| Previous earthquakes in China shows that short-to-medium span highway bridges might suffer from severe seismic damages due to the uncontrollable sliding of unbonded laminated rubber bearings(ULNRs).A novel high-performance isolation rubber bearing,which can replace the widely used ULNRs,is proposed to improve the seismic performance of short-to-medium span girder bridges.This novel bearing is reinforced with high-strength and flexible steel wire mesh,and is named Unbonded Steel Mesh Reinforced Rubber Bearing(USRB).When deforming laterally,it can display roll-over deformation.Configuration,manufacture,and installation of USRBs are as simple as that of ULNRs.But USRB can provide higher vertical stiffness,larger lateral stable deformation capacity,and lower lateral stiffness.Due to the unusual reinforcement and unique lateral roll-over behavior,USRB is studied theoretically,numerically,and experimentally in this thesis,particularly on its ultimate loading capacity,lateral properties,and isolation effect when impletemented in bridges.The main contents are as follows.(1)Through literature review,this dissertation investigated the damage patterns of past damaged short-to-medium span bridges due to uncontrollable sliding of ULNRs.The pros and cons of existing seismic design methods and isolation bearings were compared.This dissertation then reviewed previous studies on the application of USRBs in short-to-medium span girder bridges,including preliminary design,mechanical properties,and isolation effect of USRBs.Besides,the development of shaking table tests on isolated highway bridges was summarized.(2)Ultimate loading capacity of USRBs under compression was investigated experimentally,theoretically,and numerically.Firstly,a large amount of ultimate loading tests was conducted to explore the failure mechanism of USRBs under compression,and to statistically evaluate the ultimate loading capacity of USRBs.Then,theoretical analysis was performed to get a closeform solution of the stress in the steel mesh reinforcement,which determines the ultimate loading capacity of USRBs.Stress distribution in the reinforcement and its influencing factors were discussed.Furthermore,finite element analysis of USRBs under compression was performed to explore the ultimate stress state of USRBs.Sensitivity analysis was carried out to investigate the influences of various factors on ultimate loading capacity of USRBs,from which a regressed formula was proposed for the estimation of ultimate loading capacity of USRBs during the preliminary design stage.(3)Lateral responses behavior of USRBs were evaluated experimentally,numerically,and theoretically.Firstly,lateral static and cyclic loading tests were conducted to investigate the lateral deforming process,lateral displacement capacity,lateral stiffness,and hysteretic performance of USRBs.Then,3-D finite element model of USRBs under lateral cyclic loading was established to explore the ultimate stress state of USRBs.Various factors including bearing configuration,material properties,vertical loading and so on,were studied to find their influences on USRBs’ lateral mechanical properties.Moreover,theoretical analysis was performed on the lateral behavior of USRBs.Two restoring force models were proposed for static structural analysis and dynamic structural analysis,separately.(4)Isolation effect and dynamic deforming stability of USRBs were studied by shaking table tests.Firstly,prototype of a two-span continuous girder bridge for the test was determined based on a typical short-to-medium span highway bridge in China.For comparison,the prototype bridge was isolated by USRBs only and ULNRs only,respectively.The prototype bridge has two sets of substructures,one is of the same pier height,and the other is of varying pier heights.Then,detailed information was provided on the similitude design,manufacturing,and installation of the test bridge model.Besides,lateral cyclic loading test results of scaled bearing models,test instrumentation,selection of test motions,and test programs were introduced.(5)Test results and numerical simulation results of the shaking table tests were discussed.Firstly,structural responses of all test programs were listed in detail.Then,comparisons of different test programs were made to study some key issues of USRB-isolated bridge,such as the soundness of replacing ULNRs in reducing span unseating and bearing sliding damage,influence of pier height on structural dynamic response and bearing performance,influence of earthquake characteristics on bearing isolation performance,directional correlation of USRBs,failure mode of USRBs isolated bridge under strong ground motions.A numerical test bridge model was established and got verified by comparison with the test results,where the bilinear restoring force model of USRB was obtained from its backbone curve.Then,this method was applied in the seismic analysis of a continuous girder bridge isolated by USRBs and ULNRs,separately.Pier bottom force and bearing sliding displacement of two isolation technology were compared to illustrate the soundness of applying USRB in increasing isolation efficiency and reducing bearing unseating risk.The comprehensive study demonstrates that the USRB is a capable isolation bearing,which can reduce potential damage of span unseating due to uncontrollable bearing sliding for ULNRisolated bridges.USRBs have been demonstrated to be more efficient in isolation,more robust in sustaining various motions,and more reliable in their life-cycle performance.The widespread use of USRBs on highway bridges will thus substantially enhance the seismic resilience of existing transportation infrastructure in China.Due to special constitutes of USRB,the rollover behavior of under strong ground motions shall be further studied.With unbonded conditions,the effect of vertical force also needs investigating.In addition,appropriate restrainer shall be applied in future to guarantee the stability of USRB-isolated bridges in case of the excessive failure of USRBs. |
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