Stochastic analyses of base isolated highway bridges to spatially varying ground motions using friction pendulum system

SUMMARY Stochastic Analyses of Base Isolated Highway Bridges to Spatially Varying Ground Motions by Using Friction Pendulum System In this study, stochastic response of base isolated highway bridges subjected to spatially varying ground motions by using friction pendulum system are investigated. The ground motion model includes the effects of wave passage, incoherence and site response. Due to the complex nature of earth crust, the spatial variability of ground motions should be included in the stochastic analyses of bridges that have long span. Bridges are lifeline structures. In addition, the failure of bridges during earthquakes causes seriously consequences. The seismic forces on such structures can be reduced if the fundamental period of bridges is lengthened or if the energy dissipating capacity of bridges is increased. Therefore, the seismic isolation is an alternative design of bridges to protect from damages caused by strong earthquakes. The thesis prepared with this scope includes the following chapters. In the first chapter, general information, the importance of the matter, previous studies about the subject are given. Besides, the formulation of stochastic analyses of non isolated and isolated structures considering spatially varying ground motions is also presented. In the second chapter, the ground motion model used in the stochastic analyses is described. In addition, the analytical model of the highway bridge chosen as an example is taken place. The end of this chapter, the frequencies and mode shapes obtained from free vibration analysis of the bridge without and with isolation are presented. In the third chapter, response values obtained from stochastic analyses of non-isolated and isolated bridge to spatially varying ground motion are discussed. As the results and recommendations are given in the fourth chapter, the references are presented in the fifth chapter. As a conclusion it can be observed that base isolation and spatially variability of the ground motion have significant effects on base isolated bridges. So, these effects should be considered in the analyses of bridges with long span. Keywords: Base Isolation, Friction Pendulum System, Stochastic Analysis, Highway Bridge, Filtered White Noise, Incoherence Effect, Wave-Passage Effect, Site- Response Effect, Power Spectral Density Function, Spatially Variability. VII