Seismic Performance Analysis Of Multi Story RC Frame Structure Under Near Field Earthquake

Due to the special geographical location of our country,the seismic fault zone is very active,and the probability of near-field earthquake is high.The existing earthquake damage shows that near-field earthquake will bring huge loss to human society.However,the seismic design in the code for seismic design of buildings in China does not distinguish between near-field and far-field,and the area near fault is still based on far-field seismic design.Only in the aseismic performance-based design of building structures in article3.10.3 of the code,it is mentioned that for the structures within 10km of both sides of the seismic fault,the ground motion parameters should be taken into account in the near-field effect,and the increase factor of 1.5 should be multiplied within 5km of both sides of the seismic fault,and the increase factor of no less than 1.25 should be multiplied beyond 5km of the seismic fault,and whether this factor is reasonable is still worth discussing.Therefore,this paper chooses the representative multi-storey RC frame structure with fortification intensity of 8 and 9 as the research object,and discusses the rationality of the seismic parameters increase coefficient of 1.25 and 1.5 and the division of near-field area distance proposed in 3.10.3,in order to provide reference for the seismic design of similar projects in near-field area or the revision of the new code on near-field area structure design.The main research contents and conclusions are as follows:（1）Referring to article 3.10.3 of the code,considering the near-field effect of the ground motion parameters,six RC frame structures withα_max increasing coefficients of 1.25,1.5 and 1.75 in the 8 and 9 degree regions are designed.The numerical models of these six frames are established in Open Sees software,and the numerical modeling methods used in this paper are verified.It is found that the results of numerical simulation fit well with the test results,which shows that the modeling method and analysis method used in this paper have certain reliability.（2）The near-field impulsive seismic waves with epicenter distance of 0～5km and 5～10km are selected.The seismic performance of the frame designed in this paper is analyzed by using IDA method and seismic vulnerability method.The results show that:the increase of response spectrum can improve the seismic performance of the structure significantly;when considering the near-field pulse effect,it is not necessary to distinguish the epicenter distance of 5-10km and 0-5km;the frame of degree 8 and 9 designed withα_max increase coefficient of 1.25 and 1.5 can not meet the requirements of small earthquake and medium earthquake repairable;the frame of degree 8 and 9 designed withα_max increase coefficient of 1.75 The frame of 9 degree area can keep good seismic performance in the whole earthquake process.（3）Based on the nonlinear time history analysis of the coupling of vertical earthquake and horizontal earthquake,the change of displacement angle and the minimum axial force of frame column between the lower layers of vertical earthquake with different intensities is studied,and the following conclusions are obtained:the influence of vertical earthquake on the horizontal displacement of frame structure is almost negligible compared with that of horizontal earthquake;the design response spectrum is adjusted according to the amplification coefficient of 1.75 The 8-degree and 9-degree frames are enough to resist the horizontal pulse effect and the vertical seismic amplification in the near-field earthquake.