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Evaluation of Seismic Criteria and Random Parameters on Fragility Curves of RC Frames

Asadi, Payam | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44423 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Bakhshi, Ali
  7. Abstract:
  8. There are many parameters which are utilized to obtain a more reasonable performance for structures under earthquake excitations in seismic provisions. It is well recognized that the main character to design of structures under seismic excitation is probabilistic rather than deterministic; therefore, it should be determined if the probability of structural damages is decreased when such parameters change in design of structures. In this thesis, fragility curves are developed in order to evaluate these parameters. Fragility curves are employed for various probability parameters. These diagrams are utilized to demonstrate when a coefficient or a number of parameters are used to improve performance level of a structure. Moreover, it guarantees that the probability of damage limit states exceedance decreases, as it is expected. These diagrams can further illustrate the effect of uncertainty of design parameters. General considered parameters in seismic provisions are PGA, importance factor (I) and typical inherent overstrength and global ductility capacity (R). The results of evaluating these parameters reveal that by increasing global ductility capacity (R), the probability of damage exceedance is decreased; however, an increase in importance factor (I) for hospital buildings versus office buildings, cannot guarantee a decrease in the probability of damage exceedance. The PGA randomness results reveal that considering the PGA uncertainty does not mean that the probability of damage exceedance will be increased in general cases. Furthermore, a frame work is utilized to select and to verify prevalent seismic design codes. For that, the damage quantity of the RC frames is compared with the target performance. Moreover, to achieve more efficient seismic codes, the level of these damages is compared. Due to the randomness property of designed structure and seismic excitations, this probabilistic problem should be evaluated. Fragility curve is developed in order to survey this problem. These diagrams further illustrate the effect of load combinations and reduction factors of codes on probability of damage exceedance. Two types of structures are presented: high importancestructures with high ductility and medium important structures with intermediate ductility are designed by different seismic codes. The results reveal that usually lower damage ratio generates lower probability of extremeness. However, the findings indicate that there are buildings with higher bar masses which have higher probability of damage exceedance. Life-cycle cost analysis employed for efficient comparison and final decision-making process. This is a useful tool in economic analysis which exploits damage ratios and fragility curves simultaneously to assist the final decision and to select the proper code. Structural behavior of structures under earthquake excitations depends on many parameters. From offspring of these parameters, they divided into two main groups. The First group is the parameters depended on seismic parameters of the structure location, like earthquake hazard and seismic soil parameters. The second group is the structural property of elements. Performance of buildings calculated by comparison these damage indices with performance damage levels. Advanced procedure to evaluate structures used IDA and fragility curves. FEMA695 introduced an advanced procedure to evaluate seismic designed buildings. In this thesis by compound fragility curves and FEMA695 procedure a new procedure is introduced to evaluate structures. Effect of hysteresis behavior of seismic designed special ductility RC frames on fragility curves is evaluated by this procedure. However RC buildings designed by special ductility details have high strength and special details, but results displayed they are not sufficient. High pinching degradation in some hysteresis behavior increased damage indices. Both the damage indices and probability of damage exceedance are decreased allowable collapse margin ratio by prevention of pinching effect. Evaluation randomness properties of RC elements (f'c, E, fy) displayed that variations of these parameters in the fragility curves of designed buildings have affected slightly.
  9. Keywords:
  10. Fragility Curve ; Reinforced Concrete Frame ; Performance Based Design ; Seismic Design Codes

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