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Optimal Design of Passive Control Systems Using Siffness Reduction and Viscous Damping Devices Using Instantaneous Optimal Control and Polynomial Control Algorithms

Sahami, Kaveh | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45236 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadizadeh, Mehdi
  7. Abstract:
  8. In this study, an active control strategy is used for design of passive energy dissipation systems using viscous fluid dampers and structural stiffness modification. The combination of supplemental damping and modification (usually reduction) of stiffness is used to minimize the two main structural response parameters, namely the maximum inter-story drifts and maximum absolute accelerations. In this manner, both structural and nonstructural damages can be controlled.
    While active control systems are expected to improve the structural esponse beyond what can be achieved in passive control, the practical implementation of control systems are mostly of passive type. This is mainly due to high construction and maintenance costs associated with active control systems. For this reason, by using an active control algorithm in design of passive systems, it is attempted to obtain a structural response as close as possible to what can be obtained using active control.The proposed design procedure consists of two major steps. In the first step, the structure is softened by reduction of stiffness. This can be carried out to result in suitable natural frequencies for the structure considering the excitation properties, or merely considering the conditions of the structure. This usually increases the displacement response, but also reduces the acceleration response, thus helping the control system to keep the acceleration response limited. Then using one of the instantaneous optimal control or polynomial control algorithms, an active control system is designed to minimize a weighted combination of maximum inter-story drift and maximum absolute acceleration response, known as a structural performance index. Here, the active control algorithm is slightly modified, so that the resulting properties can be achieved using merely passive control devices. It is also attempted to limit the required changes in the stiffness other than the initial stiffness reduction, so that the stiffness modification requirements remain practical. In the second step, the properties of the passive dampers are selected such that a response close to that of the active control system is obtained.Case studies have been carried out to demonstrate the design technique and it is application. It is shown that the resulting passive control system performs equally well, or better than the ordinarily-designed optimal passive control system. However, some performance degradation compared to the equivalent active control system is usually observed, that is mainly attributed to the flexibility of the braces used to connect the dampers to the structure
  9. Keywords:
  10. Passive Control ; Active Control ; Supplemental Damping ; Instantaneous Optimal Control Algorithm ; Polynomial Control ; Softening Damping ; Viscous Damper

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