Research On Preventive Seismic Strengthening Method Of Existing Railway Gravity Piers

At present,with the rapid development of railway construction,the problem of insufficient seismic capacity have become increasingly prominent due to the lack of seismic fortification or improvement of fortification standards in existing railway bridges.It is very necessary to carry out preventive seismic strengthening of existing bridges with insufficient seismic capacity.The thesis puts forward the preventive seismic strengthening method suitable for railway gravity bridge piers.The basic research is carried out through theoretical analysis,numerical simulation,model test and other means.The research results can provide the basis for the research and engineering application of the seismic strengthening system of railway gravity bridge piers.The main research work of the thesis is as follows:(1)The concept of graded seismic strengthening targets was proposed,and the applicability of preventive seismic strengthening of railway gravity bridge piers was discussed.For the existing railway gravity bridge piers mainly based on bending failure,a method of using steel grid for preventive seismic strengthening is proposed.(2)On the basis of the principle of height determination of steel grid,a pseudo-static test was used to study the failure mode,hysteresis curve,skeleton curve and bearing capacity and stiffness degradation,hysteretic energy dissipation,residual displacement and other main performance indicators of railway gravity bridge piers before and after seismic strengthening under horizontal repeated loading.The influence of the steel grid strengthening thickness(the length of the strengthening horizontal steels),the strengthening height(the length of the strengthening vertical steels)and other parameters on the seismic performance was analyzed,and the strengthening effect was evaluated.Subsequently,the relationship between the test hysteresis curve and the degenerate Clough bilinear model of the railway gravity bridge piers before and after strengthening were compared.(3)The shaking table test was used to study the acceleration response,displacement response,energy dissipation capacity and strain response of strengthening steels of railway gravity bridge piers before and after strengthening.The influence of the strengthening layers on the strengthening effect is analyzed,and the advantages of the layered steel grid in reducing the seismic damage of the pier are expounded.Based on that,the mechanism of the steel grid is made clear by discussing the stress characteristics of the steel grid at different stages.(4)According to the deformation and mechanical mechanism of the steel grid,the primary and secondary steels in the steel grid are identified.The equivalent scheme of steel grid is established,the constitutive relationship of steel grid is proposed,and the calculation formula of elastic stiffness in its constitutive model is given.(5)The simplified multi-spring element model and concentrated plastic hinge model of railway gravity bridge piers before and after strengthening are proposed.The hysteresis relationship of each spring in the simplified multi-spring element model is given,and the approximate calculation formulas of related parameters are proposed.The seismic response of railway gravity bridge piers before and after strengthening is calculated by using nonlinear time history analysis method.(6)The two-stage seismic performance evaluation process and method are proposed.The damage status and damage criteria of railway gravity bridge piers are distinguished and defined.An evaluation method for seismic performance of railway gravity bridge piers under frequent earthquakes is proposed.The Pushover method was used to analyze the seismic capacity of railway gravity bridge piers during rare earthquakes.Based on the IDA vulnerability analysis method,the strengthening effect of railway gravity bridge piers under different strengthening parameters was studied,the sensitivity of the strengthening effect to different strengthening parameters was analyzed,and the damage state between vulnerability analysis and shaking table test of railway gravity bridge piers before and after strengthening was compared.