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Experimental and Numerical Investigation of Laminated Elastomeric Bearings Used as Seismic Base Isolator Considering Long Term Loading Effects

Maghsoudi Barmi, Ali | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53230 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khaloo, Alireza
  7. Abstract:
  8. Eliminating the tensile stresses and providing a cost-effective isolation system, has made the unbounded isolators an attractive option. Following this idea and the results obtained by various researchers, it is shown that unbounded steel-reinforced elastomeric bearings (SREBs), which are used and designed for service limit state, have inherently acceptable characteristics for a cost-effective isolation system and can provide improved structural performance. However, this inherent capacity is neglected in the design process.The current research presents an experimental program to analyze the mechanical properties of steel-reinforced natural rubber bearings without the upper and lower endplates when subjected to large shear displacements and to measure how this inherent capacity can be used considering long-term loading effects. The overall behavior of the bearing is explained and the affecting variables including the level of axial load, rate of loading, and contact conditions are discussed. Moreover, the life-time performance of the bearings was investigated in three phases; (1) effects of long-term service, namely the long term presence of vertical loading at service limit state, on the mechanical properties of the bearings, (2) effects of consecutive shear loading at different amplitude in presence of permanent loading, and (3) post-earthquake behaviour of the bearing against service load conditions. An innovative test setup was utilized in which the initial situation of the bearings remains unchanged, i.e., bearings do not experience unloading. Using this setup, a realistic loading condition is provided and the contact surface conditions also remain unchanged. It was shown that vertical stiffness, shear stiffness, and damping coefficient of the bearing which are the main parameters of an isolation system, might experience some changes during the life-time of the bearing. However, based on the results obtained, the life-time performance of the SREBs as an isolation system in bridges was evaluated as satisfactory and a durable performance was observed for this type of bearings.Furthermore, in the second phase of this research seismic performance of bridge equipped with this isolation system is investigated using analytical models and fragility curves for this bridge was developed. Effects of parameters like bounding, friction coefficient, and aging of the bearing are investigated and corresponding fragility curves are calculated and compared with each other. The software SAP2000 is used for modelling and the nonlinearity of the elements is considered in the modelling process. The results obtained in this part, showed a satisfying performance for these bearings while used as an isolation system
  9. Keywords:
  10. Elastomeric Bearings ; Fragility Curve ; Bridges ; Base Isolation ; Seismic Isolation ; Long Term Loading ; Seismic Isolator ; Boundedness

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