Analysis And Study On The Influence Of Permafrost Degradation On The Seismic Performance Of Bridge Piers

In recent years,with the global climate warming,permafrost degradation phenomenon appeared,Along the Qinghai Tibet railway,the frozen soil is highly developed,and it has many seismic belts,the degradation of frozen soil is bound to have an impact on the mechanical properties of railway bridges.In this paper,based on the 32 m simple supported beam bridge of Qinghai Tibet railway,the bridge pile cap pier finite element model is established by using midas Civil,and by the response spectrum method and time history analysis method of the upper limit of permafrost degradation by 1.5m and 5.5m,changes of bridge foundation under earthquake in four different soil conditions of internal force and displacement response,so as to explore the regularity of permafrost degradation effect on the seismic performance of the bridge.(1)By comparing the results of response spectrum and time history analysis,the results obtained by the two methods are consistent,the results of the two methods are in accordance with the standard requirements,which means that the seismic wave selected by the time history analysis method is reasonable.(2)With the degradation of permafrost,the natural vibration period of the first two steps of pier is prolonged,the flexibility of the structure is slightly enhanced,which is beneficial to the seismic performance of the pier and its foundation.However,with the degradation of the permafrost,the deformation of the 1 and the second order vibration modes of the pier is obviously greater than that of the natural frozen.In general,the degradation of permafrost is disadvantageous to the pier.(3)Under the condition of four kinds of frozen soil,the horizontal position of the pile body,the pier top and the ground surface increases with the degradation of permafrost,the results show that the frozen soil is more sensitive to the temperature change,and the effect of the saturated frozen soil on the seismic performance of the bridge is also disadvantageous(4)Under the condition of three kinds of soil(gravel soil,sandy soil and silt soil),the horizontal displacement of the pile,pier top and ground of the bridge increases with the degradation of the permafrost,the horizontal displacement of the pile body,the top of the pier and the ground is the largest under the silt soil condition,and the gravel soil is the smallest.(5)The maximum shear force and bending moment of the bridge pier under the condition of four kinds of frozen soil are increased with the degradation of permafrost;The maximum shear force and bending moment of the bottom of the bridge under three kinds of soil(gravel soil,sandy soil and silt soil)are gradually increased with the degradation of permafrost,which indicates that the degradation of permafrost is bad for the bridge.(6)Based on the analysis of bridge piers with different ice content,the conclusions are consistent with those of homogeneous soil layers,That is,the horizontal displacement of the pile body,the ground floor and the top of the pier increases with the degradation of the upper limit of frozen soil,this is unfavorable to the earthquake resistance of the pier.