Research On Numerical Analysis And Monitoring And Early Warning Technology Of Frame Bridge Crossing Existing Lines

With the rapid economic development,my country’s transportation infrastructure has become more and more perfect,and the continuous densification of railway and highway networks has led to frequent intersections between the two.At present,the underpass of frame bridges is widely used as an economical and beautiful construction method that does not hinder the operation of existing lines.applied to engineering.In view of the fact that the current research focuses on the disturbance of the soil layer and structure caused by the jacking of the frame bridge,the research on the impact of the excavation and unloading of the frame bridge working pit and the dynamic response of the overhead beam under the dynamic load of the train is not mature,and the existing lines and construction The complex construction environment with simultaneous operation increases the potential safety hazards on site,and it is essential to carry out realtime monitoring and risk assessment and early warning work on site.Therefore,this paper relies on the scientific and technological research and development plan of China Railway Chengdu Bureau Group Co.,Ltd.,through on-site monitoring,finite element simulation numerical calculation,theoretical analysis and comprehensive mathematical model evaluation,etc.The following systematic studies have been carried out on early warning:(1)Aiming at the influence of excavation and unloading of the work pit under the frame bridge passing through the existing line,a numerical simulation model is established to calculate and compare and verify with the on-site monitoring data.According to the influence law of the lateral friction resistance of the structure,the uneven settlement distribution range of the subgrade and the surface and the quantitative relationship between the settlement value and the excavation depth are obtained,and the horizontal displacement of the enclosure structure and the lateral friction resistance of the supporting structure along the vertical direction of the pile body are explored.The distribution and variation rules have certain guiding and reference significance for the site construction and monitoring plan of the frame bridge passing through the existing line.(2)Research on the dynamic response law of the overhead beam under the dynamic load of the train in the construction of the frame bridge under the existing line The stability,vertical dynamic acceleration and dynamic displacement response law of the beam body and track at the beam end and mid-span position,and the spectrum analysis is carried out by Fourier transform.The results show that the maximum vertical dynamic acceleration of the car body is 0.276m/s2 during the process of the train passing through the D24-type beam at a speed limit of 45km/h.All are within the limits of safety regulations,and according to the spectrum analysis,the vibration frequency of the beam body is lower than that of the track,and it is speculated that the vibration frequency of the beam body is more affected by the length of the vehicle and the wheelbase under the model condition,while the distance between the longitudinal fasteners is determined.The effect of the induced load frequency on the rail is more significant.(3)By theoretically analyzing the risk characteristics of the construction of the existing line under the frame bridge,a risk evaluation index system focusing on the construction monitoring content is constructed,and the risk level interval of the singlefactor monitoring and evaluation index is determined.The subjective and objective comprehensive evaluation of the weight method and game theory determines the comprehensive weight of the indicators and integrates the nonlinear fuzzy comprehensive evaluation model to determine the multi-indicator comprehensive risk membership level.Formulate an early-warning mechanism and management control measures combining single-factor indicators and comprehensive evaluation,and develop a corresponding monitoring and early-warning management platform to release early-warning information in real time to feedback on-site construction management,and work together to ensure on-site construction safety.