Study Of Seismic Response Analysis Of Underground Structure In Active Fault Area

Recently, earthquakes occur frequently around the world. The strong ground motion simulation methods based on active faults have been proposed. After Kobe earthquake, the seismic response analysis method and theory of underground structures have been developed. To use the research results of seismology to promote the earthquake response analysis of structures is what we would focus on in this study. We try to connect the strong ground motion simulation and seismic response analysis of underground structures as a complete analysis system, which contains source (active fault)-structure. The proposed analysis system would provide a new way for seismic response analysis of underground structures. The main work in this study is shown in what follows:(1) The best source model and parameters of Wenchuan earthquake were derived using the records of aftershocks by empirical Green’s function method. The derived source model contains three asperities (strong motion generation area SMGA), the total area of which is close to the empirical parameter of Irikura and Miyake.(2) The corner frequency of a large earthquake differs from that of a small one. Assuming the corner frequency of each subfault is reversely proportional to the square root of the amount of ruptured subfaults, a new function is constructed based on ω2 source model. The dynamic corner frequency would be applied to the empirical Green’s function method by the proposed function, which could improve the low frequency content of simulated results.(3) The near fault strong ground motion is synthesized using the derived best source model by the revised EGF method. The peak ground motions of observation arrays around the source fault are compared.(4) Based on two dimensional elastic wave motions equation, two dimensional visco-elastic artificial boundary conditions for two wave source are derived. Numerical example demonstrate that two dimensional visco-elastic artificial boundary conditions for two wave source are validate. Then the derived visco-elastic ABC is promoted to three dimensional condition. The wave input for the derived ABC is equivalent load of nodes on boundary meshes. A 3D elastic material model is constructed with equivalent load on the boundary nodes. The displacement history of the observation point is compared with the analytic solution to demonstrate the validation of input equivalent load.(5) The seismic response of a subway station is analyzed using the strong ground motion of Wenchuan earthquake as input load. Three different input method are conducted. The earthquake loads are only set on the bottom boundary in case 1. The earthquake loads are set on five artificial boundary in case 2. The earthquake loads are set on five artificial boundary in case 3, and the loads are different from each other on the boundary. The results shows that the response of case 3 are different from that of case 2. The difference might be the peak value of the response and the position of the peak response. The maximum story drift angles of the structure are inversely proportional to the peak ground displacement of the input waves in semi-logarithmic coordinate system.(6) The affecting factors of the seismic response of underground structures are studied. According to the results, suggestion are proposed to decrease the deformation of subway station cross-sections. Increase of the rigidity of the cross section could effectively induce the maximum story drift. The maximum story drift deformation is not affected by the peak acceleration of the input waves. But the peak displacement of the input waves is related to the maximum story drift deformation of the underground structure.