Dynamic Response Analysis Of Structures With Base Isolation

The function of seismic base isolation,by connecting the upper structure with the base using earthquake isolator with low horizontal stiffness and certain damping,is to decrease the seismic shock energy transmitted from the base to the upper structure and its effect of damage on the building structure,and increase the seismic resistance ability of the building structure.The Ambulatorium Complex Building of People's Hospital of Lushan County in Sichuan Province is a base isolation building which was designed and constructed after Wenchuan Earthquake(Mw=8.0).In Lushan Earthquake(Mw=7.0)on April 20,2013,this building showed a strong seismic resistance ability by undergoing the earthquake shock of intensity 9,and confirmed its social and technical benefits in the emergency aid and treatment of the hospital after the main shock of the earthquake.At present,some textbooks and monographs illustrate seismic base isolation principal based on the linear vibration characteristics of structure with single degree of freedom,resulting that seismic isolation can decrease the acceleration of the structure while the displacement of the structure will be increased.For the analysis on the linear amplitude-frequency characteristics of structure with multiple degrees of freedom(DOFs),the analytical solutions are seldom reported.Based on the previous research results,for the dynamic characteristics of seismic base isolation structure with linear multiple DOFs,the research was carried out in this thesis.The research content and results of this thesis are as follows:(1)Assuming the ground motion of a 7 DOFs structure is a horizontal harmonic motion with a certain frequency,the analytical solutions of structure acceleration,absolute displacement,interlayer displacement are derived with hysteresis damping and viscous damping,respectively.The results on the seismic base isolation structure show that the calculation formula of seismic isolation transmission ratio of horizontal acceleration is the same as that of horizontal absolute displacement.Seismic base isolation can decrease the amplitudes of both acceleration and absolute displacement of the upper structure.However,seismic isolation transmission ratio of horizontal interlayer displacement amplitude is significantly different from that of horizontal acceleration.(2)Assuming the ground motion is a horizontal harmonic motion,parameter analyses based on the analytical solutions are performed.The results show that,the absolute displacement amplitude of aseismic structure increases significantly with the height of building.However,the absolute displacement amplitude in seismic base isolation structure is significantly smaller than that in aseismic structure due to the effect of seismic base isolation,and its increase with the height of building in seismic base isolation structure is significantly smaller than that in aseismic structure.Horizontal interlayer displacement amplitude decreases with the height of building in aseismic structure,however,it does not varies much with the height of building in seismic base isolation structure.The research also investigates the effect of seismic isolation damper on the seismic isolation and proposes a method to evaluate approximately the fundamental frequency of seismic base isolation structure.(3)Based on a linear model,the dynamic response of 7 DOFs structure is calculated for the horizontal seismic acceleration signal input of multiple frequencies by adopting direct integration method.The acceleration of seismic base isolation structure and the variation characteristics of interlayer displacement peaks with layers are investigated.Calculation examples show that the results based on direct integration method are qualitatively identical to those based on analytical solutions.The current research results based on the analytical solutions are of theoretical and practical significance on understanding the dynamic characteristics of seismic base isolation structure.It is suggested that experimental researches be performed in the future to evaluate the absolute displacement and its variation with the layers in the seismic base isolation structure.