Study On Near Fault Seismic Response Spectrum Characteristics And Its Influence On Response Of Simply-supported Girder Bridges

For a long time,observations of near fault ground motion near faults have been very limited.The current seismic design code for bridges is mostly based on seismic ground motion records from far faults earthquakes.This means that the current design response spectrum cannot reflect well the seismic motion and structural response characteristics in the near-fault region,which may lead to unsafe conditions for bridges located in these areas.In addition,actual earthquake damage shows that structural performance requirements significantly increase under near-fault earthquake action.Therefore,studying the seismic design spectra for bridges in the near-fault region and the structural response of bridges under near-fault earthquake action is of great importance for seismic design of bridges in these areas.Based on this,the main research contents and conclusions of this paper are as follows:(1)Detailed classification and response spectrum calculation were carried out for544 sets of actual near-fault horizontal ground motion records,and the corresponding near-fault horizontal ground motion acceleration response spectrum was obtained.The standard acceleration design response spectrum for near-fault horizontal ground motion with a guaranteed rate of 84% was given by steps such as normalization,averaging,and least-squares segmentation fitting.(2)519 sets of actual near-fault vertical ground motion records were classified according to site categories.The standard acceleration design response spectrum for near-fault vertical ground motion with a guaranteed rate of 84% was given using the same processing method as for near-fault horizontal ground motion.(3)The structural response of two simply-supported girder bridges with different characteristic periods under the near-fault horizontal fitted acceleration response spectrum,the actual near-fault ground motion acceleration response spectrum,and the standard design acceleration response spectrum was analyzed.The rationality of the near-fault horizontal standard design response spectrum was verified,and the recommended near-fault horizontal standard design response spectrum was given based on safety and economic considerations.(4)Using the same analysis method as the horizontal one,based on the analysis of the response of the simply-supported girder bridge under the vertical ground motion near the fault,the rationality of the standard design response spectrum of the near-fault vertical is verified,and the recommendation for the standard design acceleration response spectrum of the near-fault vertical is given.