| After several decades of development,elastomeric bearing isolation technology has been widely used,and has withstood the tests of several actual earthquakes.However,in existing seismic isolation analysis,only the linear and bilinear constitutive models of elastomeric bearings are considered,which are unable to reflect the mechanical characteristics of elastomeric bearings under large shear deformation due to rare earthquakes,which has seriously affected the reliability of the isolation bearing technology in practical application.Therefore,this paper focuses on the mechanical characteristics of elastomeric bearings subjected to large shear deformation,experimental study and finite element analysis have been conducted,and the main contents and results of the research are described below:(1)100% shear strain test,over 300% large deformation shear test and 100% shear strain test after large deformation shear deformation of 2 natural rubber bearings,and 100% shear strain test of 1 lead rubber bearing have been carried out.Experimental hysteretic curves,equvilatent horizontal stiffness and equvilanet damping ratio of 100% shear strain before and after large deformation shear deformation have been obtained.The test results showed that when the natural rubber bearings reach 220%~260% shear strain,the horizontal stiffness begins to increase,and the stiffness hardening phenomenon appears.After 340% and 390% shear strain large deformation shear deformation of natural rubber bearing,the 100% shear strain equivalent horizontal stiffness will decrease by 12% and 19% respectively,and the stiffness degradation phenomenon occurs.(2)Three-dimensional continuum model of elastomeric bearings has been built and the experiment was simulated by the finite element software ABAQUS.The results showed that the hysteretic curve of finite element simulation coincides with the experimental curve.The neo-Hookean model and the 3 order Yoeh model of rubber material are suitable for simulating the 100% shear strain and large deformation shear deformation of elastomeric bearings respectively.The change of the value of the bulk modulus has little influence on the horizontal stiffness but has a great influence on the vertical stiffness.When bearings go through 100% shear strain,the maximum principal tensile stress is 5.37 MPa,the maximum nominal principal strain is 572%.The inner steel shims stress distribution is uneven,basically remain elastic,and plastic strain only occurs in the very few areas around the middle hole edge.(3)390% large shear strain shear deformation test simulation was conducted.The internal rubber stress uneven degree deepens and stress value increases.Most of the inner rubber is principal tensile stress,and its value is less than breaking stress,with no break,and only very small area in the edge of the hole in the middle part of the bearing breaks.At the edge of the hole in the middle part of the bearing of the internal rubber,nominal principal strain exceeds the limit strain of 700%,and the damage area is expanding rapidly with increasing bearing shear deformation.The inner shims' stress uneven degree deepens.Stress value increases,so as the value of plastic strain range and yielding region,which mainly concentrated in the middle of the bearing where bottom and top plate overlap.(4)A base isolated frame structure conforming to the China specifications has been designed.Elastomeric bearings of the structure and its connecting frame have been built by ABAQUS software.The neo-Hookean model and Ogden model of rubber materials have been selected to demonstrate bearings with or without stiffness hardening.Time history analysis has been employed by inputting 6 near field earthquake waves to study the impact of stiffness hardening on the seismic response.The analysis results showed that under near-fault earthquake of 0.4g~0.6g PGA,the stiffness hardening of the isolation rubber bearings under large deformation will reduce the base displacement by 0.2%~16.2%,will increase the acceleration of the top floor of the superstructure by 3.8%~99.7%,and will increase the storey drift of the superstructure with a maximum increase of 124.8%.(5)The variation law of 100% shear strain equivalent horizontal stiffness degradation of elastomeric bearings has been obtained.An analytical model of base isolation structure has been established by SAP2000,and the time history analysis has been carried out by inputting earthquake waves with different peak acceleration to study the affect of stiffness degradation on seismic response.The analysis results showed that after earthquakes of 0.3g~0.6g PGA,the stiffness degradation of rubber bearing after large shear deformation will reduce the roof acceleration of the superstructure by 0.82%~3.58%,reduce the base shear force by 0.35%~3.91%,and will increase base displacement by 3.65%~16.73% under rare earthquakes. |
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