Study On Seismic Behavior Of Steel Frame Structures Using Separated Three-dimensional Isolation

Various research has been conducted on base isolations in past years and productive achievements have been obtained.The isolation effects are verified by the research and earthquake experience.However,recent study and investigation after the earthquake shows that the vertical vibration of the earthquake significantly affects the behavior of the structure and non-structure components.The current isolation only works in horizontal direction and cannot protect the structure in vertical direction.Researchers have studied the three-dimensional(3D)isolation.The developed techniques mainly focuse on the combined type 3D isolation which is used at the base.One of the main problems of this kind of isolation is the overturing problem caused because of the 3D isolation.To solve this problem,this study proposes a seprated 3D isolation system.It isolates the horizontal and vertical vibrations using the horizontal isolation at the base and the vertical isolation under the floor slab.The ABAQUS and Matlab software are used for simulations,and a two-story steel frame is used for a shaking table test.Through simulations and shaking table test,the isolation mechanisim of the separated 3D isolation and the isolation effect are studied.The main work and conclusions are as follows:(1)Time history analysis is conducted for the separated 3D isolation of a real structure with finite element method(FEM).Using the EL-Centro,JMA,ChiChi and Tianjin ground motions,the isolation parameters including the stiffeness and damping are studied to compare the structural accleration,displacement and stress.The isolation effect is evaluated by comparing the isolated-structure and fixed-base structure.The simulation results show that the acclereation is reduced by more than 60%.In addition,theoretical analysis is conducted for the separated 3D isolation.The transfer function method is utilized in Matlab to study the effect of isolation stiffness and damping.The results are compared with those from the FEM.(2)A two-story steel frame is designed for the shaking table test.Three different cases are tested including the separated 3D isolation,horizontal isolation and without isolation.The shaking table results show that the separated 3D isolation can effectively reduce the structureal response.Comparing to the fixed-base structure,the acclereation is reduced by 29%-72%.(3)The FEM and test results show that the separated 3D isolation can help reduce the internal forces in the columns and beams,because of the reduction of structural accelerations.Also,it is verified that the overturning movement of the floor is negligible because of the low gravity center of the floor and the reduced floor accelerations.(4)Based on the FEM and test result,the feasibility of applying separated 3D isolations by using different isolation components is analyzed and design suggestions are provided.