Analysis of railway bridges considering soil structure interaction

The purpose of this thesis is to investigate the dynamic behavior of an existing railway bridge in Turkey, subjected to different earthquakes considering different types of soils. In this study, the earthquake response characteristic of a multi span railway bridge was analyzed by taking into account the soil-structure interaction. For time domain dynamic analyses of the structure-soil model, a 2D version of PLAXIS, a specially developed finite element software for solving geotechnical problems, have been performed. In the analysis, two dimensional finite element (FE) model was used. Considering the soil property of bridge site, analysis was performed for three types of soil; the soils were specified as a soft, medium and dense. In this study three types of earthquake was used as input motion. In order to measure the effect of different ground motions as dynamic effect (different frequency content and acceleration amplitude); time-acceleration records of three different earthquakes are used. Kobe (Japan, 1995), Kocaeli (Turkey, 1999) and Manjil (Iran, 1990) earthquakes are defined as input motions. In order to determine the dynamic behavior of the bridge pier-soil system, analysis is carried out for different soil conditions with different stiffnesses. According to the results of the dynamic analysis, the dynamic responses of the bridge, including the horizontal displacements for the base and top points of the bridge pier and also for the middle and corner points of the soil are obtained comparatively and showed in graphic forms. Examining the results, it has been observed that the frequency content of the external load and the mechanical properties of the soil largely affect the dynamic behavior of the bridge pier and the maximum horizontal displacements differ when considering soil-structure interaction.