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Numerical Modeling of Rocking Of Shallow Foundations Subjected to Slow Cyclic Loading with Consideration of Soil-Structure Interaction

Fathi, Aria | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46784 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Foundation is the lowest load-bearing part of a structure and a part of underneath soil that is affected by the structure load. In fact, foundation transfers the loads from the superstructure to the substructure, preventing excessive settlement of soil or stresses exceeding soil bearing capacity. Indeed, almost all structures are placed on the ground, therefore the effects of soil and structure on each other, which is known as Soil Structure Interaction (SSI), is considered as a key factor in many important and engineered structures. In contrast to structures on a rigid footing, a flexible foundation may show stiffness degradation along with an increase of damping and natural period of the soil structure system. Strong vibration of the structures during earthquakes may result in an uplift or separation of a part of the shallow foundation from the underneath soil. Due to the non-linear and non-elastic behavior of the soil, any uplift may also affect the dynamic behavior of the structure. Rocking is one of the most important factors in describing the rotational behavior of a structure built on a shallow foundation. To study the effect of Rocking of shallow foundations subjected to slow cyclic loading with consideration of soil-structure interaction, a Finite Element Method (FEM) and ABAQUS software have been deployed to simulate the rocking motion of shallow foundations. For a more efficient simulation of the soil, both linear and non-linear elasto-plastic behavior of the soil has been taken into account in the analysis using the sub-routine coded in FORTRAN. Having many beneficial features during seismic loading, including probable increase in natural period of soil-structure system, the nonlinearity of the soil and rocking motion of shallow foundation may act as energy dissipation mechanisms, potentially reducing shaking demands exerted on the building. This nonlinearity, however, may result in permanent displacement of the soil which can damage the structures. The effectiveness of the rocking may enhance the performance of buildings during severe earthquakes. As a consequence, in this study, it has been suggested that rocking can be considered as a beneficial factor in engineered designs. However, civil engineers avoid non-elastic and non-linear behaviors in their designs which can be due to the uncertainties involved in the rocking mode during cyclic loads. In conclusion, with SSI and Rocking Effect consideration, the results indicate that allowing foundation to rock may result in stiffness degradation of the soil-structure system and also increasing energy dissipation at soil-structure interface, especially in high rise structures when subjected to cyclic loading
  9. Keywords:
  10. Foundation Uplift ; Energy Dissipation ; Soil-Structure Interaction ; Cyclic Loading ; Rocking Behavior

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