necessitates implementing a control scheme to enhance the effective damping of the structure. 5WCSCM-274