Research On Seismic Performance And Seismic Design Method Of Railway Gravity Piers

The mechanical properties of railway gravity pier are different from those of reinforced concrete pier due to its large section size,large stiffness and low reinforcement ratio.In the code for seismic design of railway engineering,only the seismic design method with reinforcement ratio of more than 0.5% is given,but the seismic design method with reinforcement ratio of less than 0.5% is not specified.Therefore,on the basis of existing research at home and abroad,this paper summarizes the railway problems existing in the seismic research of railway gravity pier.By the experimental study and numerical simulation and theoretical analysis,the seismic response characteristics of railway gravity pier are systematically studied,the numerical analysis model of gravity piers is presented,seismic design method and the method to improve the seismic performance of bridge pier are presented.The main research work and results are as follows:(1)Taking railway gravity pier as the research object,Performance parameters such as hysteretic curve,skeleton curve,stiffness degradation,displacement ductility and the failure characteristics of railway gravity pier under cyclic load under different reinforcement ratio and axial pressure ratio are obtained through quasi-static test.It is found that the failure characteristics of bridge piers with a reinforcement ratio of less than 0.5% are significantly different from those of reinforced concrete piers,and the piers with low reinforcement ratio do not form an obvious plastic hinge area at the bottom of the piers.The existing equivalent plastic hinge length calculation formula cannot be used for railway gravity piers with low reinforcement ratio.Based on the statistical analysis of the test results,a formula for calculating the length of the plastic zone of the railway gravity pier is proposed.(2)Taking the railway gravity pier as the research object,the failure characteristics,the absolute acceleration of the pier top and the relative displacement of the pier top under the earthquake are studied.The results show that the lower the reinforcement ratio of the railway gravity pier,the more obvious the shaking phenomenon under the earthquake.(3)Based on the failure characteristics of piers under quasi-static test and the shaking phenomenon of piers under shaking table test,a four-spring numerical analysis model is proposed on the basis of the analysis model of piers under free swing and considering the restraint effect of longitudinal reinforcement.The analysis results of the four-spring model are compared with the experimental results and the calculation results of the fiber element model,and it is verified that the four-spring model can be used for the seismic calculation of the railway gravity pier.(4)Based on the admissible stress method,a simplified eccentricity checking method is proposed for railway gravity pier under small earthquakes.Considering the influence of the reinforcement ratio,the calculation formula of allowable resultant eccentricity of railway gravity pier is proposed.(5)The ductility checking method of railway gravity pier is proposed,and the allowable displacement ductility coefficient limit of railway gravity pier according to finite ductility under rare earthquake is given.(6)In order to improve the seismic performance of railway gravity piers with low reinforcement ratio,a design method of increasing the number of longitudinal reinforcement at the bottom of the pier is proposed.The calculation formula of the height of the reinforced bar is given.The feasibility of increasing the number of longitudinal reinforcement at the bottom of the pier to improve the seismic performance is verified by quasi-static test.(7)In order to solve the problem of insufficient ductility of railway gravity piers,a design method of adding unbonded area of reinforcement at the bottom of the pier is proposed.The feasibility of the design method is verified by numerical analysis.The ductile seismic performance of gravity piers with less reinforcement can be effectively improved without reducing the horizontal load capacity.