Seismic Response Of A Single-Tower Cable-Stayed Bridge With Dynamic Soil-Structure Interaction

Cable-stayed bridges have strong spanning capacity and beautiful appearances. As important components of transportation, once a cable-stayed bridge is destroyed or ruined in an earthquake, transportation will have to be interrupted, and serious damage of facilities and even loss of life will be incurred. The frequently happened earthquakes in China over the past years make the seismic analysis of a bridge structure a significant step in the design process.In this thesis, the effect of dynamic soil-structure interaction on the seismic response of a single-tower prestressed concrete cable-stayed bridge is studied and the finite element method is employed to model the behavior of the cable-stayed bridge under seismic excitation. The following aspects are addressed:(1) The usual physical models of dynamic soil-structure interaction are reviewed and analyzed;(2) Two models of dynamic soil-structure interaction, the six-spring model and the distributed springs model, are adopted respectively to analyze the free vibration of the cable-stayed bridge. The result shows that both fundamental frequency and higher frequencies decrease after taking the dynamic soil-structure interaction into consideration, and the order in which high vibration modes are excited also different;(3) Seismic waves are inputted to the computational model of the cable-stayed bridge in two combinations, respectively:longitudinal plus vertical direction and lateral plus vertical directions. The seismic response of the cable-stayed bridge with fixed supports is computed and the results are compared with those involving the dynamic soil-structure interaction. It turned out that if the dynamic soil-structure interaction is not considered, the earthquake-resistant design of the cable-stayed bridges could be in the unsafe side;(4) The seismic responses of the cable-stayed bridge under both the uniform support and multi-support excitation are computed and compared with each other. Also the effect of varying seismic wave velocities on the seismic response of the bridge is analyzed. It is shown that in the design of the seismic response of a single-tower prestressed concrete cable-stayed bridge, the effect of the dynamic soil-structure interaction on the behavior of tower and the girder cannot be ignored and the travelling wave effect should be taken into consideration.