Structural Performance Analysis And Control Technology Of Continuous Steel Truss Bridge During Cantilever Construction

Having the advantages of long span,light weight,high strength and fast construction speed,steel truss bridge has made great progress in transportation field.In recent years,due to excess capacity and price fall of domestic steel,steel truss bridge has been widely promoted and applied.For three span continuous steel truss girder bridge,if the construction method that the side span is assembled in scaffold and the middle span is assembled with cantilever installation and closing in mid-span is adopted,the influence on traffic or channel under the bridge would be reduced.Compared with single cantilever installation of steel truss,cantilever construction with closing in mid-span has unique advantages such as effectively reducing the maximum cantilever length in the construction process.The construction technology of cantilever assembly with closing in mid-span is studied.Combined with special engineering project,applying the finite element software,Midas/Civil2013,the process of cantilever construction is simulated to analyze the static performances in the process of construction.Before the steel girder joint,because the structure has been deformed under stress,it is necessary to adjust the displacement of the joint by adjusting the position of the support to achieve the goal of smooth installation of the member.On the state of the maximum cantilever,due to unequal cantilever length on both sides,the steel girder structure internal force state and the reaction force on both sides are not same.The internal force state and deformation of the structure can be adjusted symmetrically in the longitudinal bridge direction by adjusting the elevation of the support.It is shown that the bar maximum stress is often smaller than operating period and the largest cantilever structural stress state is not the worse due to bridge panel and bridge deck pavement of the upper structure dead load proportion is larger.Overall collapse stability of the structure in maximum cantilever and structural buckling stability are checked to ensure the construction safety and using side span bridge panel pressure can effectively resist the overall overturning.Based on unstressed state method,internal force and deformation rules of continuous steel truss bridge applying cantilever construction with closing in mid-span are analyzed.It is shown that the non-stress installation of the joint can be realized by adjusting the position of the support in theory and the support must be return to its original position after the closure,then,the internal force state and deformation of the steel truss bridge are in accordance with over formation state,in other word,the bridge final state of continuous steel truss bridge with cantilever construction is not related to the construction process.In order to make the final bridge line shape of continuous steel truss bridge with cantilever construction meet design requirements,the structure line shape of differentconstruction stages is discussed.It is turned out that based on the principle of unstressed state method,the ultimate bridge line shape of cantilever construction steel truss is dependent on the steel girder fabrication line.The steel girder fabrication line is made up of manufacturing pre-camber and vertical curve,and the steel girder line control is actually the pre-camber setting problem of the steel girder beam.The pre-camber of steel truss girder bridge can be get by changing the length of rod pieces of manufacturing.Applying temperature method,by means of finite element software,the eligible adjustment values of truss structure can be get by equaling adjustment to temperature.In order to meet the requirement that the rod pieces of joints must be installed in non-stress state,the technology of closing in mid-span is studied.Before closure of steel truss girder,it is necessary to place hydraulic jacks in three directions in the pier top to adjust the displacement in different directions,which is applied to meet the technical requirements of closure.The vertical displacement of steel truss girder is affected obviously by the rising and cooling of the whole environment.The longitudinal displacement of steel girder joint can be realized by changing the constraint mode of support alternately under the action of temperature change.Calculation and analysis combined with special engineering example are carried out and the result shows that the continuous steel truss bridge can be successfully combined,jacked by 64.6mm on 14# pier,67.5mm on 15# pier and 41.9mm on 16#pier,with the relative longitudinal displacement of 7.2mm.However,the influence of the construction error on the structure should be taken into account when determining the actual adjustment according to the actual structural displacement.By analyzing the influence of the fall amount of the support on the internal force of the structure and the final closure deviation,the internal force state of the structure is ensured to be basically consistent with the design after the fall of the support.