Isolated Structure With Super-large Displacement Friction Pendulum Bearing And Its Seismic Performance Subjected To Very-rare Earthquakes

Isolation technology is one of the outstanding research achievements in the field of structural seismic in the past half century,and has been widely used.At present,most isolated buildings are concentrated in areas which has potential earthquake risk.Due to the uncertainty of earthquake occurrence,strength and characteristics,isolated buildings may still suffer from very-rare earthquakes in the design period.Increasing the seismic performance resisting very-rare earthquake can not only realize the increasing seismic demand but also improve the safety reserve of the structure.The research of new isolation methods and design methods,which not only pay little cost,but also realize the seismic performance resisting very-rare earthquake is the direction and main content of this paper.Super-structure with isolation technology can maintain in elastic or slightly elastic-plastic range subjected to rare earthquake.The safety of structural members and non-structural members can be protected effectively and seismic performance of the structure is improved.The current research on seismic performance of isolated structures mainly focuses on design earthquake and rare earthquake,and the research on seismic performance of isolated structures under very-rare earthquake is insufficient.The research shows that the damage of traditional isolated structure under very-rare earthquake is mainly caused by the deformation of isolation bearing.Increasing the deformation capacity of isolation bearing can directly and effectively improve the overall seismic performance of isolated structure.Due to the positive correlation between the horizontal deformation capacity and the stiffness of the traditional rubber bearing,there is a contradiction between improving the deformation capacity of the rubber bearing and improving the isolation effect.The horizontal isolation capacity of traditional friction pendulum bearing can avoid the limitation of vertical bearing capacity and bearing size,and can achieve a more flexible isolation layer.Further research and development is expected to achieve a larger horizontal displacement isolation layer,so as to effectively achieve t seismic performance of isolated structures resisting very-rare earthquake.In order to improve the horizontal displacement capacity of the isolation layer and the safety reserve of the main failure mode "isolation layer failure" of the isolation structure,this paper puts forward the isolated structure system with Super Large Displacement Rotation Friction Pendulum Bearing(SLDRFPB)and Super Large Displacement Tradition Friction Pendulum Bearing(SLDTFPB)respectively.By combining theoretical analysis,numerical simulation and experimental verification,the seismic performance of isolated structure system with SLDFPB resisting very-rare earthquake is studied.The main contents are as follows:1.An isolated structure system with SLDRFPB is proposed,in which the main structure is placed in a super large radius sliding sphere,and super long isolation period and super large sliding displacement are realized.By designing a reasonable friction coefficient to control the sliding and energy consumption of the isolation layer,the isolated structure has seismic performance resisting very-rare earthquake.Based on the whole rotation of the superstructure on the sliding surface and the different direction of the reaction force at each contact position of the sliding surface,the motion equation of SLDRFPB is established.It is concluded that SLDRFPB has some mechanical properties different from the traditional friction pendulum isolation structure: the isolation structure has constant stiffness,high stability and good stability;however,the isolation period and friction force do not directly correspond to the radius and friction coefficient of sliding surface.By defining the equivalent radius and the equivalent friction coefficient of the isolated structure with SLDRFPB,the accurate characterization and calculation of the natural period and friction effect of the isolated structure are realized.Through the seismic performance analysis of isolated structure with SLDRFPB,the results show that the superstructure can still keep elastic under very-rare earthquake.The maximum displacement of the isolation layer is far more than the limit displacement of the traditional friction pendulum bearing,but far less than the limit displacement of SLDRFPB.The residual displacement of the isolation layer does not affect the normal use,so isolated structure with SLDRFPB has seismic performance resisting very-rare earthquake.2.In this paper,an isolation structure system with SLDTFPB is proposed,in which the isolation layer is formed by multiple groups of sliding surface and internal block.The isolation system makes the superstructure keep translational motion,and the isolation layer has large deformation capacity,which can meet the requirements of special isolation buildings for translational function and safety subjected to very-rare earthquakes.The motion equation of the isolated layer is established.The equivalent mass,equivalent friction coefficient,equivalent seismic action and other important parameters corresponding to the dynamic characteristics of the isolated structure are derived.Through numerical simulation,it is verified that the isolated structure with SLDTFPB has seismic performance resisting very-rare earthquake.The results show that the superstructure can keep elastic under very-rare earthquake,and the acceleration does not exceed the requirements of acceleration sensitive components.The displacement of the isolation layer is far less than the limit displacement of SLDTFPB,and the isolation capacity of the isolation layer with residual displacement remains unchanged.The application conditions of SLDRFPB and SLDTFPB are compared. SLDRFPB is suitable for isolation buildings with high safety requirements,small swing of the structure and enough sliding space in the horizontal direction of the isolation layer;SLDTFPB is suitable for the isolation building which does not allow small swing and has enough vertical space in the isolation layer.3.In order to carry out the shaking table test of isolated structre with SLDRFPB and isolated structre with SLDTFPB,a 15 story frame isolated structure with SLDFPB is designed.Considering that the deformation of the isolation structure under the earthquake is mainly as its first mode,the equivalent single degree of freedom isolation structure system test model is proposed,which is made up of rigid frame and rubber bearing to simulate the response of the main vibration mode of the superstructure.The SLDRFPB and SLDTFPB are designed and manufactured,and the scale simulation of the isolation layer is realized.The accuracy of dynamic characteristics of the main structure is verified by the white noise test.Through the test of rare and very-rare earthquake conditions with or without initial displacement,the response of the isolated layer is simulated accurately.It is verified that the isolated layer has enough displacement ability and the superstructure can keep elastic under very-rare earthquake.Compared with the loading conditions with or without initial displacement,the isolation effect of superstructure and the sliding trend are basically unchanged,which shows that the residual displacement of the bearing has little influence on the seismic performance.The friction coefficient and the period of isolated structure are calibrated by experiments.The results of the isolation layer and superstructure are in good agreement with the numerical simulation results.4.For high-rise isolated buildings,isolated structure system with multi-isolation layers which has one isolation layer beside every several layers is proposed.The first few isolation periods of the structure can be far beyond the excellent earthquake period,and the seismic effect of the first few modes of the isolated structure is greatly reduced,thus greatly reducing the seismic action of the main structure separated by blocks and the whole structure.In the isolated structure system with multi-SLDRFPBs,the overturning moment produced by earthquake action is opposite to that of the upper structure,and the structure is more difficult to overturn.Taking 20 story isolated structure with double-SLDFPBs as an example,the seismic performance of isolated structure with double-isolation layers subjected to very-rare earthquake is analyzed.The isolation effect is better than that of the bottom isolation structure system,and the overall anti-overturning ability is twice higher.The shaking table test of isolated structure system with double-SLDRFPBs and double-SLDTFPBs is successfully designed and completed.It is verified that isolation structure with double-isolation layers will not destoryed subjected to very-rare earthquake.The isolation effect of the main structure is good and there is no risk of overturning.