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The Effect of Partial Foundation Uplift on Seismic Performance of Structures

Jafarieh, Amir Hossein | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47066 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ghannad, Mohammad Ali
  7. Abstract:
  8. It is well-known that the behavior of soil-structure systems can be well described using a limited number of non-dimensional parameters. This is the outcome of researches based on the premise that the foundation is bonded to the ground. Here, it is shown the concept can be extended to systems with foundation uplift. A set of non-dimensional parameters are introduced which controls the main features of uplifting systems. The super-structure is modeled as an equivalent single-degree of freedom system with elastic behavior mounted on a rigid foundation resting on distributed tensionless Winkler springs and dampers. The effect of foundation uplift on response of soil-structure systems are investigated parametrically through time history analysis for a wide range of systems subjected to ground motions recorded on different soil types. In particular, the effects of uplift on displacement ratio, defined as the ratio of maximum displacement of the uplifting system to that of the elastic system without uplifting and drift ratio, defined as the ratio of maximum drift of the structure as a part of uplifting soil-structure system to that of the elastic system without uplifting, are investigated. It is observed that although total displacement of systems increases because of foundation uplift but in general foundation uplift reduces the drift response of structures, which in turn, results in lower base shear. Also, the simultaneous effects of soil-structure interaction, foundation uplift and inelastic behavior of the super-structure on total displacement response of soil-structure systems are investigated. The super-structure is modeled as an equivalent single-degree of freedom system with bilinear behavior. It is shown that while uplifting soil-structure systems experience excessive displacements, in comparison with systems which are not allowed to uplift, ductility demand in the super-structure generally decreases due to foundation uplift. In the next step the inelastic behavior of soil was included in the models. It was shown that although the total displacement of soil-structure systems allowed to uplift increases because of nonlinear soil behavior but the ductility demand of the structure as a part of soilstructure system decreases more in comparison with the systems that are allowed to uplift on elastic soil. Also the effect of foundation uplift was investigated on a number of frames. It was shown that the prediction of single degree of freedom models about the influence of foundation uplift on the response of soil-structure systems is applicable for multi degree of freedom systems. Finally, the results of new inelastic displacement ratio for uplifting soil-structure systems were compared with the coefficient provided by traditional seismic provisions. It was shown that using the new inelastic displacement ratio in nonlinear static procedure can improve the ability of the procedure to predict the response of soil-structure systems allowed to uplift
  9. Keywords:
  10. Soil-Structure Interaction ; Foundation Uplift ; Inelastic Displacement Factor ; Seismic Performance ; Ductility Demand ; Drift Ratio ; Inelastic Soil Behavior

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