Stochastic analysis of cable-stayed bridges modelling coupled finite-boundary element methods

In this study, it is aimed to determine the stochastic behaviors in the cable stayed bridges subjected to spatially varying seismic excitation, using a coupled model based on Finite Element Method (FEM) and Boundary Element Method (BEM). In order to investigate the soil-structure interaction effect on the response of cable-stayed bridge under spatially varying seismic excitation, two dimensional model of an existing Quincy Bayview Bridge (USA) is selected as an example. A substructuring approach is used to model the bridge-soil dynamic interaction. In the coupling model whole domain is divided into two regions, namely boundary and finite element regions, with common interface. The bridge system is represented using finite elements, while the underlying layered soil medium is modeled using boundary elements. In order to join these two regions compatibility and equilibrium conditions must be satisfied along the interface. The boundary element formulation is presented for the dynamic analysis of two layered soil medium. The formulation is performed in Fourier transform space by using constant boundary element. Based on the formulation presented in this study, a computer code written in Fortran is used for two dimensional dynamic analyses of the layered soil medium. Equivalent finite element method is added to the computer code and is used to obtain equivalent stiffness matrix related to boundary element region. According to this method boundary element region is transformed as an equivalent finite element and the final system is solved as a stiffness problem. Thus, the dynamic behaviors of the bridge subjected to spatially varying ground motions considering soil-structure interaction are obtained.