Seismic Performance Of LRB Base Isolated Structure Considering The Influence Of Ground Motion Characteristics

The isolation system as a new type of structural aseismic system has been widely applied in the fields such as building,bridge and so on,and the test results of the isolated stru(?)ture subjected to many earthquakes show that the isolated effect is remarkable,and the seismic performance is better than that of the traditional seismic structure.The isolation devices with relative horizontal stiffness is small are installed in the isolation layer,which could keep the basic frequency of base isolation structure away from the high frequency components of the ground motion and reduce the seismic response of upper structure significantly,so as to improve the seismic performance of the structure.For the near-fault pulse-type ground motion and soft soil far field harmonic-like ground motion are two kinds of typical long-period ground motions,it can lead to serious damage of the long period structure due to the special nature of ground motion and the generation mechanism.Therefore,it is urgent to study on the seismic performance of the isolated structure under the special ground motion.For this reasons,this paper mainly focuses on the seismic response and seismic performance of the LRB base isolated structure under the action of the three types of ground motions such as near-fault pulse-type ground motion,ordinary ground motion and far field harmonic-like ground motion,the main contents of research work in this paper are as follows:(1)The spectral characteristics of common field ground motion and long period ground motion are analyzed.According to the existing research results of long period ground motion characteristics and its difference from the common field ground motion were analyzed and summarized,and the selection criteria of all kinds of ground motion are established based on this work,the equal intensity spectral characteristics of the single degree of freedom isolation system under the three kinds of ground motions are calculated.The results show that the displacement of a single degree of freedom isolated system is larger than the results of ordinary ground motions under long period ground motions;for the equal intensity spectrum,the damping ration in 0.05?0.2 have little influence on the acceleration response of the structure,and the peak value of displacement response decreases with the increase of damping ratio;the change of stiffness ratio has little effect on the equal intensity spectrum.(2)The inelastic displacement demand spectra of isolated bearing under common field ground motion is studied.By comparing response spectra of ground motion records and the code spectra,the problem of spectral shape and spectral amplitude distortion is found when the code spectra was used to predict the displacement demand of seismic isolation structure.Considering on the mechanical parameters of isolation bearing,ground motion characteristics and other factors influence on the displacement response spectra,the characteristics of displacement response spectra is studied by the method of standardization and average,and based on the elastic displacement spectra of Eurocode8,the inelastic displacement demand spectra of isolated bearing is proposed through the numerical fitting method,which can be used to predict the displacement demand of the isolation layer and to determine the type of bearing,simplify the design process.The result based on a practical engineering example shows that the displacement of isolation layer is calculated based on the formula of displacement spectrum proposed in this paper is in good agreement with the analysis results of the actual modeling.(3)The seismic performance of isolated structure and the failure rule under the long period ground motion are analyzed.At first,the isolated structure model is established by SeismoStruct software,and the response characteristics of isolated structure under near-fault pulse-type ground motion and far field ground motion are analyzed by the nonlinear dynamic time history analysis;then,the failure rule of superstructure is discussed based on the whole structural member from yield to failure;finally,a measure is proposed to prevent the damage of upper structure of the isolation structure and the feasibility of this approach is discussed.The results show that the long period ground motion can cause greater damage to structure than the ordinary ground motion under the equal earthquake intensity,and can also magnify the displacement response of the structure.The damage of long period ground motion on the structure is mainly concentrated in the bottom of the structure,especially the damage to the column is more serious,which is considered to be the relative "weak parts".The structure achieved a remarkable effect on shock absorption by setting up the steel support in the bottom of the structure,and the performance of the overall structure has been greatly improved,and the analysis results can be provided reference for the structure design of relative engineering.