Spatial Variation Of Seismic Ground Motions Modeling And Influence On Bridge Structure

Spatial variation of seismic ground motions modeling and influence on seismic responseof bridge structure are studied. The relative performance of two methods, Deodatis’ methodand Vanmarcke’s method, to generate time histories of multiple supports is investigated.According to EI-Centro(1940) and Kobe (1995) earthquake record, acceleration time historiesare generated by utilizing the selected method. Then, Contrast three non-uniform excitationanalysis methods, the relative motion method, the large mass methed and the large stiffnessmethod, to select solving method. The large mass methed is able to yield results that areidentical to those of the the relative motion method, and it’s realization is convenient bycomputer programs application. A continuous rigid frame bridge, suspension bridge andmulti-span bridge subjected to earthquakes are taken as cases to study in the influence law ofspatial variation on seismic response of bridge. The work done in this paper are listed asfollows:(1) To investigate the relative performance of Deodatis’method and Vanmarcke’s method,the waveform and wave intensity of time histories, generated by two methods in two cases(simulation conditioned by one specified record and cumulative simulation), are compared.The results show that Vanmarcke’s method can considere the full spatial variation when usingearthquake records in the engineering practice, providing the necessary input ground motionsfor the seismic design of practical engineering.(2) To verify the differences and practical applicability of the relative motion method(RMM), the large mass method (LMM) and the large stiffness method (LSM) widely used inmultiple-support seismic excitation analysis of structures, numerical simulations of amulti-span bridge model are performed according to the RMM, the LMM and the LSMrespectively under seismic ground motion excitations. It is also validated that the LMM canyield results that are identical to those of traditional theoretical methods, and LSM can not.(3) For this situation of inadequate consideration on the spatial variability in the currentbridge seismic analysis, time histories of seismic excitation generated by Vanmarcke’s methodand in consideration of full spatial variation are exerted on supports of a continuous rigidframe bridge, a suspension bridge and a multi-span bridge. The numberical results show that:the wave passage effect is only a factors of spatial variation, cannot completely replace theinfluence of spatial variation, ignoring the rest effects will underestimate the seismic responseof bridge structure, which is unconservative for seismic design.