Seismic soil-structure interaction for pile supported systems
Di Laora, Raffaele (2009) Seismic soil-structure interaction for pile supported systems. [Tesi di dottorato] (Inedito)
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Civil engineering structures involve structural elements with direct contact with ground. When the external actions, such as earthquakes, act on these systems, neither the structural displacements nor the ground displacements, are independent of each other. The process in which the response of the soil influences the motion of the structure and the motion of the structure influences the response of the soil is termed as soil-structure interaction (SSI). Damage occurred in recent earthquakes, have highlighted that the seismic behaviour of a structure is highly influenced not only by the response of the superstructure (considered as fixed based), but also by the response of the foundation and the ground as well. Hence, some modern seismic design codes impose that the effect of SSI must be taken into account, even if only in particular situations (depending on the particular Code). The complex 3-component interaction (soil-foundation-structure) may be analysed (in the hypothesis of linear elasticity) with reference to two separate interaction, reflecting distinct physic phenomena. The first one is the modification of the input motion at the base of the structure due to the different stiffness of the foundation with respect to the soil, referred to as kinematic interaction; the structure vibrates (because of its inertia) in dependence also of the soil-foundation system, and the latter experiences additional deformations (inertial interaction). The thesis deal with seismic SSI problems for pile supported structures with particular reference to the design aspects in the light of the recent Italian Codes and Eurocodes. In fact, despite the state of the art in SSI analyses has evolved steadily over the last decades, the state of practice for engineering characterization of SSI effects for routine structures has not undergone recent similar advancement. For this reason, aim of the thesis is: - to better understand the mathematical and physical meaning of kinematic interaction; - to provide simplified formulas for evaluating its effects in terms of bending moments (interface and pile head);to find simply rules to estimate the importance of “filtering effect” exerted by piles on foundation input motion; - to investigate the relative importance of kinematic vs. inertial interaction; - to provide a criterion to combine inertial and kinematic maximum effects.
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