Research On Technology Of Walking-type Incremental Launching Based On Rolling Friction Principle In Steel Bridge Construction

In recent years,the jacking construction method is vigorously promoted and applied in the construction of bridges for many cross-line highways and municipal projects because of its small impact on the traffic environment under the new bridge.The traditional drag-and-drop pushing method does not require large equipment,but the push operation is troublesome and may damage the beam.The walking-type incremental launching technology adopts mechanized equipment to overcome the shortcomings of the traditional pushing method,and can realize the modularized automatic pushing installation of the bridge.This paper summarizes the research status of walking-type incremental launching technology of bridge,compares and analyzes the characteristics of existing walking-type incremental launching devices,develops a new walking-type incremental launching device based on rolling friction and studies the working performance in the process of jacking and pushing through the combination of experimental research and simulation calculation.The main thrusting working surface of the equipment replaces sliding friction with rolling friction,which further solves the problems of high sliding friction resistance to be overcome during thrusting and the stagnation caused by alternating dynamic and static frictions,and improves the smoothness of thrusting construction.This paper relies on a project of continuous steel box girder bridge and applies new walking-type incremental launching equipment to the project.The analysis method of walkingtype incremental launching construction in the continuous steel box girder bridge is studied through the simulation calculation of the construction stage,and the specific measures and implementation effects of the stepping jacking construction control of the continuous steel box girder bridge are studied in conjunction with the linear monitoring method.The main work and conclusions of the paper are as follows:(1)Research and development of new walking-type incremental launching equipment: This article introduces the basic structure of the new walking-type incremental launching equipment,and explains the mechanical principle and controlling method of the equipment used in the incremental launching construction of the bridge;(2)Experimental research on the new walking-type incremental launching equipment: This article studies the actual motion state and rolling friction coefficient of the new walking-type incremental launching equipment in the no-load or loaded pushing condition through the slope test and the loading test.The research shows that the equipment undergoes a process from accelerating motion to constant speed motion during pushing.The time of accelerating motion is short but continuous and steady.The research shows that the equipment undergoes a process from accelerating motion to constant speed motion during pushing.The time of accelerating motion is short but continuous and stable.The ratio of the horizontal thrust force to the vertical load under the condition of constant motion speed is the rolling friction coefficient;The friction coefficient is linearly related to the square root of the vertical load,and the value is between0.018 and 0.03 when loading from 0 to 200 tons;the rolling friction coefficient under no-load thrusting conditions is approximately equal to the tangent of the slope angle of the thrusting equipment when it just starts moving;(3)Stress analysis of the new walking-type incremental launching equipment: This paper uses the finite element software ABAQUS to analyze the stress of the new walking-type incremental launching equipment under the action of vertical load and horizontal load.Studies show that under certain vertical loads,the use of large-diameter prestressed tension jacks can increase the area of the pressure plate placed on the top of the jack and improve the vertical bearing capacity of the equipment.The local contact stress of the contact area between the roller and the raceway plate is large,which may exceed the allowable stress of the material,but the plastic deformation causes the contact spot to increase due to the three-dimensional compression of the contact area unit,which will inhibit the contact area material from further yielding;When the hollowness of the roller is in the range of 3% ～ 5%,it can reduce the contact stress and improve the deformation resistance of the roller.(4)Analysis of the construction process of the continuous steel box girder bridge incremental launching: Based on the new walking-type incremental launching equipment and its construction technology,the bridge designing software Midas / Civil is used to study the deformation and the law of internal force change of the continuous steel box girder bridge during the walking-type incremental launching.Studies show that: under the condition that the deformation of the bridge and the internal force are not much different,the assembly platform and the thrust platform can be built on the first and second spans;the maximum vertical deformation occurs at the front end of the steel guide beam under the maximum cantilever state.The maximum tensile or compressive stress appears in the section of the top of the middle pier corresponding to the condition where the number of fulcrums decreases.When the assembly length of the box girder segment reaches the maximum,the support reaction force of main pier is the largest;(5)Research on construction control of continuous steel box girder bridges: Based on the control objectives of bridge construction,this paper studies the control methods applicable to the construction of continuous steel box girder bridges by monitoring the elevation of the box girder.The research shows that by adjusting the initial pier-top elevation,assembly platform elevation,setting the pre-camber and other methods,the route of controlling the steel box girder section assembly and section ejection always falls on the design arc line.When the bridge is finally built,the elevation and deformation of the box girder are consistent with the analysis and calculation results.This paper makes a comprehensive analysis of the working performance of the new walking-type incremental launching equipment during jacking and pushing through the above research,and gives sufficient calculation and control methods for the walking-type incremental launching construction of continuous steel box girder bridge,which lays the foundation for further theoretical research and engineering application of the device.