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Performance Evaluation of Diaphragms in Tub Girder Superstructures

Dolati, Abouzar | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52152 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Maleki, Shervin
  7. Abstract:
  8. In recent years, steel tub girder superstructures have been exceedingly used in long span superstructures due to their significant torsional and flexural stiffnesses. In such superstructures, end diaphragms made of plates are one of the most important members in transferring seismic forces to the substructure. Despite the importance of end diaphragms, limited number of studies have been conducted on their behaviour and as a result, their design procedure is not clear. In this dissertation, different configurations of end diaphragms in elastic steel tub girder superstructures were evaluated using finite element models and the required equations for stiffness and strength were derived. Moreover, using the results obtained, design guides were provided. In addition to the performance of end diaphragms in elastic superstructures, its behavior in inelastic superstructures were evaluated. Some charactristics of the end diaphragm plate such as high elastic stiffness, dominant shear behavior and considerable energy absorption capability, make them suitable as ductile elements in reducing seismic demands. Therefore, internal and external ductile diaphragms were suggested by some modifications in existing plate diaphragms of tub girder superstructures. In both cases, parametric study models were employed to evaluate the different superstructures, including ductile diaphragms, under nonlinear quasi-static loading. Results showed that the seismic demands transferred to the substructure were reduced significantly by using the proposed ductile diaphragms. In addition to the finite element analyses, analythical equations were derived and response modification factors were calculated. Moreover, nonlinear time history analyses were employed to prove the adequate ductile behavior of the selected models under real moderate and strong ground motions
  9. Keywords:
  10. Internal Diaphragm ; Tub Girder Bridges ; External Diaphragm ; Ductile Diaphragm ; Seismic Assessment ; Support Diaphragm

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