Modeling Of Dynamic Soil-Pile-Bridge Interaction

The seismic design of a bridge structure is based on the accurate analysis of the response of the bridge system to seismic excitation. At present, seismic design of most bridges are based on the assumption of fixed connection between foundations and the underlying soil, ignoring the influence of dynamic soil piles-bridge interaction. Simplified methods for calculating the dynamic stiffness and damping of pile foundation to the dynamic soil-piles-bridge interaction are studied in this thesis. The main contents of this thesis are as follows:(1) By literature review, the existing methods for addressing the dynamic soil-piles-bridge interaction are summarized and analyzed.(2) Based on the theory of one-dimensional wave propagation, the dynamic impedance of one-dimensional soil element in semi-infinite medium is analyzed. And the variation of radiation damping and material damping of pile- foundation with the frequency of vibration is illustrated.(3) The methods for calculating the dynamic impedance of single-pile by equivalent homogeneous soil method and layered superposition method are discussed. A method for calculating the dynamic interaction factors between two single-piles in pile groups is presented. A finite element model for considering dynamic interaction between pile foundation of bridge and underlying soil is proposed.(4) In order to verify the proposed model, a single pier for a high-speed railway bridge with pile foundation is taken as an example to calculate and analyz the dynamic impedance of the pile funoundation.. The natural frequencies and vibtation mode shapes and seismic responses of the pier with and without consideration of dynamic soil-foundation interaction are compared. The influences of dynamic impedance of single pile calculated by equivalent homogenization method and layered superposition method on dynamic response of pier are discussed. The results show that the stiffness of the structure decrease, the displacement and internal force increase when considering the dynamic soil-foundation interaction. So the seismic design of rigidity structures will be unsafe if the dynamic soil-foundation interaction is ignored.(5) With the proposed model, the free vibration properties and seismic responses of a cable-stayed bridge and a suspension bridge are analyzed. The dynamic performance of the cable-stayed bridge and the suspension bridge with consideration of the soil-foundation interaction is discussed and suggestions for seismic design of these bridges are presented.The results show that, for such a small span cable-stayed bridge with relatively large stiffhess, the displacement of the structure increase ,the internal force of some components decrease and of the other components are increased when considering the dynamic soil-foundation interaction.As for the large span suspension bridge, the displacement and internal force of the superstructure are reduced.