Analysis Of Dynamic Characteristics Of Base-isolated Structures Under Long-period Ground Motion

Among the current energy consumption and vibration reduction technologies,the application of isolation technology is becoming more and more widely used.It is one of the most commonly used and very effective methods.This method is reliable,effective,and economical.Traditional non-isolated structure.Among the currently available seismic records,there is a type of ground motion with rich low-frequency components,large periods,and energy concentrated at low frequencies.This type of ground motion has significant long-period characteristics and is called a long-period earthquake.Dynamics,such as near-fault pulsed ground motions and far-field simple harmonic ground motions.If the excellent period of such long-period ground motions is similar to the natural vibration period of the isolation structure,resonance-like vibrations may occur,thereby amplifying the structural isolation layer The deformation of the seismic isolation layer causes deformation beyond the design expectations and damages,thereby reducing the seismic effect of the structure.In the design of various types of seismic isolation structures,due to the fact that the impact of long-period ground motions has not been fully considered in the design codes of China,the response and seismic isolation effects of the seismic isolation structures under the action of near-and far-field long-period ground motions are compared,Becomes particularly important.Based on the above ideas,the main research contents of this article are as follows:(1)Comparative analysis of the three basic elements of near-field and far-field long,period ground motions,it is concluded that PGA,PGV,and PGD of near-field long-period ground motions are the largest compared to far-field long-period ground motions,and long-field long-period ground motion The PGA value of ground motion is relatively small.A preliminary study of the differences in the duration of long-period ground motions.The absolute duration of the ground motion is used to define the duration to calculate the relevant ground motion durations.The research results show that the durations cannot distinguish the near-field and far-field long periods well.Earthquake.As far as the response spectrum is concerned,compared to the far-field long-period ground motion,the near-field long-period ground motion acceleration response spectrum value is higher and has obvious differences,while the far-field long-period ground motion spectrum value is lower and tends to be stable;the near-field long-period ground motion displacement response spectrum value is higher and has a comparison Significant differences.The peak value of the Fourier spectrum of long-period ground motion is generally in the range of 0?1 Hz.From the aspect of peak size,the amplitude of long-period ground motion acceleration is small,and the peak value of far-field vibration acceleration is generally smaller than that of near-field vibration.Long-period ground motion is mainly concentrated in 0Hz?2Hz.(2)Establishing an equivalent two-degree-of-freedom system model of seismic isolation,considering the impact of ground motion strength,analyzing the structural response of the two-freedom simplified model with different natural vibration periods,and using the maximum displacement of the isolation layer as the structural response parameter The correlation between the dynamic parameters and the response parameters of the isolated structure,and further analysis of the discreteness of the ground motions and structural responses of different intensities;the results show that the Chi-chi far field strength index D/V and the response of the long period structure(greater than 3 s)The sensitivity is strong,and the correlation between the index and the seismic response of the structure shows a strong periodic dependence;the characteristic parameters of the ground motion spectrum have a high correlation with the medium and long period structural response.Consider the level of correlation in the strong correlation range.It is recommended to select PGD for the near field strength index and DSI for the far field strength index.(3)Use OpenSees to establish a multi-layer isolated structure model,and adjust the natural vibration period of the isolated structure by changing the stiffness of the isolated support,A total of three(model A,B,C)isolation structure models,Then take the selected 10 near-field long-period ground motions and 10 far-field long-period ground motions as input ground motions,and then the dynamic time history of the structure is analyzed.The results show that:under the action of two kinds of ground motions,the response of the isolated structure is relatively large,and the response of the superstructure shows a flexural expansion trend,but the expansion trend of the far field is closer to that of the near field.The protection of the superstructure is weakened.With the reduction of the rigidity of the isolation support(model A-model B-model C),the response of the superstructure gradually increases from a trend of expansion to a straight line;the seismic response of the superstructure is relatively large Mainly concentrated in the 1-3 floors,with the reduction of the rigidity of the seismic isolation support,the weak layer has a downward trend.After the seismic record and the structure reach resonance,the response effect of the seismic isolation structure is further increased.From the perspective of the structural response of the three-model and long-period ground motion resonance in the far field,the displacement of the seismic isolation layer will increase by 40%or even more than 50%,and the displacement angle between the weak layers will increase by 30%or more than 40%.