Long-Span Railway-Cum-Road Continuous Steel Truss Bridge Construction Control Method Research

Continuous truss bridges have a relatively strong competitiveness in railway-cum-road bridges for the advantages of great load capacity,strong spanning ability and flexible spatial layout.Due to the high load level of railway-cum-road bridges and the strict requirement for railway line smoothness,the alignment control during the cantilever construction and precise closure in the midspan have always been the key and difficult points in the construction process of steel truss bridges.In this paper,a long-span steel truss bridge with a main span of 175 m is taken as the engineering background.Taking the cantilever construction process control and closure construction method as the research topic,this paper studies the alignment adjustment and closure method,construction process simulation analysis and the steel truss bridge alignment control in the construction process of the bridge.The main contents of this are shown as follows:(1)This paper reviews the construction control theory and correlational research of long-span bridges,introduces the relevant information of the project background,and explains the necessity of construction control of the continuous truss bridge with both highway and railway.(2)This paper analyzes the mechanical process of the method of lifting and lowering the beam on the top of the pier used in the closure construction of the continuous steel truss bridge.In order to compare the deflection curve of the beam after the rise and fall of the pier top with the deflection curve of the beam under the condition of one-time completion of the bridge,the three span continuous steel truss beam in the actual project is simplified to a three span continuous beam with equal cross section under the uniform load for analysis.The differential equation of the beam deflection under two different conditions is solved by the integral method,and the closed solution of the beam deflection is obtained.Comparing the deflection functions of the two kinds of beams,the results show that they are completely consistent,which proves that the linear effect of one-time bridge can be achieved by using the method of lifting and lowering beams on the top of piers.This result provides a theoretical basis for the popularization and application of the method of lifting and lowering beams on the top of piers.(3)In this paper,the key calculation problem in the application of the method of lifting and lowering beam on the top of Pier-the optimal support seat displacement before and after closure is analyzed theoretically.According to the structural system of the bridge before and after closure,based on the rigid body displacement method and the matrix displacement method,the calculation formula of the optimal bearing displacement before and after the system transformation is derived,and the two goals of accurate closure in the midspan and optimal alignment after the beam falling are realized.(4)CSB and MIDAS / civil are used to establish the plane and spatial construction process simulation models of the railway-cum-road bridge,and the support reaction force,member internal force and stress,member stability,overall stability and linear change in the key construction stage of the bridge are compared and analyzed.The calculation results of CSB and Midas are very close,which indicates the finite element analysis results have high reliability.During the whole construction process,the bridge structure is always in a tight and controllable range,and has a large safety margin.The calculated camber is very close to the measured camber,which achieves the design goal of the bridge;(5)Combined with the finite element calculation and the measured data,the effect of the method is evaluated.The results show that the lifting and falling beam method on the top of pier can effectively adjust the position of the closure mouth,ensure the accurate closure in the middle of the span,and through the construction of the falling beam after the closure,effectively improve the internal force state of the bridge,reduce the stress concentration at the middle pier,improve the quality of the bridge alignment,and ensure the smooth realization of the designed bridge alignment.