| The fixed pier of continuous girder bridge will become plastic when subjected to earthquakes and result in large relative displacement between the pier and the girder,leading to unseating of the girder and crushing of concrete at pier bottom.Meanwhile,the supporting strength of the unfixed pier cannot be full used and nearly no seismic forces are bear by the unfixed pier.In this paper,a new isolated design method of the steel restrainer device is proposed for continuous girder bridges.This kind of steel bar restrainer device is installed between the unfixed pier and the girder.The energy dissipation capability and displacement restraint performance of steel restrainer device are applied to dissipate the energy input to the bridge.Thus,the steel bar restrainer device can mitigate the relative displacement between the pier and the girder,disperse the horizontal force to unfixed piers,reduce the seismic force and the plastic deformation of fixed piers and improve the seismic performance of the whole continuous girder bridge.The main research work and conclusions are presented as follows:1.The construction form,installation method and working mechanism of steel bar restrainer device are firstly introduced.Then the design parameters of steel bar restrainer device are studied.The constitutive relationship of steel bar restrainer device,the deformation calculation method in each working stage and the mechanical properties parameters of steel bar restrainer devices are deduced.2.The quasi-static tests for three groups of the steel bar restrainer device were carried out.The hysteretic curves,skeleton curves and low cycle fatigue failure modes of the steel bar restrainer device were obtained.The constittutive relationship of the steel bar restrainer device was established.The stiffness degradation,energy dissipation capacity and energy dissipation stability of the steel bar restrainer device were studied.By calculating the concrete stress at the embedded position of the steel bar restrainer device,the affected range of the reaction force of the steel bar restrainer device in concrete foundation and the optimum installation distance of steel bar restrainer device are studied.3.The equivalent principle of equivalent linearization and seven commonly used methods for calculating equivalent linearization are introduced.The variation of the equivalent period and the equivalent damping ratio calculated by each method are compared;and equivalent linearization formulas of the steel bar restrainer device and the fixed pier are studied.The combined equivalent stiffness and equivalent damping ratio of the steel bar restrainer device and movable pier are studied.A simplified mechanical calculation model of the continuous girder bridge with steel bar restrainer devices is established.The seismic responses of the continuous girder bridge model are calculated by the response spectra.The isolated design method of the continuous girder bridge with steel bar restrainer device are proposed4.The time history analyses of continuous girder bridges with and without steel bar restrainer device are carried out and the results are compared.The results reveal that the steel bar restrainer device can dissipate the energy,restrict the relative displacement between piers and girders,reduce the seismic responses of fixed piers and make full use of unfixed piers.The simplified design method of the continuous girder bridge with steel bar restrainer devices is also applied to calculate the seismic responses,and is in good agreement with the results of time history analyses. |
