Soil-structure interaction analysis of cable-stayed bridges subjected to multiple-support excitations

In this study, it is intended to determine the effects of soil-structure interaction (SSI) and multiple-support excitation on the dynamic characteristics of the seismic response of cable-stayed bridges. For this purpose, ground motion time histories are simulated for multiple-support excitation, depending on the spatially varying components of incoherence, wave-passage and site-response effects. Each simulated time-history is generated to be compatible with the Eurocode 8 response spectrum normalized to 0.5g PSA. The substructure method which partitions the total soil-structure system into two substructures: the structural system and the soil system, is used to treat the soil-structure interaction problem. In order to investigate the soil-structure interaction effect on the response of cable-stayed bridges under multiple-support excitation, two-dimensional model of an existing bridge (Jindo Bridge) is used to represent the superstructure. To emphasize the relative importance of the spatial variability effects of the earthquake ground motion, bridge responses are determined for the fixed base bridge model which neglects the soil-structure interaction effect and for the bridge model which includes the soil-structure interaction effect. It is observed that both of the soil-structure interaction and spatially varying ground motions have important effects on the structural responses. The parametric study of the relative importance of the soil-bridge interaction in the presence of spatial variability components of the ground motion shows that the multiple-support excitation and soil-structure interaction should be considered in the dynamic analyses of cable-stayed bridges. The thesis prepared with this purpose includes the following chapters.In the first chapter, general information about the subject is given and the importance of the matter is outlined.In the second chapter, the aim of the study, previous studies about the subject and information about the content of the study are given.In the third chapter, the theoretical formulation about simulating ground motions is given along with the construction of the finite element model of the selected cable-stayed bridge. The flowchart of the modified computer program which includes the spatial variability of ground motion and the soil-structure interaction effect is also defined in this chapter.In the fourth chapter, the influence of the soil-bridge interaction and spatial varying ground motion effects on the selected cable-stayed bridge model is discussed depending on the obtained structural responses. As the results and recommendations obtained from the analyses are given in chapter five, this chapter is followed by the references.