Structural Mechanics Analysis Of Large Span Steel Box Girder During Incremental Launching Construction

Incremental Launching Construction originates from the longitudinal dragging of the steel bridge,the steel box beam incremental launching construction is to assemble the beam body section by section on the embankment behind the abutment,guide beam and the temporary support auxiliary pushing device are used to push longitudinally,so that the beam body is in place through the temporary sliding device at the top of each pier.This method does not affect the traffic under the bridge,with no need for large lifting equipment,no aerial work throughout,which is suitable for the construction of the equal-section bridges with larger lengths per span and urban bridge.Due to the continuous change exist in the structural force form of the bridge span structure during the construction of the jacking method.The force characteristics of steel box girder beam body、 temporary support pier and steel guide beams is difficult to determine.Therefore,related research and analysis are not enough,it is necessary conduct research around the above issues.Based on incremental launching construction of a long-span steel box girder across the highway.In this paper,a finite element model of the steel box girder,temporary support pier,and steel guide beam of the bridge construction process will be established using Midas / Civil and ABAQUS.It is used to study the force characteristics of steel box girder and temporary structure during the construction of the jacking method.Design advice and construction measures will be made based on the results of the study.The main research contents and conclusions are as follows:(1)Using Midas / Civil to establish a finite element model for the whole process of large-span steel box girder incremental launching construction,study the force characteristics and changes of key components of the steel box girder during incremental launching construction and determine the most unfavorable construction conditions during jacking.The analysis shows that during the construction of the steel box girder,attention should be paid to the change of the force on the bottom plate of the steel box girder above the pushing equipment,and local reinforcement should be carried out.During the incremental launching construction process,the position of the temporary supporting pier distribution beam is continuously changed,and the maximum deformation of the structure is major.The stiffness of the distribution beam should be appropriately increased or guaranteed to avoid stress concentration.Since the jacking process is not the ideal uniform straight-line advancement,the change of the jacking force greatly affects the bottom stress and the top displacement of the temporary support pier,monitoring should be strengthened during incremental launching construction 。(2)A finite element model of temporary support pier for long-span steel box girder incremental launching construction was established using Midas / Civil to study the mechanical performance of temporary buttress pier during construction.Analysis of the design parameters of the temporary buttress shows that:The thickness of the temporary support pier’s steel pipe during jacking has a greater impact on the stress of the temporary support pier,the diameter of steel pipe has a greater impact on the displacement of temporary support pier.The stress is concentrated on the bottom of the steel tube.Local ribbing can be used to reduce the stress concentration on the bottom of the steel tube.Steel pipe column can use Φ630×10 mm or Φ720×8 mm section form;With the decrease of the distance between the lateral bracing of the temporary support pier,the stiffness gradually increases,and the stress at the bottom of the steel pipe column gradually decreases.(3)Using ABAQUS establish a finite element model for buckling analysis of incremental launching construction.By comparing the buckling characteristic value of the guide beam during construction,the guide beam strengthening scheme is studied.The analysis shows that the buckling characteristic value of the two-layer transverse stiffener reinforcement scheme is about 62% higher than that of the single-layer reinforcement scheme.Increasing the number of lateral stiffeners has a greater impact on the buckling characteristic value of the guide beam,especially in the upper 1/4 part of the guide beam web,adding transverse stiffeners at the position can ensure the guide beam is in a safe state during the pushing construction.