Optimizing The Isolation Layer Of Frame Structure

Traditional seismic structures resist earthquakes mainly in a hard way,but this kind of structures generally can not resist the greater intensity of the ground motion,so scholars put forward the building isolation technology.Isolation technology is mainly divided into base isolation and story isolation,among which the base isolation is more mature.With the deepening of the research,more and more advantages of the story isolation have been discovered,such as flexible location,can be used in coastal areas or flood-prone areas.This article mainly by story isolation and base + story isolation structure as the research object,using FNA method of the finite element software ETABS program to calculate different models in different types of ground motion under the action of interlaminar shear to calculate the corresponding earthquake-reduction coefficient,and the displacement of isolation layer and testing the safety of isolation bearing by tension failure,Finally,a more reliable seismic isolation scheme is obtained through data analysis.(1)Firstly,a nine-story traditional seismic model was established.On this basis,an isolation layer with LRB+LNR rubber bearing was added,and the base isolation structure and four story isolation structures with isolation layer located at the first,third,fifth and seventh floors(isolation layer located at the top of the seventh column)were established respectively.Four types of seismic waves(conventional,far field,near field without pulse,near field with pulse)were selected according to the requirements of the anti-seismic standard,and the corresponding earthquake-reduction coefficient of each model under different seismic conditions was calculated by using finite element software ETABS program.The results show that the five different isolated structures have a certain damping capacity compared with the traditional seismic structures,but the five story isolation structures with single isolation layer have poor damping capacity in the face of ground motion with pulse,and the isolation layer is easy to exceed the limit under the rare earthquake intensity.(2)Six double isolation layers were established,and the isolation layers were located at the first and third,first and fifth,first and seventh,third and fifth,third and seventh floors respectively.Four seismic isolation structures with one base isolation layer and one interval seismic layer were established,and the isolation layers were located at the top of the foundation column and first column,the foundation column and second column,the foundation column and third column,the foundation column and sixth column.The results show that compared with the story isolation structures with single isolation layer,the story isolation structures with two isolation layers hardly improves the damping capacity,and the bearing displacement of the six models all exceeds the limit under the condition of rare intensity;Compared with other schemes,the damping capacity of the base + story isolation structures had improved to some extent,but the bearing displacement of the four models is still beyond the limit under the condition of rare intensity;The isolation layer combined with LRB+LNR rubber bearings has a large probability of exceeding the limit in the face of ground motion with pulse.(3)The LNR natural rubber bearings of the isolation layer were replaced with HDR high damping rubber bearings with damping and large horizontal stiffness.Eight isolation models were established by combining LRB+HDR rubber bearings,and the isolation layers were located in the foundation,first layer,third layer,first layer,third layer,first layer and third layer,third layer and fifth layer,foundation and first layer,foundation and second layer,foundation and third layer respectively;Compared with the isolation model established by LRB+LNR rubber bearing combination,the isolation model with single isolation layer established by LRB+HDR has little difference in damping capacity,but isolated structure with double isolation layers established by LRB+HDR has considerable improvement in damping capacity.All eight LRB+HDR isolation models do not exceed the limit of bearing displacement under rare working conditions.(4)The vibration equation of the two-particle model was established,and the expression of the mean square value of displacement response of the two particles was obtained.The stiffness of the isolation layer was obtained by making the derivative expression of the mean square value of displacement response to be zero,so as to optimize the isolation layer;By optimizing the third-layer isolation model and fifth-layer isolation model,better damping capacity can be obtained at a lower cost;Although the damping capacity of the optimized isolation model with single isolation layer is improved to some extent,the damping capacity is still not ideal when it comes to the ground motion with pulse.Even the optimized foundation isolation scheme has tensile failure under the action of the ground motion with pulse.Further optimization of the base+story isolation model,optimized three isolation model respectively,the foundation and first layer,foundation and second layer and the foundation and third layer,the results show that the earthquake-reduction coefficient of optimized base+story isolation model can even be less than 50% when it comes to the ground motion with pulse,and the isolation layer displacement was not overrun,but because of considering the influence of ground motion with pulse,the diameter of the bearing outside the base isolation layer should be appropriately increased.