Seismic Mitigation Performance Of Mega-sub Structure Inter-story Isolation System

This thesis assesses the seismic mitigation performance and failure mode of the mega-sub structure inter-story isolation system using an improved pushover analysis method.Shaking table test of a typical mega-sub structure model was conducted to investigates the seismic response of this inter-story isolation structural system under near-fault ground motions containing velocity pulses.(1)Starting with the base isolation system,this thesis puts forward an improved pushover analysis method of seismically isolated structures by choosing the lateral force loading pattern suitable for the base-isolated structure,in which the formula of equivalent damping ratio in FEMA440 was modified and then introduced elastoplastic response spectrum as demand spectrum.A simplified analysis process and calculation examples are given.The results show that the proposed method is simple and can meet the engineering accuracy.The displacement errors resulting from the proposed pushover analysis method for the seismically isolated structure are between 10% and 26%.This proposed pushover method can better predict the development trend of structural plastic hinges,which is beneficial to the practical engineering application.(2)A typical inter-story isolated structure was used as a numerical example.Both the conventional pushover method and the improved modal pushover method were employed for analysis of the seismic performance of the example,and compared with the dynamic time-history analysis to investigate the applicability and accuracy of the selected pushover method for inter-story isolated structures.Furthermore,an appropriate pushover method is selected for a typical mega-sub structure inter-story isolation system model based on its dynamic characteristics for seismic performance analysis.Results show that the improved modal pushover analysis can better evaluate the displacement response of the overall floor of the isolated structure.The improved modal pushover is used to analyze the mega-sub structure inter-story isolation system and the overall performance of the structure is better.The development process of the hinge determines the yield mechanism of the mega-sub structure inter-story isolation system: the end of the main structure conversion beam?the beam at the bottom of the isolation support?the main structure column the substructure beam.(3)The numerical simulation analysis models for the mega-sub structure inter-story isolation system and its asismic counterpart were established within the environment of MATLAB.Near-Fault ground motion records containing velocity pulses with two different generation mechanisms: forward directivity effect and slippage effect,are used as inputs for the numerical simulation.The effect of the mass ratio of main structure to the substructure on the seismic response of the mega-sub structure inter-story isolation system subjected to velocity pulse ground motion was systematically analyzed.The results show that with the increasing structure mass ratio,the seismic mitigation effect is better,up to 63.48%.The velocity pulse effect will lead to a greater displacement response of the mega-sub structure inter-story isolation system.The effect of the slippage effect on the displacement of the top layer of the main structure is slightly larger than that of the forward direction effect,which is slightly larger by 4.8%.The forward directional effect has a greater impact on the displacement of the isolation layer than the slip effect,with an average of 12.15%.(4)Seismic simulation shaking table tests of the mega-sub structure inter-story isolation system were performed to evaluate its performance under ground motions with different characteristics.Refined finite element model of the tested model was developed by use of SAP2000.The results demonstrate that the isolated substructure decoupling from the main structure is similar to the basic isolation mechanism,meanwhile it works as a tuned mass damper with a large mass ratio in the sense of seismic mitigation of the main structure.The seismic performance of the entire structure can be effectively reduced by 20%-60%.In addition,the near fault effect is obvious for the mega-sub structure inter-story isolation system.The slippage effect increased the displacement of the main structure and the substructure of the mega-sub structure inter-story isolation system by 1.38 and 1.29 times,respectively,while the directional effect increased the displacement of the isolation layer by1.53 times.There is a certain error between the measured and simulated results,but the change trend is similar.