Study On Seismic Input Direction And Seismic Response Of Curved Girder Bridges Considering Local Topography

In recent decades,earthquakes,which occurred frequently in China,especially in the western region,has brought threats to people's lives and property.As a lifeline project of the people,the bridge,once it is destroyed in the earthquake,will have a major impact on the subsequent rescue work.Therefore,this paper has carried out some research on the most unfavorable input direction of the common curved beam bridge in mountainous area,in order to play a certain reference role in the future seismic design.And this article has carried out related research work on the following aspects:(1)by reading relevant literatures at home and abroad,the seismic response analysis methods of Bridges and the spatial response laws of ground motions are summarized.(2)by establishment of three three-span curved girder Bridges with different spans,finite element analysis on them can be carried out.,And based on the two most unfavorable input direction criteria of response component and combined response quantity,this paper explores the influence of multi-point input on the most unfavorable input direction of curved girder Bridges.As a result,when the multi-point input causes a certain phase difference of the ground motion at each supporting position,the most unfavorable input direction of the curved girder bridge will change obviously.However,with the gradual increase of the apparent wave velocity,the most unfavorable input direction will be consistent with the same input.(3)based on the viscoelastic artificial boundary theory,three different three-dimensional field models were established in distribution to discuss and consider the influence of ground motion under local topography and its influence on the seismic response of curved girder Bridges.The results show that both P wave and SV wave show amplification effect when local topography is taken into account.For the whole slope,the surface response does not increase gradually with the increase of slope,but it is larger than the seismic response of flat site under any slope.The seismic response of curved girder Bridges will increase with the gradual increase of the topographic slope,and the maximum response will be generated at the piers corresponding to the top or bottom of the slope.(4)based on the results of local terrains' influence on ground motion,the curve beam bridge model under the corresponding terrains is established.And based on the judgmentcriteria of the two different most unfavorable input directions,the curve beam bridge's most unfavorable input direction under the local terrains is discussed.Through all those reaches,the result can be drew that the most unfavorable input direction of curved girder bridge under local topography will change,and the change range of the most unfavorable input direction will gradually decrease with the gradual increase of topography gradient.Moreover,it is found that the change of terrain is not the main reason for the change of the most unfavorable input direction of curved girder bridge,in fact,the change of the most unfavorable input direction is more due to the change of the bridge's own shape after the change of terrain.