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An evaluation of stresses induced by centrifugal acceleration in a centrifuge test specimen

Dynamic centrifuge testing is a physical modeling technique widely used in evaluation of the response of geo-structures in seismic loading conditions. In the past few decades, numerous centrifuge experiments have been performed to assess the soil response under dynamic loading condition. These tests have provided invaluable insights into the key characteristics of soil dynamic properties and the potential failure mechanisms such as those caused by soil liquefaction. By subjecting a scaled model of a geo-structure to centrifugal acceleration, it is expected that the stresses within the scaled model become representative of those in the prototype geo-structure. The stresses induced by centrifugal acceleration are a function of the distance to the axis of rotation; therefore, the desired level of amplification of gravitational stresses is only achieved at a specific distance from the axis of rotation while the remaining part of the specimen are subjected to slightly smaller or larger levels of amplification. This non-uniformity of the gravitational field is often assumed to be small and is often ignored in numerical simulation of centrifuge experiments. The accuracy and consequence of this assumption has not been fully investigated. Here the effects of the variation of centrifugal acceleration within a centrifuge specimen are evaluated using a series of nonlinear finite element analyses. Moreover, to account for the relatively small radius of centrifuge arm in some centrifuge facilities, the flat ground surface in the prototype is often modeled using a curved surface in the centrifuge specimen. The effects of this geometric adjustment on the response of the centrifuge specimen are also discussed. Elastoplastic finite element simulations are used to shed light onto the relevance and efficiency of the experimental techniques used for preparing specimens that adequately represent a prototype. The numerical simulations, conducted by using classical as well as advanced elastoplastic constitutive models, reveal that the induced non-uniformities may lead to significant difference between the response of the centrifuge specimen and that of the prototype structure.

Author(s):

Mohamed El Ghoraiby    
George Washington University
United States

Majid Manzari    
George Washington University
United States