Research On Incremental Launching Method And Monitoring Technology Of Small-radius And Large-slope Steel Continuous Box Beam Bridge

Due to the fast development of transportation industry and girding progress of high class road, overpasses are becoming more and more common in our country. Some of those new overpasses are flyovers or ramp bridges, which are mostly curved or sloped, because they are built above existing roads. Meanwhile, incremental launching method are widely employed in construction of those bridges due to its advantages of small obstruction of traffic, low requirements for construction site and so on. Consequently, research on problems in incremental launching method for curved or sloped bridges is necessary.Chongqing Huangjiaowan overpass construction F ramp launching project is a typical small-radius and large-slope steel box beam flyover bridge construction which employs incremental launching method. This paper conducts research on global and local stress characteristics of this kind of bridges and also analyses how small radius and large slopes affects incremental launching and space form of the bridge and how pre-camber of tall beam affects incremental launching. Difficulties and important technologies in monitoring incremental launching of sloped or curved bridge are also studied.Main works and conclusions of this paper includes:â‘ Using analysis model in Midas to analyze and calculatechanges in reaction of supports, vertical deflection and stress of the beam in different phases during launching. Meanwhile, using mixed units method to build a local model of the bridge based on shell unit and then analyzing local stress characteristics and also the safety of construction of the beam during launching. Conclusion is drawn that both curving of the bridge and extending of cantilever section of the bridge have negative effects on local stress characteristics of the beam. Then, using analysis model of temporary supports system to evaluate its safety during launching.â‘¡Analyses of effects of small radius and large slope on incremental launching methods of steel box beam and effects of changing in bridge slope on launching force are conducted. Safety measures of avoiding shift during launching are presented. Effects of curvature radius of steel box beam bridges on their lengthways and crossways stability during launching are also analyzed. Space form of small-radius and large-slope steel box beam bridges sections under different assembling modes are calculated and mechanism of how slope and radius affects space form of beam are also studied. Moreover, design methods of curved and sloped space form are discussed.â‘¢Effects of setting pre-camber to tall beam on incremental launching are analyzed, including effects on launching force, stress characteristics of beam, stress characteristics of temporary pier, uneven contact between beam and slide way, and vertical deflection of beam and so on. Evaluation on those effects and solutions are also presented.â‘£Characteristics and difficulties of monitoring small-radius and large-slope steel continuous box beam bridges are analyzed. New method of testing and evaluating deformation and transverse shift of beams is presented and its application in Huangjiaowan project is also introduced.