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Earthquake Engineering and Engineering Vibration
Theoretical and practical issues concerning the multi-faceted task of mitigating the latero-torsional seismic response of a prototypal frame structure with asymmetric mass distribution are approached. Chevron braces with embedded magnetorheological dampers acting on the interstory drift are used to ensure additional energy dissipation. The semi-active control strategy employed to govern the modification of the damper characteristics via feedback is based on the selection of optimal forces according to a H2/LQG criterion, with respect to which the actual forces are regulated by a clipped-optimal logic. A dynamic observer is used to estimate the state through a non-collocated placement of the acceleration sensors. Several aspects to be addressed throughout the complex process including the design, modelization, and implementation phases of semi-active protection systems are discussed. Finally, experimental results obtained to mitigate the motion induced by ground excitation in a large-scale laboratory prototype, simulating the seismic response of a two-story building, are summarized.
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IGI Global eBooks
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A solution for avoiding the harming effects of strong earthquakes or strong winds is the Structural Control [Yao 1972]. The author started a research envisioning to control the response of large structures with many active devices. The analytical study is succeeded to show that optimal active control can be used. An energy-based method of generating the parameters of control was developed. Using optimal active control method, it is possible to control large structures using many devices and, this way, the efficiency and reliability of the control are highly increased. The paper presents results obtained when large structures (as long bridges and tall buildings) equipped with several active tuned mass dampers acting on different levels and directions are subjected to strong time-history seismic acceleration records. It is shown that the response is considerably reduced. At the same time, the characteristics and the performances of the actuators are presented. The results are also sho.
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Structural control systems are considered an effective alternative for reducing vibrations in civil structures and are classified according to their energy supply requirement: passive, semi-active, active and hybrid. Commonly used structural control systems in buildings are passive friction dampers, which add energy dissipation through damping mechanisms induced by sliding friction between their surfaces. Semi-Active Variable Friction Dampers (SAVFD) allow the optimum efficiency range of friction dampers to be enhanced by controlling the clamping force in real time. This paper describes the development and performance evaluation of a low-cost SAVFD for the reduction of vibrations of structures subject to earthquakes. The SAVFD and a benchmark structural control test structure were experimentally characterized and analytical models were developed and updated based on the dynamic characterization. Decentralized control algorithms were implemented and tested on a shaking table. Relative displacements and accelerations of the structure controlled with the SAVFD were 80% less than those of the uncontrolled structure
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Structures constructed in developing world are typically RC frames with masonry infill. These structures have little resistance for lateral loads caused by earthquake and wind. Even for adequately designed structures also, due to permissible deformation beyond elastic limits, failure of masonry causes severe loss of life and property. In the case of structures designed to sustain excessive deformation such as of defence establishments, functioning and serviceability of machines and equipment installed therein are adversely affected. This co-lateral damage may be reduced by adopting another design philosophy of structure response control. In this methodology, a supplementary damping device is incorporated in the primary structure, which absorbs most of the seismic energy imparted to it, restricting the structural response within serviceable limits. These devices may be passive, active, semi-active or hybrid types. Other than passive all options are technology-intensive and dependent on external energy source, not a favourable proposition for developing nations. Among all the passive devices, tuned liquid dampers (TLDs) promise to be most suitable. Here, existing overhead water tanks (OHWT) may be used as TLD with slight adjustment and modification. This method will be able to control the structural response without putting any extra load on the existing or newly-designed buildings. This paper reviews various types of dampers and discusses evolution of tuned liquid dampers. A method has also been proposed for incorporating TLDs in existing and new structures. This methodology may be very useful for structures of defence establishment which are scattered and remotely placed by location, housing important equipments sensitive to vibrations, as it is free from external power dependence and regular maintenance.
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CISM International Centre for Mechanical Sciences
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Computer-Aided Civil and Infrastructure Engineering
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Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015)
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Structural Control and Health Monitoring
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