Seismic Response Analysis Of Long-span Bridges Subjected To Spatially Non-uniform Seismic Ground Motions

The non-uniform effects of long-span bridges under spatial variation of ground motions can not be neglected, and oblique incidence plays a vital role in triggering such spatial variation. In this thesis, the numerical simulation method of free field under oblique incidence is researched, and the response characteristics of oblique incidence earthquake motion field under different wave motion inputs, different geological parameters and river valley terrains are investigated. Afterwards, a three-dimensional FEA model considering the spatially non-uniform ground motion is built to analyze the seismic responses of a certain continuous rigid-frame bridge with large span, and the parameter analysis is carried as well. The main tasks and results obtained are as follows:(1) Based on the local artificial boundary, the input method of oblique incidence ground motion has been researched. With the help of one-dimensional change algorithm and the lumped-mass motion equations of artificial boundary nodes, the valid input program, which transforms the non-uniform seismic ground motion into equivalent forces loaded on the boundary nodes, is compiled by MATLAB language. Moreover, the auxiliary application programs could be written by the parameterized design language APDL of the FEA software ANSYS. Given the model’s parameters and incident seismic waves, the equivalent forces can be computed and automatical input can be realized, thus laying a foundation for the dynamic analysis of sites and structures under non-uniform seismic ground motion.(2) Take oblique incidence into account, the response analysis of free field were performed under single layer soil, multi-layer soil and soft soil layer with different shear wave velocities respectively. A two-dimensional FEA model of a typical valley terrain is established to analyze its terrain influence under P-wave and SV-wave. Further more, the effect of oblique incident seismic wave on local site is analyzed, and is compared with those of vertical incident seismic wave.(3) On the background of a crossing sea continuous rigid frame bridge, the seismic analysis of long-span bridge was presented and the amplitude and distribution of internal forces were studied. When influencing factors like seismic wave input, oblique incident angle and shear wave velocity of the soil were changing, the dynamic response influencing laws of continuous rigid frame bridges under P-wave and SV-wave were summarized.