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Probabilistic Optimization of Structures Equipped with Active Vibration Control Systems Under Probable Mainshock-Aftershock Sequences
Khansefid, Ali | 2018
630
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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 51195 (09)
- University: Sharif University of Technology
- Department: Civil Engineering
- Advisor(s): Bakhshi, Ali; Ansari, Anoushiravan
- Abstract:
- Nowadays, the usage of probabilistic and reliability based frameworks is growing fast with respect to the development of computers. One of the most important issues which can be dealt in the field of structural/earthqauke engineering is the performance evaluation of the buildings equipped with active vibration control systems. In this research, in order to evaluate the performance of buildings probabilistically, the sampling simulation methods are applied. Accordingly, both structures and the loadings during their lifetime are considered as random variables. Therefore, at beginning, it is necessary to propose a model which is capable of producing structures with random properties. In this regard, three major parameters including number of stories, story stiffness, and story yielding force are considered as design parameters which are going to be generated randomly. Next, it is needed to procreate a model for generating random earthquake scenarios. Since, the main objective is to evaluate the buildings performances in their life span, a model is proposed for generating the random earthquake scenario (including magnitude, site to source distance, and occurrence time of mainshocks and aftershocks) based on the catalog of Iranian plateau. However, it is not enough, and another model is proposed to generate synthetic stochastic accelerograms for any random event generated by the previous model. This model is developed by using the accelerogram database of Iranian plateau, and is capable of distinguishing between mainshocks and aftershocks, as well as near-field and far-field records. In the next phase of the project, the performance of randomly generated buildings are evaluated under the random event scenarios during their lifetime. In addition, in another set of analysis, it is assumed that the buildings are equipped with active vibration control systems with LQR algorithm. These buildings are not retrofitted with the active vibration control systems, rather, they are designed initially with this system via optimization process. Unfortunately, there is no standard and code for design of active vibration control systems; therefore, herein, we use an advance two step optimization method. In the first step of this method, by using multi-objective optimization genetic algorithm, a set of non- prior optimal results are obtained. In the second step, a single objective life-cycle cost based optimization is performed. Among all non-prior optimal results of the previous optimization, the one with the minimum life-cycle cost (by considering cumulative damages during mainshocks and aftershocks) is selected as a final design. Finally, applying this method leads to obtain the optimal structural (story stiffness, and story yielding force) as well as active vibration control algorithm properties. Afterward, in accourdance to the Mont-Carlo simulation method, the above-mentioned procedure is repeated 5900 times to generate a reliable database of analysed building equipped with active vibration control system under random earthquake scenarios. Then, buildings behavior and damage costs are evaluated during ittheir lifetime and the efficacy of active vibration control system is assessed to improve the building lifetime behavior. In addition, the sensitivity analysis is performed to see which parameters (containing building and earthquake uncertainities) are more impulsive as a source of life-time damage costs of buildings with and without active vibration control system. Results show that the active vibration control system is well-capable of improving the structural performance under mainshock-aftershock sequenes, especially for more severe events. In addition, missing the aftreshocks leads to the considerable error in estimation of building damages during their life-time and consequently their life-cycle cost. Moreover, the pulse-like earthquake scenarios, cause slightly higher damage costs. Fianly, it is declared that it is not necessary to design the buildings and active control system simultaneously. Mechanical properties of buildings which were designed by the design code procedures were so closed to the ones obtained via concurrent design of building and active vibration control system
- Keywords:
- Probabilistic Optimization ; Multiobjective Optimization ; Structural Nonlinearity ; Active Vibration Suppression ; Accelerometery
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