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Control of civil engineering structures for earthquake hazard mitigation represents a relatively new area of research that is growing rapidly. Control systems for these structures have unique requirements and constraints. For example, during a severe seismic event, the external power to a structure may be severed, rendering control schemes relying on large external power supplies ineffective. Magnetorheological (MR) dampers are a new class of devices that mesh well with the requirements and constraints of seismic applications, including having very low power requirements. This paper proposes a clipped-optimal control strategy based on acceleration feedback for controlling MR dampers to reduce structural responses due to seismic loads. A numerical example, employing a newly developed model that accurately portrays the salient characteristics of the MR dampers, is presented to illustrate the effectiveness of the approach.

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The magnetorheological (MR) damper is one of the most promising new devices for structural vibration reduction. Because of its mechanical simplicity, high dynamic range, low power requirements, large force capacity and robustness, this device has been shown to mesh well with application demands and constraints to offer an attractive means of protecting civil infrastructure systems against severe earthquake and wind loading. In this paper, an overview of the essential features and advantages of MR materials and devices is given. This is followed by the derivation of a quasi-static axisymmetric model of MR dampers, which is then compared with both a simple parallel-plate model and experimental results. While useful for device design, it is found that these models are not sufficient to describe the dynamic behavior of MR dampers. Dynamic response time is an important characteristic for determining the performance of MR dampers in practical civil engineering applications. This paper also discusses issues affecting the dynamic performance of MR dampers, and a mechanical model based on the Bouc-Wen hysteresis model is developed. Approaches and algorithms to optimize the dynamic response are investigated, and experimental verification is provided.

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In this paper, the efficacy of magnetorheological (MR) dampers for seismic response reduction is examined. To investigate the performance of the MR damper, a series of experiments was conducted in which the MR damper is used in conjunction with a recently developed clipped-optimal control strategy to control a three story test structure subjected to a one-dimensional ground excitation. The ability of the MR damper to reduce both peak responses, in a series of earthquake tests, and rms responses, in a series of broadband excitation tests is shown. Additionally, because semi-active control systems are nonlinear, a variety of disturbance amplitudes are considered to investigate the performance of this control sytstems over a variety of loading conditions. For each case, the results for three clipped-optimal control designs are presented and compared to the performance of two passive systems. The results indicate that the MR damper is quite effective for structural response reduction over a wide class of seismic excitations.

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