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Developing Seismic Fragility Curves for Seismically Isolated Bridges

Bagheri, Hamed | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49396 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Bakhshi, Ali
  7. Abstract:
  8. Purpose of this research is to investigate the effects of different seismic isolation techniques and effect of their location on seismic behavior of assymetric bridges and on mitigating their seismic demand. According to different types of isolators and their possible locations, a research is necessary to help to choose the optimum choice among different possible choices for isolators and their location. In this strudy, Lead-Rubber Beraing (LRB), Friction Pendulum Systme (FPS) and High Damping Rubber (HDR) isolators have been investigated and 3D bridge models are 3-span concrete box girder with 50 meters long each span and each interior piers, 7 or 14 meters long. Isolators also can be located above or below piers. Considering differnet height for piers, different isolators, possible location for isolators and both isolated and fixed bridges, 42 models was produced. For assessing the effects of isolation, probabilistic methods and fragility curves have been employed in which material properties for concrete and steel as well as isolators, have been considered random variables and 100 ground motions representing seismic hazard uncertainty, have been exerted on the bridge models simultaneously in perpendicular directions. By doing Monte-Carlo sampling, 200 bridge-record samples for each of 42 models, comprising material and record uncertainty, was made. Then Non-Linear Time History Analysis has been performed on each of these samples. Results of these analyses have been used to draw component and system fragility curves. Finally, based on the derived fragility curves, it was found that seismic isolation has mitigated pier seismic demands drastically and among different isolators, LRB has the best performance. Moreover, by locating isolators below the piers, between foundation and piers, we can gain better performance and more decline will be seen in the seismic demand of piers in comparison with locating isolators above piers
  9. Keywords:
  10. Base Isolation ; Fragility Curve ; Monte Carlo Method ; Seismic Performance ; Asymmetric Bridge ; Monte Carlo Sampling

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