Research On The Dynamic Response And The Vibration Control Of Mega-sub Isolation Structure Under Near-field Earthquake

The mega-sub seismic structure(here in after referred to as the seismic structure)is based on mega frame structure,in which the sub structure is separated from the main structure at the beam-end round sub structure and the top column of sub structure.The mega-sub isolated structure(here in after referred to as the isolated structure)is based on the seismic structure,in which the isolation bearing is arranged at the bottom of each sub structure.The research objects of this paper are the seismic structure and isolated structure,and the main contents of this paper are as follows:(1)Modal analysis and dynamic analysis under near-field earthquake of the seismic structure and isolated structure are carried out by using ETABS finite element analysis software.Simulation results show that setting isolation bearings under the sub structure is different from base isolation in the respect of isolation form and cushion mechanism;low order natural periods of the isolated structure have increased certainly compared with the seismic structure,but high order natural periods of the two structures have less difference;the vibration modes of the two structures are very different;the displacement and acceleration reactions of main frame and sub frame of the isolated structure under near-field earthquake are smaller than that of the seismic structure.Dynamic responses of the isolated structure under near-field earthquake are somewhat larger than that under far-field earthquake.(2)Through shaking table tests of the seismic structure and the isolated structure models with 1:30 reduced scale,structure vibration characteristics and dynamic responses of the two models are studied.Experiment results show that the basic vibration period of the isolated structure has increased slightly,compared with the seismic structure.The isolated sub structure has a tuned mass effect on the main structure.The dynamic responses of the sub structure are reduced evidently after it is being isolated.Under near-field earthquake,the controlled effects of the main structure of the isolated structure are 25%?40%;the controlled effects of the sub structure of the isolated structure are 50%?70%.The dynamic responses of the two structures under near-field earthquake are bigger than that under far-field earthquake.Comparisons between the numerical analysis results and the test results of the vibration characteristics and dynamic responses of the two structures show that the numerical analysis results coincide well with the measured values.(3)The collision between main structure and sub structure in the mega-sub isolated structure is simulated by using ETABS finite element analysis software,and dynamic responses of isolated structure under collision condition are studied.The mega-sub isolated structure model with viscous dampers is systematically analyzed.Simulation results show that acceleration responses of sub structure and main structure under collision condition has dramatically increased compared with the response under no collision condition,which has extremely disadvantageous influence on security of the isolated structure.The way that the viscous damper is set in isolation layer can effectively reduce the displacement of isolation layer,and it has little effect on the tuned mass effect of the sub structure.In the end,the parameters of viscous damper are analyzed.Simulation results show that damping coefficient C can effectively reduce the displacement of isolation layer within a larger scope,which can prevent the mega-sub isolated structure from collision.