Browsing by Author "Fourie, Dylan Andrew"
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- ItemRock-structure interaction : improving the consistency in the finite element modelling of rock foundations for bridges(Stellenbosch : Stellenbosch University, 2020-03) Fourie, Dylan Andrew; Fouche, Nanine; Van der Merwe, Frans; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: The design and modelling of foundations crosses two civil engineering disciplines, namely structural- and geotechnical engineering. The structural engineer goes into great detail when sizing foundations to ensure effective load transfer from the superstructure to the underlying geomaterials. This is usually accomplished by deriving the load and moment taken down from the superstructure onto the foundation. This load takedown is normally established as a first estimate based on either a fixed-base or an assumed springs stiffness model in structural finite element (FE). The loads transferred from the superstructure to the various piers and foundations will vary depending on the fixity assumed by the structural engineer and could result in large discrepancies when modelled with the same stiffness when certain foundations are stiffer than others. This becomes more critical in large bridge structures with tall piers where even the slightest differentials in displacement at the base of subsequent piers of the structure could lead to significant differential tilt and settlement at the top of the piers – resulting in significant load re-distribution between softer and stiffer foundations. It is therefore proposed that the analysis process is and should be an iterative process between the structural- and geotechnical engineer as settlement and distortion is best estimated by the geotechnical engineer whilst load take-down, due to these varying foundation stiffnesses, are best estimated by the structural engineer. This iteration should continue until convergence is reached between the two models. This study aims to compile a guideline to optimize the iteration process between the geotechnical- and structural engineer, and to assist the geotechnical engineer in improving the consistency in the finite element modelling (FEM) of the interaction between the structure and the rock. This was achieved by modelling a bridge footing on rock using a 3D geotechnical FE software package; obtaining the footing’s settlement and rotation; deriving structural springs and inserting these revised springs back into a structural FE software package to determine the revised load takedown. This allows for more realistic modelling by the bridge engineer. A simplified method was proposed of applying an eccentric loading, which provided accurate results when the footing was assumed to be fully rigid. The settlement values from the geotechnical model differed with less than 10% from the structural model. The derived springs, thus, model the rock-structure interaction more accurately and can be used for rigid and flexible foundations.