Research On Calculation Method Of Seismic Response For High Damping Isolation Bridge

With the great development of high-speed railway in the mid-western of China,the construction technology of high-speed railway is facing new challenges.At present,the high-speed railway puts forward higher design requirements for the bridge structure.It's necessary to do the seismic design of the railway bridges with the type of gravity piers,which is facing much more difficult problems at present.Therefore,a simplified analysis method based on the high damping response spectrum is proposed,relying on the project engineering of the large span continuous girder bridge of She-Tang River,and perform statistical analysis of the recorded strong earthquakes in Gansu province.Evaluating the dynamic response of the damping coefficient method and the method of specification recommendation in calculating the accuracy of the equivalent damping ratio of the isolated bridge structure,the following conclusions are drawn:(1)Summarizing the current situation and development trend of isolation technologies in bridge structure.Pointing out the existing problems and putting forward to the future development of the isolation technologies.At the same time,the calculation method of equivalent damping ratio and the research status of high damping response spectrum are reviewed.(2)According to statistics of 54 earthquake records in Gansu province and fitting high damping acceleration,velocity and displacement spectrum with different damping ratios,it can be seen that the spectrum values of the three response spectra is decreasing with the increase of damping ratio.Compared with the response spectrum of 5% damping ratio,the high-damping response spectrum is smoother and the shape of spectrum has changed.For the acceleration response spectrum,the characteristic periods Tg of different damping ratio spectrum are different.The characteristic periods Tg of the acceleration response spectrum increased with the increase of damping ratio.The horizontal and vertical response spectrum of earthquake records have the same regular.(3)According to the existing methods of calculating the equivalent damping ratio,this paper introduces the calculation principle of different calculation methods and summarize the advantages and disadvantages of each calculation method and the applicable conditions.Then,deriving the formulas of the calculation method of the equivalent damping ratio of single degree of freedom system when the liquid viscous damper working together with the double curved spherical isolation bearings(4)A finite element model of isolation bridge is built,and comparing with the precisenonlinear time-history analysis,it is concluded that calculation results of the relative displacement response of the pier girder is more accurate than the response of the internal force of the pier when using the method of the high damping response spectrum,which is closer to the calculation results of nonlinear time-history analysis.When calculating the internal force response of the bottom of the pier,the high damping response spectrum method obviously underestimated the internal force response of the bottom of the adjacent pier.The reason is that the shear bolts of the double curved spherical isolation bearing has cut off under the strong earthquake,and the whole bridge bearings are sliding,and the liquid viscous damper is worked together with the double curved spherical isolation bearings to distribute the seismic load to every pier.The internal force response of the fixed pier is greatly reduced and the internal force response of the adjacent pier is increasing.The high damping response spectrum method ignored the influence of the interaction of the double curved spherical isolation bearing and the viscous damper when calculating the internal force response of the pier.(5)Comparing with difference between high damping response spectrum analysis and nonlinear time-history analysis,the conclusion is that the method of maximum moment of the bottom of the pier and the method of specification recommendation are closer to the actual equivalent damping of the isolated bridges,and the calculation error of internal force response is about 20%,and the calculation error of the relative displacement response of the pier is about 6%.However,the method of shearing force is underestimated the equivalent damping ratio of the isolated bridges.Therefore,when using the dynamic response damping coefficient method to calculate the equivalent damping ratio of isolated bridges,it is recommended to use the method of bending moment.The earthquake-reduction coefficient method is clear in concept,convenient in calculation and suitable for isolated bridges,but the calculation error is relatively large,which can be used as the equivalent damping ratio method of of the isolated bridges in preliminary estimation stage.