Study On The Seismic Response Of Story Isolation Buildings Under Long-period Ground Motions

Due to the isolators, the structural vibration period was extended. Under the action of short period ground motion, the isolation structure generally can show excellent anti-seismic performance, but under the action of long period ground motion, seismic response of the structure will be quite a disadvantage. At present, the researchers concentrated most their energy on base-isolated structure, but the amount of the research about story isolation structure is relatively small. And most of the current research based on short period ground motion, moreover the exploration about the seismic response of isolated structure under the action of long period seismic is accountable.In recently years, structural damage caused by long period ground motion occurs frequently, and our country is promoting the application of isolation technology, with the development of isolated technology, the study on the negative response of the story isolated structure caused by long period and short period ground motion is very important. In this paper, on the basis of results of predecessor’s research, the author made an in-depth study on the seismic response of the story isolated structure which affected by long period and short period ground motions. The main research contents and conclusions of this paper are as follows:First of all, according to the purpose of this study, we made a selection criterion of long period and short period ground motion, chose the seismic wave based on the criteria, and inspected the spectrum characteristics of these seismic waves. Investigation found that, compared to the spectrum of long period ground motions, the spectrum of short period ground motions exhibited a strong regularity. This leads to the response of the structure caused by short-period ground motions are easily be predicted, but the seismic response of the structure generated long-period ground motions are difficult to predict.Secondly, establish a series of different mass ratio structures, control the structural natural vibration period through the changes of mass ratio. Input the selected long and short period ground motion to each building in order to do the nonlinear time history analysis. Investigated the difference and the laws of seismic response of each building, on this basis, did the further study on how mass ratio affected seismic response. The study found that, under the action of long period ground motion, the response of the story isolated structures between various aspects (the top speed, interlayer shear, interlayer displacement Angle and maximum displacement of isolation layer) were significantly greater than the corresponding response of short period ground motion. Maximum displacement of isolation layer, in particular, under the action of long period ground motion, the maximum displacement of isolation layer entered the overrun area, and when the mass ration is relatively large, the maximum displacement of isolation layer developed into the hazardous area, seriously affect the vertical bearing capacity of the story isolated structures.under the action of short period ground motion the response of each structure was basically increasing with the decrease of mass ratio (that is, the natural vibration period of shortening).While under the effect of long period ground motion, the seismic response of each structure is changing with different mass ratio has no fixed pattern. Need to consider it separately. This is mainly due to the large differences between the spectrum characteristics of long period ground motion. So, deepen the study of long period seismic spectrum characteristics, statistical form a long period ground motion response spectrum plan can serve as a focus of future research directions.In summary, firstly, this paper analyzed two types of ground motion features and differences in spectral characteristics. Then, we made a research on the differences of seismic response which generated by the two types of seismic waves. On this basis, analyzed how the mass ratio affected the seismic response of each structure. Finally, we get a number of relevant conclusions. These conclusions can be expected to provide a reference to enrich and develop the theory of seismic isolation.