Study On The Damping Effect Of Seismic Isolation Based On Nominal Stiffness Ratio

Earthquake is a very destructive and devastating natural disaster,since ancient times,the human and the earthquake has not stopped the struggle,every major earthquake will cause heavy casualties and economic losses.Most areas in China are located between the Eurasian seismic plate and the Pacific rim seismic plate.The seismic waves are wide and the frequency is high.Most of them are shallow earthquakes.The traditional seismic thinking is a kind of "hard resistance" way,which mainly adopts the idea of increasing the structural stiffness to ensure that the structure can withstand the large earthquake force without collapsing under the action of earthquake.Although this method is effective,it i s not efficient and economical.With the research of structural seismic resistance,a kind of "soft resistance" seismic idea is put forward.The main reason for the effectiveness of foundation seismic isolation is that the relatively small horizontal stiffness of the isolation layer extends the basic period of the structure and achieves the effect of isolating the earthquake.The practical application results also show that the foundation seismi c isolation has excellent damping effect,and the foundation seismic isolation technology is a more efficient technology than the traditional seismic method.This paper mainly studies the upper level of isolation layer stiffness and the relationship between the structure stiffness to the influence of the vibration isolation effect,the ideal isolation effect is almost never happen after the upper structure deformation,the upper structure under seismic action is akin to a rigid body in a horizontal direction to do translation,most of the seismic energy is absorbed by isolation layer to the upper structure is almost not affected by the earthquake effect,however in actual situation,if in order to obtain ideal vibration isolation effect,isolation layer level stiffness is too small,displacement of isolation layer will be larger,and even exceed isolation bearing design allows maximum displacement,when the isolation layer level stiffness is bigger,Although the displacement of the isolation layer is limited,the isolation effect will be less than ideal,and the stiffness of different structures before the isolation is different,for those original structures with small stiffness,the damping effect may not be ideal under the same stiffness of the isolation layer.When the foundation isolation technology was first proposed,the relationship between the horizontal stiffness of the isolation layer and the stiffness of the superstructure was the focus of the research,and the dynamic response of the superstructure with different stiffness after the earthquake should be further studied.This paper mainly completed the following aspects of work:(1)The concept of nominal stiffness ratio is put forward.In this paper,the nominal stiffness related to the fundamental period of the superstructure is firstly proposed,and then the concept of nominal stiffness ratio is defined,that is,the ratio of nominal stiffness of the superstructure to horizontal stiffness of the isolation layer..(2)Definition of damping coefficient.According to the designed response spectrum curve,the ratio of the seismic impact coefficient between the structure after isolation and before isolation is defined as the damping coefficient.(3)Damping coefficient curve.The curve of the nominal stiffness ratio of the superstructure with different nominal stiffness and the damping coefficient of the superstructure with different nominal stiffness was calculated.(4)In order to verify the rationality of the variation of the damping coefficient with the nominal stiffness ratio,a 9-storey frame model was made from the similarity relation,and the stiffness of the isolation layer was designed according to the predetermined damping target obtained from the damping coefficient curve,then the shaking table test was carried out.Test input acceleration is respectively 70 gal,125 gal,220 gal EL Centro wave and Taft wave simulation frame model under small earthquakes,and major earthquakes in the dynamic response of acceleration response of the upper structure with vibration pickup acquisition,test results show that the damping effect,has a good basic shock target in line with expectations,nominal rigidity ratio of damping coefficient curves for vibration isolation design for your reference.(5)Use Matlab to compile the dynamic time-history analysis program,analyze the isolation model,compare the analysis results with the test results,and provide certain reference.