Vibration Control Of Mega Frame Structure Under Multi-dimensional Earthquake Exitation

Mega frame structure is a new kind of high rise building structure which is composed of the main structure of super large section and the secondary structure of conventional dimension.With the increase of the height of the building,the seismic and wind load of the structure will be increased,and it will become a new trend in the development of mega frame structure that the vibration control be used in the building.The sub-frame is separated from the main frame in the beam-end in the mega-sub seismic structure(here in after referred to as the seismic structure).Based on the seismic structure,the isolation bearing is arranged at the bottom of of the column of each sub-frame to make the sub-frame to be the sub isolated structure with tuned mass effect in the mega-sub isolated structure(here in after referred to as the isolated structure).Under the effect of earthquake,the seismic responses of the sub-frame are reduced due to the isolation bearing,and the responses of the main frame are reduced by the force the sub-frame transmit to the main frame.The isolation structure combines the damping device and the mega-frame structure in order to achieve the effect of vibration control.Aiming at the vibration control of the mega-sub frame structure,the main research contents of this paper are as follows:(1)Modal analysis and dynamic analysis of the mega-sub seismic structure and mega-sub isolated structure are carried out by using Etabs finite element analysis software.From the analyses,we can conclude that each order of natural vibration period of the isolated structure has increased considerably compared with the seismic structure;the displacement of the main frame beam,the acceleration of the main frame beam,the acceleration of each storey of the sub-frame,the story shear force of the main frame and the inter-story displacement of the sub frames and so on of the isolation structure are smaller than that of the seismic structure.(2)Through shaking table tests on three structure models with 1:30 reduced scale,structure vibration characteristics and seismic responses of the three models under single-direction excitation and two-direction excitation are studied.The three model are seismic structure model,lead rubber bearing isolation structure model and thick rubber isolation structure model.The test results show that the natural vibration period of the lead rubber bearing isolation structure and thick rubber isolation structure were extended and the seismic responses of the structure were reduced compared with the seismic structure;the seismic responses of the structure under two-direction excitation were greater than that under single-direction excitation,and the damping effect of the lead rubber bearing isolation structure is slightly better than that of the thick rubber isolation structure.Comparisons between the numerical analysis results and the test results of the vibration characteristics and dynamic responses of the three structures show that the numerical analysis results coincide well with the measured values.(3)Under one horizontal direction excitation and horizontal and vertical coupling excitation,horizontal seismic responses of the substructure-3D-isolated structure(3D isolated structure)were compared to the seismic response.The results show that the vertical ground motion increases the horizontal displacement response of the substructure.Therefore,natural vibration period,acceleration,story shear force,axial force and displacement responses of the seismic structure,3D isolated structure and horizontal isolated structure were compared and analyzed furtherly.Analysis results also show that 3D isolated structure and horizontal isolated structure have good horizontal damping effect,and vertical vibration control effect of 3D isolated structure is far superior to the horizontal isolated structure.