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Dynamic soil-structure interaction of simply supported high-speed railway bridges

Time: Fri 2020-09-25 13.00

Location: Via Zoom --, Du som saknar dator/datorvana kan kontakta / Use the e-mail address if you need technical assistance, Stockholm (English)

Subject area: Civil and Architectural Engineering, Structural Engineering and Bridges

Doctoral student: Johan Lind Östlund , Bro- och stålbyggnad

Opponent: Professor Rui Calçada, University of Porto

Supervisor: Professor Jean-Marc Battini, Bro- och stålbyggnad; Researcher Andreas Andersson, Bro- och stålbyggnad; Researcher Mahir Ülker-Kaustell, Bro- och stålbyggnad

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Research performed on the subject of dynamic soil-structure interaction (SS) concerning railway bridges is presented in this thesis with the focus on simply supported railway bridges supported by shallow foundations in soil strata on bedrock. The research aims to obtain insight into the SSI of high-speed railway bridges and to provide recommendations on how to model the soil-bridge system from a design perspective.

A three-dimensional (3D) simply supported soil-bridge model was first developed and the effects from model assumptions made on the soil-foundation system was evaluated in a 3D setting (paper I). The soil-foundation system was then refined and a model assumptions study was performed in order to evaluate the effects of model assumptions on impedance functions, including the influence of the permanent load acting on the soil-foundation system (paper II). Finally, a study of the assembled soil-bridge system was performed in an extensive parametric study including a set of 2D bridge models in combination with a set of shallow foundations in soil strata on bedrock (paper III). A supplementary section related to paper III was also added in this thesis, showing the effects of the substructure mass.

The model assumptions made when creating the soil-foundation model and the soil-bridge model can be very important and must be made with care. The permanent load acting on the soil-foundation systems of shallow foundations may alter the impedance functions significantly. The substructure mass may alter the behavior of the soil-bridge system depending on its magnitude, and neglecting it gives inaccurate results. The 3D effects of SSI do not cause high vibrations due to modes other than the first bending mode, and assuming a 2D bridge model is generally acceptable.

The effects of SSI on the soil-bridge systems with shallow soil strata are largely dependent on the ratio between the natural frequency of the bridge and the fundamental frequency of the soil. Depending on the value of this ratio, the effect of including SSI in bridge models may contribute to the bridge obtaining a negligible, conservative, or non-conservative response, as compared to the bridge with the assumption of non-flexible supports.