Base Isolation Structure Under Long-period Ground Motion Damage Process Research

Seismic isolation technology is a kind of efficient passive vibration control technology,which is widely used in the field of engineering seismic.The data show that the isolation structure will be damaged in different degrees under the action of long period earthquake.At present,most of the research results on structural seismic damage process focus on the common ground motion or the traditional structure type.However,there are few studies on the damage evolution process of isolated structures under long period ground motion.Therefore,this paper selects multiple Far-field long-period ground motion,near-fault pulsed ground motions and multiple ordinary ground motions for comparison.The finite element model of RC frame foundation isolation structure is established.Dynamic time-history analysis is used to obtain response parameters.Based on the modified deformation and energy two-parameter damage model,the seismic response and damage process of base-isolated structures subjected to long-period earthquakes are studied.The main research contents are as follows:（1）Based on the ground motion strong holding time,peak ratio,response spectrum and Fourier spectrum,it analyzed the spectrum and energy characteristics of three kinds of ground motion by Hilbert-Huang transform.It is found that the platform segment of the acceleration response spectrum of ordinary seismic waves is short.The amplitude of the reaction spectrum will decay rapidly after reaching the peak point.However,the spectral values of the two types of long period ground motion accelerations attenuate slowly and the peak point of the spectrum moves back.The peak value of Hilbert amplitude spectrum of long period earthquake is larger than that of ordinary earthquake.Both instantaneous and cumulative energy spectrum values are larger than those of ordinary ground motion.The frequency band is concentrated in the low frequency region of 0.1～1Hz.（2）Based on the RC frame base isolation structure established by SAP2000,the dynamic time-history analysis method was adopted to compare the seismic behavior characteristics,energy distribution and dissipation of the base isolation structure under three kinds of ground motions.Under the long period ground motion in the near field and far field,the displacement of each layer and the displacement Angle between layers of the base isolation structure decrease gradually upward.The displacement of isolation layer is the largest,but it does not exceed the limit.Weakly layered structure is defined as the displacement Angle between layers exceeds the limit of elastoplastic displacement Angle.Compared with the two types of long period ground motion,the modal damping energy dissipation and the hysteretic energy dissipation of the unit are larger in the energy composition under ordinary ground motion.Under the rare earthquake condition,the modal damping dissipation energy of the structure under the selected two types of long period ground motion is greater than the hysteretic dissipation energy.The hysteretic dissipation of the structure under ordinary ground motion is larger than the modal damping dissipation.This situation is reversed under the condition of frequent earthquakes.（3）Based on the modified two-parameter damage model of deformation and energy and the hierarchical damage model,it uses MATLAB to calculate the damage index of the isolation structure components,isolation layers and the whole structure under the action of long period and ordinary earthquakes.Based on the selected damage criterion,it evaluates the damage degree of the base-isolated structure at each major time step.The results show that the damage of the bottom and the isolation layer develops faster under the near-field and far-field long period vibration.The damage failure of the bottom layer of the superstructure occurs earlier than that of the isolation layer and the damage development of the beam is faster than that of the column.（4）It describes the damage evolution and development of base-isolated structures in terms of seismic duration and structural space.It arranges the damage development paths of the beam,column and isolation bearing which are most seriously damaged under different earthquake action.The damage evolution curves and formulas of components,isolation layers and structures are fitted.It is found that the damage of isolating beams,column members and isolating supports increases rapidly in the late period of long period ground motion,but slowly in the late period of ordinary ground motion.