Research On Seismic Behavior Of Sand Cushion-Base Sliding Composite Isolation Rural Buildings

For most parts of northern China in the high earthquake intensity and cold regions,in order to solve the dual hazard of earthquakes and foundation frost heaving for low-rise rural buildings,a composite isolation system which is composed of base sand cushion and foundation sliding isolation layer is proposed in this paper,this system can also eliminate the unfavorable influence of frost heaving on the low-rise rural buildings.The main research work and conclusions are as follows:(1)Research of sand cushion-base sliding composite isolation system for rural buildings in cold areas with high seismic intensityA new composite isolation system combined base sand cushion and sliding isolation was proposed and the seismic isolation mechanism was analyzed by response spectra theory.Composite insolation system can dissipate earthquake energy and eliminate adverse impact of frost heaving of subsoil by foundation ring beam and sand cushion.(2)Study on the material properties of related components in sand cushion-base sliding composite seismic systemThe material properties and detailing requirements of related components have been researched including sliding isolation layer and base sand cushion.The cracking and sliding condition and slip property of sliding layer with the different formula based on different seismic intensity demands were studied.The shear strength and deformability of bound rubber beams were studied.The demands of the material composition and construction technology of sand cushion were discussed.(3)Experimental study on seismic performance of isolation walls with different sliding layer formulaFour low cyclic loading tests of walls(with no isolation measures,with talcum powder modified mortar sliding layer,with steel ball-modified mortar sliding layer,with graphite powder sliding layer)were completed.The failure shape,energy dissipation capacity,stiffness degradation were compared and analyzed among different walls.The experimental results indicated that the isolation walls have great sliding energy dissipation capacity,the sliding layer with low friction coefficient can change the failure mechanism,the isolation walls are always in the elastic period during the experiment,the stiffness of structures is hardly degenerated,the upper structure is prevented from destruction by horizontal sliding and displacement limit of rubber beams.The sliding ability of three formulas is graphite powder,steel ball-modified mortar and talcum powder modified mortar successively.(4)Shaking table test of isolation structure models and traditional structure modelThe research completed shaking table test with 1/4 scale and two floors model of four types(the composite isolation structure,the sliding isolation structure,the sand cushion isolation structure and traditional aseismic structure)and comparison of the dynamic characteristics,earthquake response characteristics and failure characteristics under different earthquake intensity input.Research shows that the seismic performance of aseismic structure with no structural columns is poor,the seismic performance of isolation structures are better,and the seismic performance of the composite isolation structure is best due to the joint work between sand cushion and sliding layer.(5)Numerical simulation of sand cushion-base sliding composite isolation structureThe ABAQUS software was used for elastoplastic time-history dynamic analysis on four kind structures including traditional aseismic structure,sliding isolation structure,sand cushion isolation structure and composite isolation structure under different earthquake intensity input.The difference of dynamic response characteristics were analyzed,the isolation mechanism of composite isolation structure and the reasonable values of the design parameters of composite isolation structure in different intensity areas had been confirmed.(6)Technology Suggestions for sand cushion-base sliding composite isolation rural buildingsBased on the research results of relevant material performance tests,seismic performance tests of sliding isolation walls,the 1/4 scale model shaking table tests,theoretical analysis and numerical simulation,considering the design and construction requirements of the current national codes to isolating building and replacing basal cushion,the design and construction technical points of sand cushion-base sliding composite isolation rural buildings were put forward in the paper,in order to provide reference in engineering application.The innovation points of this paper are as follows:A composite isolation system is proposed,which is combined base sand cushion and sliding isolation.The three particles dynamic analysis model of system is established and the damping mechanism has been obtained.Through the base sand cushion replacement of frozen soils and the setting foundation ring beam,this system can eliminate the hazards of base soil frost heaving and earthquake at the same time.(2)Three kinds of sliding isolation layers are put forward,such as talcum powder modified mortar,steel ball-modified mortar and graphite powder.The seismic behavior of three kinds of sliding isolation walls is studied by the material characteristic test and low reversed cyclic loading test.According to the characteristics of rural building,the discreteness control countermeasures of materials are put forward.(3)Through theoretical analysis,shaking table test and numerical simulation,the seismic response characteristics and influence factor of the sand cushion-base sliding composite isolation system are studied.The design method and detail structure measures based on the preset isolation rate is put forward.