The Role of Transmitting Boundaries in Modeling Dynamic Soil-Structure Interaction Problems

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Author(s) Mohammed Y. Fattah | T. Schanz | Shatha H. Dawood
Pages 236-258
Volume 2
Issue 2
Date February, 2012
Keywords Dynamic, soil-structure interaction, infinite element, tunnel.

The objective of this paper is to investigate the validity of transmitting boundaries in dynamic analysis of soil-structure interaction problems. As a case study, the proposed Baghdad metro line is considered. The information about the dimensions and the material properties of the concrete tunnel and surrounding soil were obtained from a previous study. A parametric study is carried out to investigate the effect of several parameters including the peak value of the horizontal component of earthquake displacement records and the frequency of the dynamic load. The computer program (Mod-MIXDYN) is used for the analysis. The numerical results are analyzed for three conditions; finite boundaries (traditional boundaries), infinite boundaries modelled by infinite elements (5-node mapped infinite element) presented by Selvadurai and Karpurapu ,1988), and infinite boundaries modelled by dashpot elements (viscous boundaries). It was found that the transmitting boundary absorbs most of the incident energy. The distinct reflections observed in the "fixed boundaries" case disappear in the "transmitted boundaries" case. This is true for both cases of using viscous boundaries or mapped infinite elements. The type and location of the dynamic load are two controlling factors in deciding the importance of using infinite boundaries. It was found that the results are greatly affected when earthquake is applied as a base motion or a pressure load is applied at the surface ground. The horizontal displacement on the free surface increases significantly when modeling infinite boundaries at all values of peak displacement of the earthquake. It increases about (7.0) times the value of using finite elements only.

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