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Estimating the Seismic Reliability of the Structures Based on Modal Nonlinear Probabilistic Analysis

Zarfam, Panam | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 41294 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Mofid, Massoud
  7. Abstract:
  8. Concerning the variety of existing buildings and the diversity in the factors which affect the behaviors of structures, subjected to earthquakes, presenting a definite method for studying their seismic vulnerabilities has not been realized yet. Selecting a method which covers all mentioned necessities is extremely wide and complex. From one side, the capacity of structural system should be determined based on its strength and deformability. On the other hand, the nonlinear behavior of structure should be predicted by selecting the probable effects of earthquake on the region. Then, the force or acceleration which causes damage of structure's components, and the whole structural system, should be calculated based on the obtained results. Nonlinear static analysis is among the tools used in such methods. This method can easily simulate the nonlinear behavior of structure and present appropriate approximation of nonlinear dynamic analysis by using a lateral load pattern. In this regard, the accuracy and exactness of Modal Incremental Nonlinear Static Analysis have been studied on several steel bending frames with semi-rigid connections. Probability issue has entered the earthquake engineering due to the limited information of seismic parameters such as distance from seismic focus, frequency content, maximum ground acceleration and the uncertainties in contrast with ordinary analytical methods. In this research, an analytical basis is provided by applying two kinds of probabilistic distribution, and modeling uncertainties because of statistical nature of structural parameters. In this regard the efficiency level and considered probable reliability of structure is determined and a specific degree of certainty is guaranteed for the structure through which the realization level of its performance objectives is achieved. As the nature of probabilistic method is based on nonlinear dynamic analysis, it has been highly attempted to insert this new designing method into the existing guidelines based on the probability. However, as the deficiency of this method is its prolonged calculations regarding several degree of freedom structures, and the steps of obtaining results, the methods existing in the guidelines are still used for ordinary structures. For this purpose, a new analytical method, Modal Incremental Dynamic Analysis (MIDA), and using bilinear and tri-linear innovative ideas are presented for approximating the capacity curves of structures. This is an applicable method for studying seismic behavior of structures and their actual performances under earthquake load. This method has feasible application, elevated computational speed and less tedious calculations, as well as reliable accuracy in its outcomes.In the following, two probabilistic methods for seismic assessment of structures, seismic reliability and the fragility of structures in different earthquake intensities as well as different methods of plotting fragility curves are studied concerning several cases of reinforced concrete bending frames. In all these methods it has been attempted to model numerically all existing random and known uncertainties as much as possible. In both mentioned methods, the structure's analytical data have been obtained based on Modal Incremental Dynamic Analysis (MIDA). Finally, a damage index caused by two- dimensional analysis has been studied which reflects the tridimensional behavior and distortion of structure
  9. Keywords:
  10. Modal Pushover ; Damage ; Reliability ; Incremental Dynamic Analysis ; Capacity ; Uncertainty ; Fragility Curve

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