Seismic Performance And Fragility Analysis Of Base-isolation Steel Frame Structure Based On Force Analogy Method

Base-isolation structure is different from the traditional seismic structure,which isolates and absorbs seismic energy through the isolation layer,and the earthquake effect on upper structure is reduced greatly and the casualties and economic losses is decreased effectively.For the dynamic analysis of base-isolation structure,The upper structure was usually simplified to a linear elastic model.However,researches showed that the upper structure would enter the plastic under the action of strong earthquake,so it is necessary to consider the nonlinear of upper structure.Force analogy method(FAM)is a variable-displacement nonlinear analysis method,and stiffness matrix remains the same in the calculation process,which could improve the calculation efficiency and ensure the stability for the calculation process.While FAM is applied to the isolation structure,on the one hand,constant initial stiffness matrix is used in the whole operation,so it has a high calculation efficiency.on the other hand,energy analysis of the isolation structure is done on the component level,which could calculate the plastic energy dissipation of isolation bearings and the upper structure's components under the action of earthquake.Based on the above two aspects,the theoretical study and numerical simulation analysis of the isolation structure based on the basic principle of FAM are carried out,and the main research content is:(1)Considering bending and shear effects of rubber isolation bearings at the same time,a macroscopic component computing model for a isolation structure and energy equations of a base-isolated structure based on FAM was established,and the dynamic nonlinear analysis and energy analysis were done for the base-isolated structure,and the calculation results of the plastic dissipation of the isolation bearings and components of the upper structures showed that the upper structure would enter the plastic under the action of severe earthquake;Numerical examples analysis proved the effectiveness of FAM applied to the isolation structure,and the isolation effect of isolation structure was further verified.(2)Isolation steel frame structure design based on performance was done according to the basic principle of FAM.Displacement of isolation layer and the upper structure inter-layer displacement angle were used as the performance goals,and isolation structure design process based on the performance was given.The rationality of performance target selection was proved through the analysis of numerical examples,and A new idea and method for isolation structures design was provided.(3)According to the characteristics of isolation structure,damage indices based on the deformation and plastic energy dissipation of isolation layers were established,and four damage performance status of isolation structures were defined,and vulnerability analysis of base isolation structure based on performance was performed.Firstly,the nonlinear dynamicanalysis of base-isolation structure was done based on FAM,and the displacement response and energy dissipation of the structure under seismic action were got.Then statistical regression analysis for the damage values of two kinds of damage indices was performed,the probability calculation formulas for every damage states of structure were derived,thus structure vulnerability curves based on two kinds of damage indices were got.The comparison of numerical analysis results shows that the damage index based on plastic energy dissipation of isolation layers could be reasonable reaction of isolation structure damage degree.