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Design of Passive Control Systems for Nonlinear Structures Using Active Control Algorithms and Modification of Structural Stiffness, Strength and Damping

Zare, Alireza | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51843 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadizadeh, Mehdi; Rofoei, Fayaz Rahimzadeh
  7. Abstract:
  8. The subject of this research is design of passive control systems for nonlinear structures using active control algorithms and modification of structural stiffness, strength and damping. All the systems considered are the categorized as the shear-type buildings. Furthermore, pole assignment and sliding mode algorithms are used as the proposed algorithms. The method used here to reduce the response of the system (the word “response” is referred to the absolute acceleration and inter-story of stories) to the optimum or desired values, implements the stiffness and strength reduction and increasing the damping. Reduction of stiffness and strength are used to prevent damaging non-structural and acceleration sensitive equipment. On the other hand, due to reduction of the stiffness and strength of the system or due to the direct need of reduction of inter-story drifts for reducing structural failures, the supplemental damping is used. In this method, at first the control forces of the stories in the modified active control system are determined in such way that the absolute acceleration and inter-story drifts meet the design criteria. Then, the active control algorithm is modified in such way that the extracted dynamic characteristics of the equivalent passive control system result the same behavior in the passive control system. Before proposing the method achieving above-mentioned goals, all the effective parameters in response of the passive control system is investigated using a sensitivity analysis. In this regard, reduction of stiffness and strength, increasing of structural damping and effect of stiffness of the braces connecting the dampers to the main system are considered in the sensitivity analysis of SDF and MDF systems. Between all effective parameters, adding supplemental damping and involving stiffness of bracing in analysis resulted different information in responses of the structure. For an example, unlike the linear systems, in nonlinear systems, fewer value of stiffness for the bracing is needed ignoring bracing stiffness in analysis. For a nonlinear SDF system excited by Northridge earthquake, a bracing stiffness about 3 times greater than the linear stiffness of the system is needed for losing about 5 percentage of the responses compare to the system with rigid bracing. This ratio is calculated about 5 for the linear system.Before implementing the mentioned method in pole assignment algorithm, the movement of the poles in the nonlinear systems is investigated. Then, the design procedure for the nonlinear control system with the selected poles using equivalent SDF is presented. Extending the implemented method in replacing nonlinear MDF systems with the equivalent SDF system in the controlled systems is one of the topics of this research. In a numerical example in a 6 story building using the proposed method, the reduction of about 63% is occurred compared with the uncontrolled system. Reduction of 37.8% resulted in maximum total acceleration in two mentioned structures.In the related section of the sliding mode algorithm, the modification needed of the algorithm is presented. The algorithm is modified in such way that an appropriate gain matrix for design of passive control system could be attainable. This goal is achieved by changing the active control forces. In a numerical example in an 8 story building using the proposed method, the reduction of about 79.3% is occurred compared with the uncontrolled system. Reduction of 15.8% resulted in maximum total acceleration in two mentioned structures
  9. Keywords:
  10. Active Control ; Passive Control ; Strength Reduction Factor ; Dampers ; Poles Assignment Algorithm ; Stiffness Reduction ; Sliding Mode Control

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