Study On Response Spectrum Of Base Isolated Structure Under Near Field Earthquake

In this paper,the seismic isolation response spectrum of structures under near field earthquakes is studied.In order to obtain the elastic-plastic response spectrum of the base isolated structures under near field earthquake and performance-based seismic design for the structures.By establishing the differential equations of motion for the single degree of freedom elastic response spectrum.The motion differential equation and the basic formula of the elastic system are studied.The problems should be considered in the study of response spectrum are presented.The basic principle of seismic isolation structure is analyzed.Select the equivalent element calculation model according to the characteristics of the isolated structure.And according to the characteristics of lead rubber bearing,the Bouc-Wen model is chosen as the restoring force model.The elastic-plastic dynamic differential equation is established based on Bouc-Wen restoring force model.The numerical calculation method of dynamic response is analyzed,and the dynamic differential equation is solved by Newmark-? method.In order to obtain the response spectrum of the structure under seismic action.The basic characteristics of near-field ground motion are studied and its influence on the structure is analyzed.According to the principle of division of the near field and far field ground motion and the classification principle of the site classification,134 seismic waves selected from the American seismic database(PEER)were classified.According to the definition of the period of the ground motion and the characteristics of the ground motion,the characteristic period of each kind of site and the maximum value of the coefficient of ground motion are determined.This paper calculate the acceleration response spectrum with damping ratio of 0.05 and 0.2.Through the solution of the elastic differential equation,the relative acceleration response spectra of the various fields under the near field and far field ground motion are obtained.According to the relationship between the relative acceleration response spectrum and the horizontal influence coefficient,the horizontal influence coefficient spectrum under different site conditions was established.The least squares method is used to fit the horizontal influence coefficient spectrum,and the elastic influence coefficient response spectrum of the acceleration are obtained.It is found that the maximum value of the horizontal influence coefficient of near field is larger than that of the far field.On the basis of given strength reduction factor and damping ratio,the elastic-plastic differential equation based on Bouc-Wen restoring force model is solved,The isometric ductility demand spectra of the three types of sites under near-field and far-field ground motion are obtained.The equivalence intensity ductility demand spectrum is fitted,the relationship among R,? and T was established.The elastic plastic displacement spectra of three kinds of site conditions under near-field ground motion and far-field ground motion are established by using the relation of R-?-T and the influence coefficient spectrum of elastic acceleration.It is found that the elastic-plastic displacement spectrum spectral values of under near field earthquake is smaller than that under far field earthquake's,and indicates that the seismic isolation effect of structure under near field earthquake is better than that of far field.The compression and shear tests were carried out on LRB bearings.And the results of the LRB bearing compression test are analyzed.The stiffness of the bearing and the yield stress are calculated according to the experimental results.The experiment of shaking table for liquefied natural gas storage tank was carried out.Comparing the results of shaking table with the results of elastic-plastic displacement spectrum.It is found that the performance based response spectrum analysis is closer to the actual response of the structure,The rationality of the response spectrum proposed in this paper is verified,and indicates that the research results of this paper have certain engineering application value.