Study On Seismic Performance Of Mountain Isolated Building Frame Structure Under Near-Fault Ground Motions

Scholars at home and abroad have been interested in near-fault ground motionsthese years since there were some big earthquake in recent years,such as Northridge andChi-Chi earthquake and so on,and there have been some useful conclusions.The distinctlong-duration pulse motion of ground velocity in the near-fault region may cause theadverse influence on the seismic performance of the base isolation building.So in thepresent paper,it will be discussed that the the earthquake response of SSI base-isolatedbuilding under near-fault ground motions.This thesis involves the following work:1.Three earthquake records from the Taiwan Chi-Chi earthquake on the same soilsite are chosen,including two near-fault earthquake TCU068and TCU054,and one farfield earthquake ILA007.The fault distance of two near-fault ground motions are all lessthan10km,wich pulse motion of ground velocity is included in,and the distance of thefar filed earthquake is more than100km. PGA of the three seismic waves is scaled on400gal,which spectrum analysis is carried out on in order to compare the pectrumcharacteristics.It is found that rich low frequency component is included in near-faultgroud motions,which will cause adverse influence on long-period structure,and richhigh frequency component is included in far filed groud motions,which will adverselyeffect on short-period structure.2.The two-dimensional SSI base-isolated and no isolation building models areestablished based on ANSYS. The time history analysis is carried out on the SSIbase-isolated and no isolation building under the seismic wave which is describedabove.It is found that isolation bearings can play a cushioning effect under near-faultand far field ground motions,of which the damping effect under near-fault groundmotions is poorer. The the earthquake response of the SSI base-isolated building undernear-fault ground motions is larger,under which the earthquake input energy of SSIbase-isolated building is more than the SSI no isolation.3.The two-dimensional SSI multilayer ground base isolation and story isolation, andno isolation building models are established based on ANSYS. The time history analysisis carried out on the three buildings above under the seismic wave which is describedabove on three categories such as hard and soft and hard soft soil site.It is found thatisolation bearings can play a cushioning effect on the floors above the scarp undernear-fault and far field ground motions,of which the damping effect of story iaolation is better than base isolation.However, the damping effect of the isolation bearings on thefloors below the scarp is varied with the soil stiffness. It is also founded that themultilayer ground building with no isolation is greatly influenced by site, but the twoisolated buildings are not,of which the isolation bearings weaken the influence of soilstissness. In addition, the earthquake response of SSI multilayer ground base isolationand story isolation buildings is greater under near-fault ground motions than far fiedground motions, and the damping effect of the isolation bearings under near-faultground motions is poorer.4. Different characteristics of near-fault ground motions from Taiwan Chi-Chiearthquake is chosen, which spectrum analysis is carried out on.It includes the influenceon seism response of SSI Multilayer groundbase isolation building of hanging-wall andspeed pulse and rupture directivity,and vertical accelerational effect. The seismresponse of SSI multilayer ground base isolation building is found different, which ismuch greater under hangning-wall than footwall ground motions if the PGA ofearthquake is not scaled, but the result is the other way around if the PGA is scaled at400gal. It is also found that under the ground motions with rupture forward directivitythe seism responses is the graeter followed by ground motion with fling-step, and theground motions without pulses is the smallest. In addition, the normal component offault is greater than the parallel under which the seism response of SSI multilayergroundbase isolation building. At last, the vertical response of structure is the greatestunder near-fault ground motion with pulses including full horizontal and verticalseismic component, so the strain produced by isolation bearing under near-fault groundmotions including pulses should be taken attention.