Research On The Overturning Of The Metal Isolation Bearings

China now is in the period of high development about urbanization,but many data and fact have showed that earth maybe enter the active period of earthquakes.The traditional anti-seismic method is no more available, the new isolation technology is greatly potential and will be developed fast. In so many isolation technology, the rubber bearing isolation technology has been mature, and the metal sliding isolation bearings is only researched by the developed countries, but it has great development prospects. With the isolation technology used in high-rise buildings,the overturning of the isolation structure is greatly necessary to be researched.The factors to the overturning of the metal bearing isolation are variety, but the most important of which is the height-width ratio of the isolation structure. In order to keep the isolation structure from overturning, there are three stable preconditions. One precondition is that the tensile stress cannot be appeared in the metal isolation bearing at the edge of the isolation story, the other precondition is that the compression stress of the metal isolation bearing at the edge of the isolation story cannot exceed the allowable value, and the last precondition is that the horizontal displacement of the isolation story in the strong earthquake cannot exceed the allowable value. Based on the three preconditions, the horizontal seismic action and the vertical seismic action are considered, then the height-width ratio of the metal isolation structure in the various earthquake fortification intensities could be got. The results show that the height-width ratio of the metal isolation structure is related to the arrangement of the metal isolation bearings, site classifications, the earthquake fortification intensities,the structure ringing period and the damping ratio of the isolation story.According to the formula of the height-width ratio of the metal isolation structure,it can be concluded that the main factor about the height-width ratio is the isolation system period. When it is restricted by the frist precondition, the height-width ratio of the metal isolation structure increases with the isolation system period and decreases when restricted by the second one. So the height-width ratio reaches its maximum valume at a critical period. However, the allowable value of the compression stress of the metal isolation bearing and the horizontal displacement of the isolation story decide the maximum valume of the isolation system period. The height-width ratio should be amended by the critical and maximum period. Generally, in intensity of seldom occurred earthquake of fortification level 7, the isolation system period is restricted by the maximum compression stress of the metal isolation bearing. So the height-width ratio of the metal isolation structure depends on the maximum compression stress of the metal isolation bearing. In intensity of seldom occurred earthquake of fortification level 8 or 9, the isolation system period is restricted by the maximum horizontal displacement of the isolation story. So the height-width ratio of the metal isolation structure depends on the maximum horizontal displacement of the isolation story.From the height-width ratio of the metal isolation structure in various intensity of seldom occurred earthquake, it is found that the amplitude value drops fast when the level is from 7to 8. It is primarily because that the main factor to the height-width ratio has changed. Only depends on itself damping, in intensity of seldom occurred earthquake of fortification level 8 or 9, the horizontal displacement of the isolation story is large. It will affect the height-width ratio at last. So it should exert suitable damping to limit the horizontal displacement of the isolation story, then the height-width ratio of the metal isolation structure can be increased.Finally, SAP2000 is used to simulate the overturning of the metal isolation structure. According to various index, the critical overturning of the metal isolation structure can be found, then the height-width ratio could be easily got. In comparison of the simulated results with the theoretical value, it is found that they fit well and the conclusion is confirmed.