The Influence Of Input From Synthetic Ground Motion Field With Different Spatial Correlation And Coherency On Seismic Response Of Long-span Bridge

Seismic responses of a large span bridge are calculated from inputs consistent, traveling wave and non-consistent at the bases of the two supporting tower of the main span by my teacher’s research group, the results show the difference between these three input methods. This paper discusses the influence of ground motions from synthetic ground motion field with different spatial correlation and coherency on seismic response of long-span bridge. We build up a bridge model by the function of finite element software ANSYS with the design data of a large span cable based bridge. The free vibration characteristics of the bridge is analyzed by ANSYS. We also have the data of synthesized motion field from an earthquake with magnitude6.5on an active fault in Western China. Several pairs of ground points are selected from the motion field. We calculate the spatial correlation and coherency cofficient of ground motions and analysis its variation in different locations. Then we select some representative points in order to calculate the seismic response of the bridge and analysis the influence of ground motions with different spatial correlation and coherency on seismic response of the bridge. The main progresses are as follows.1.When the pair of the ground points are on a line parallel to the strike of source rupture plane, the spatial correlation and coherency coefficient of the pair of ground motions reduces with the decrease of the distance between the ground points and the main asperity.When the pair of the ground points are on a line perpendicular to the strike of source rupture plane, the coherency coefficient of the pair of ground motions with high frequency (3.0Hz) increases with the decrease of the distance between the ground points and the main asperity. The coherency coefficient of the pair of ground motions with low frequency (0.3Hz,1.0Hz) reduces with the decrease of the distance between the ground points and the main asperity. The change of the spatial correlation coefficient has no rule.2.The response results of the bridge on a line parallel to the strike of source rupture plane show some conclusions as follow. The lengthwise peak displacement of the main beam, the lateral displacement of the main beam, the horizontal average displacement of the main beam, the lengthwise and lateral displacement of the top of towers, the axial force of the main beam and the shear of the bottom of the towers increase with the decrease of the spatial correlation and coherency coefficient of ground motions. The lengthwise average displacement of the main beam, the horizontal peak displacement of the main beam and the moment of the main beam decrease with the decrease of the spatial correlation and coherency coefficient of ground motions.3.The response results of the bridge on a line perpendicular to the strike of source rupture plane show some conclusions as follow. The lengthwise peak displacement of the main beam, the horizontal average displacement of the main beam, the lengthwise displacement of the top of towers, the lateral peak displacement of the top of towers, the moment of the main beam and the shear of the bottom of the towers increase with the decrease of low frequency and decrease of high frequency of the spatial correlation and coherency coefficient of ground motions. The lengthwise average displacement of the main beam, the lateral displacement of the main beam, the horizontal peak displacement of the main beam, the lateral average displacement of the top of towers and the axial force of the main beam decrease with the decrease of low frequency and decrease of high frequency of the spatial correlation and coherency coefficient of ground motions.