Study On Soft Impact Protection Of Base Isolated Structures Under Strong Earthquakes

Because of its excellent performance in previous earthquakes,seismic isolation has become the most widely used shock absorption technology of structure.Previous earthquakes showed that the seismic intensity exceeding the fortification intensity happens from time to time.The isolated structures can greatly reduce the seismic response of the upper structure and protect the structure under rare earthquakes.However,the first period of this kind of structure is a long period.Under the strong earthquakes exceeding the rare earthquakes,the isolation layer will have a large displacement,which cause damage or even failure of isolation bearing,and cause the overturning and collapse of the upper structure.Therefore,it is necessary to explore new and effective soft impact protection measures,which can limit the displacement of the isolation bearing in a reasonable range,so as to guarantee the safety of the base isolated structures under strong earthquakes.The study of this dissertation mainly focuses on the following aspects:(1)A base isolated structure model considered the nonlinearity of the upper structure is established.The fortification intensity is 8 degree,and 5 natural waves and 2 artificial waves are selected for analysis under rare earthquakes of 8,8.5 and 9 degree.The results show that the displacement of the isolation bearing exceeds the design allowable limit or even the failure limit under strong earthquakes exceeding the rare earthquakes of 8 degree.According to the width of the isolation trench determined by the code,the retaining wall is set up.Under the strong earthquakes,the displacement of the isolation layer will exceed the width of the isolation trench.Isolated structure and retaining wall occur the impact,which causes the adverse effects on the upper structure.Although the impact has limited the displacement of the isolation layer,the acceleration,story drift and story shear force of the upper structure are obviously enlarged,which has an adverse effect on the upper structure.(2)In order to limit the displacement of the isolation layer,systematical tests are conducted to the elastic soft impact protection device,which can provide stiffness.The device is mainly composed of natural rubber bearing,shear key and hollow connecting steel plate.Firstly,the basic performance test under 12MPa and the compressive-shear test under OMPa of liner rubber bearing are carried out.Then,three types of elastic soft impact protective devices are tested for the horizontal mechanical performance,to determine equivalent stiffness of the device and rotation angle of the rubber bearing.The influence and difference of different connection mode of shear key,different material of shear key and the hollow connecting steel plate,and whether the outer surface of the shear key with rubber bush are discussed.The difference of the equivalent stiffness between the elastic soft impact protection device and the bearing parts,which of the bearing parts tested under OMPa,are compared and analyzed.(3)An innovative elastic-plastic soft impact protection device,which can provide the stiffness and damping,is developed.Systematical tests are conducted to the the device.The device is mainly composed of lead rubber bearing,shear key and hollow connecting steel plate.Firstly,the basic performance test under 12MPa and the compressive-shear test under OMPa of lead rubber bearing are carried out.Then,three types of elastic-plastic soft impact protective devices are tested for the horizontal mechanical performance,to determine equivalent stiffness of the device and rotation angle of the rubber bearing.The test results of the post-yield stiffness and yielding force between elastic-plastic soft impact protection device and the bearing parts under OMPa-presesure shear test,are compared and analyzed.(4)Elastic and elastic-plastic soft impact protection devices are respectively set up at the isolation layer of seismic isolation model,which is established in this paper,and the time history analysis under rare earthquakes of 8.5 and 9 degree are carried out.The displacement limiting effect of the isolation layer of the isolation layer of the elastic soft impact protection and elastic-plastic soft impact protection with different mechanical properties and protection distance is compared and analyzed.Then the effects of elastic and elastic-plastic soft impact protection devices on acceleration,story drift and story shear force of the upper structure are comparatively analyzed.