Research On The Seismic Response Of RC Frame Structure Under The Mainshock-aftershock Ground Motions On Soft Soil And Near-fault Site

According to historical seismological data,about 89% strong shock will follow by fairly strong aftershock,the aftershock and the main shock will form mainshock-aftershock ground motions.The strong aftershocks will cause additional structure damages,which can lead to more serious seismic hazard,also structures and constructions tend to be not safe.Thus,those aftershocks will give rise to large amounts of casualties and financial losses in disaster areas.Also,because the ground motions present significant differences in spectral characteristic between soft soil site and normal site,the damage potential is quite different as well.Furthermore,because near-fault site ground motions include pulse signals,the structure damages are much greater than non-pulse ground motions.According to this phenomenon,this paper discussed and analyzed the feature of response and seismic fragility under soft soil and near-fault site mainshock-aftershock ground motions at Van Nuys Building.The major analysis contents are as follows:(1)Through the contrastive analysis of numerical simulation result and measured data from transducer which proves the Open Sees finite element model accuracy of Van Nuys Building.(2)Analyzed the feature of the frame structure's reaction(roof displacement,the peak of story drift ratio and the peak of residual story drift ratio)under soft soil sites mainshock-aftershock sequences,and the structure damage under different input sequences of ground motions,researches show that soft soil sites aftershocks caused much greater additional damage on structure than normal sites aftershocks.When mainshock-aftershock has a large earthquake magnitude,the reactions at soil sites are more drastic.The differences input sequences of ground motion's intensity cause varying degrees of structure damage.The components have a greater energy dissipation under the sequences that represent mainshock-aftershock's reverse sequence than the components under plain sequence.(3)Analyzed the reaction feature of the frame structure under the action of near-fault mainshock-aftershock sequences.Through setting up near-fault mainshock-aftershock sequence randomly,analyzed the near-fault ground motions polarity influence to the structure.The result shows that,the additional influences to the structure from near-fault pulse-like aftershocks are much greater than the far-fault non-pulse-like aftershocks.While the aftershocks happen and increase intensity,the angle of structure maximum reaction is changed.Also,use different index to measure structure reaction,the results are different at some point.(4)Analyze the vulnerability of the frame structure under the action ofmainshock-aftershock at soft soil sites and near-fault sites,and contrastively analyze the vulnerability of the frame structure under the action between normal sites,far-fault sites and soft soil sites,near-fault sites.The result shows that,a larger exceedance probability of structure damage exists under soft soil sites and near fault-sites aftershock,by contrast,for normal sites and far-fault sites,the vulnerability curve keeps the same before and after the process of mainshock-aftershock.