The Analysis Of Vibration Isolation Performance With LRB Base- Isolated Frame Structure

Isolation technology is a kind of passive control technology, which, according to the different location of the isolation layer, can be divided into the base isolation and the interlayer seismic isolation. The base isolation technology has been widely used in aboard. Generally, the isolation devices are set at connection of the bottom of the column in the first layer and the foundation, consuming most of the seismic energy through the deformation of the isolation device to reduce the earthquake response of upper structure. The good seismic performance and reasonable economy of the isolation structure had caused high attention by the domestic construction workers, faced with a rapid developing stage. At present, there are more than 100 buildings using the laminated rubber isolation technology in Sichuan province. Kaidefengshang once was the largest community of base-isolated buildings. Up to now, our country has built more than 2000 base isolation buildings, in which the new Kunming airport is currently the world’s largest monomer isolation building. On the application area, in 2008 we surpassed Japan for the first time.From the viewpoint of a construction worker, this paper firstly introduces the basic knowledge of isolation technology, such as the present domestic and foreign research situation, the isolation principle, the isolation classification, the characteristics of isolation bearing, and the superiority and the applicable scope of isolation technology. The following is using the two kinds of isolation model: the single particle vibration isolation system model and the multi-particle vibration isolation system model to analyze the basic theory of seismic isolation technology, and a brief analysis of the general solving method of dynamic analysis. And the dynamic equilibrium equation is deduced and solved. Finally, by the finite element analysis software SAP2000,setting up a model of a six-story frame structure and its isolation model respectively to do the modal analysis, the dynamic time history analysis of the resistance earthquake and the severe earthquake. This article chooses two actual seismic waves and a synthetic wave to do the time history analysis, calculating the dynamic response of the two kinds of structures, respectively under the action of the resistance earthquake and the severe earthquake. Through comparing the response such as modal figure, inter-laminar shear, interlayer displacement, peak acceleration, of the two kinds of structures to the action of earthquake, the regularity of vibration isolation structure can be got.The main conclusions of the paper are as follows:(1) From the vibration period of the structure before and after isolation,it can be seen that compared with vibration period of traditional seismic structure the lead rubber bearing(LRB) base isolation structure’s vibration period under earthquake has been significantly prolonged. The prolonged vibration period of isolation structure has extended the vibration period of the structure away from the site predominant period, avoided the high energy band of seismic wave, significantly reduced the horizontal earthquake action transferring to the upper structure, and tremendously improved the safety of building structure.(2) From the front three order mode shapes of the traditional seismic structure and the isolation structure, the first and second modes of the two structures, under the action of earthquake,are translational. But the interlayer displacement of the traditional structure is much larger than the isolated structure’s interlayer displacement. And the third mode of the two structures is shown to reverse. The difference is that the traditional seismic structure torsion deformation is larger than the isolation structure. And the torsion deformation of the isolation structure mainly occurs in the isolation layer, through the large deformation of the isolation layer consuming most of the seismic energy, cutting off the transfer of the earthquake to the upper structure. The damping effect of earthquake is very obvious.(3) Although the shearing force of the traditional seismic structure and the isolation structure is much different in quantity, but the two structural systems both show the same trend: the higher the floor, the smaller the shear, the higher the decrease rate. The shearing force of the base isolated structure is 12%~35% of the traditional seismic structure. It can be seen that the isolation effect of lead rubber bearing is obvious. It is worth to be popularized, especially in some places such as schools, hospitals, exhibition halls, etc..(4) The horizontal damping coefficient of the isolation structure is 0.40β 0.25. And the horizontal damping coefficient to decreased one corresponding level of the seismic fortification intensity after the isolation is 0.40 β 0.27. So it can be seen that the seismic fortification intensity can be reduced and the upper structure can be designed according to 7(0.1g).(5) The maximum vertex acceleration of the isolated structure is about 1/2~4/5 of the traditional seismic structure. The isolation effect is significant, achieved the desired effect.(6) The maximum displacement of isolation structure occurred in the isolation layer. And the upper structure almost shifts horizontally. The displacement of the base isolator is very small compared with the traditional seismic structure, and the displacement reduce amplitude of each layer is different, the displacement reduce amplitude of the first layer is the smallest, the displacement reduce amplitude of the top layer is the biggest.In conclusion, the isolation building, through the contrast analysis, can effectively reduce the seismic response of structures,and the lead laminated rubber isolation bearings have good vibration isolation effect. At the same time, owing to the professional attribute of the isolation technology, it is the specialized personnel who is responsible for its design in strict accordance with the design steps. In order to ensure the good vibration isolation performance of the isolation building, it is necessary to develop the corresponding isolation building maintenance management plan, and be strictly implemented.