Research On Control Mechanism And Seismic Reduction Performance Of Inter-story Isolation System

Inter-story isolation system, which isolation device is inserted between two middle stories above the structural base level, is a newly isolated structural form developed from the real application of base isolation structures. Presently, in china, inter-story isolation technology is being inceptive stage and tryout in engineering. There are some real engineering applications of inter-story isolation technology in seismic reduction structures using additional stories and structures with stiffness vertically mutated such as the tower apartment built on a large platform, but the systematic special research on the control mechanism and the seismic reduction performance of inter-story isolation system is still deficient.Compare to base isolation system, the isolation device place is relatively higher in inter-story isolation system. The destruction of isolation layer will probably bring on calamitous result, so the exact research on dynamic reliability of inter-story isolation system is necessity. Meanwhile, with the isolation level elevated, the dynamic characteristic of inter-story isolation system will change, whose seismic response is determined by two main vibration modes. The seismic reduction effect on the substructure below the isolation layer is limited, that the other control devices can be added into inter-story isolation system to improve the holistic seismic resistant performance.In this dissertation, the control mechanism of inter-story isolation system is systematically investigated for various isolation levels. By modeling inter-story isolation system as a simple two degree of freedom model and discussing its frequency characteristics, a procedure to optimally design isolation parameters is put forward based on the minimum base shear criteria. After the random vibration analysis on the nonlinear inter-story isolation system, the effect of some parameters, that are the mass ratio, the ratio of post-yield stiffness to elastic stiffness of isolation layer and the yield displacement of isolation layer, on the maximum lateral drift and the accumulative damage energy of the substructure below the isolation layer is revealed.Based on the energy balance principle, three formulas to predict the seismic response about the total shearing force of isolation layer, the maximum isolation drift and the base shearing force of inter-story isolation system are derived. Through analyzing the distribution and dissipation of the earthquake input energy in inter-story isolation structures, the control mechanism of its own is described. Moreover, in Chapter 4, a concept of design energy spectrum is introduced and some artificial simulated seismic waves which satisfied the energy spectrum of site II as well as had the same phase properties of natural seismic records are fitted. Lastly, the precision of the predicted responses of inter-story isolation system are validated using time history analysis method.Taking a practical engineering example as a background, an analysis model to calculate the seismic random response and to evaluate the dynamic reliability of inter-story isolation system is established in Chapter 5. Compared to the Monte Carlo simulation method, the pseudo excitation method is used in seismic random response calculating. Following the design principles of"two stage design processes, three standard performances"in our country's seismic resistant code and in order to implement performance-based design, the conditional failure probabilities of inter-story isolation system under frequently occurred earthquake and the seldomly occurred earthquake, as well as the whole-life failure probability in the fifty design reference periods, are given out in the calculated example. The effect of main design parameters on the dynamic reliability of inter-story isolation system is discussed by contrasting the original structure without isolation.In Chapter 6, the various passive, active and semi-active control devices are added into inter-story isolation system respectively, to further improve the holistic seismic resistant performance of the system. Considering the nonlinear property of the isolation bearing, a simulation procedure to analysis the performance of the entire hybrid isolation control system is coded based on the general Newmark integration method and the SIMULINK module in Matlab. Through a practical engineering example, the effectiveness in seismic reduction of these newly hybrid inter-story isolation control systems is investigated and compared systematically.Finally, double-layer isolation system, as a new method to control seismic responses of large aspect ratio of high-rise buildings, associated the base-isolation and story-isolation is proposed in Chapter 7. The parameter design methods for linear and non-linear isolation layer are given herein. The double-layers isolation system can further extend the period of structures. In addition, it can also assign the deformation of the traditional base-isolation layer into the two isolation layers of this system, which reduce the probability of causing the vertical tensile stress in bearings and avoid the overturning instability. By setting the location of the middle isolation layer rationally, and separating the building's functional layers homogeneously, the earthquake forces in the structure can be distributed evenly that the bending deformation of the high flexible structure is changed to the shear deformation.