Research Of Static Behaviors Of Long-Span Steel Box Girder Cable-Stayed Bridge During Construction

The cable-stayed bridges are playing a increasingly important role in modern bridge.Inrecent years,with the maturity of the cable-stayed bridge design theory,the improvement ofconstruction technology and the emergence of the new materials,the span of the cable-stayedbridge becomes longer and longer,and so far it has pasted more than1000meters.As the spanof the cable-stayed bridge increases,the stiffness and stability of structure relativelydecrease.Especially in the construction process,the final structural system of the cable-stayedbridge has not yet formed,so less structural stiffness and larger displacements happen.Due toinfluence of all kinds of factors,the stress states of the cable-stayed bridge is worse duringconstruction.Taking the Xiangshangang highway bridge,on the basis of previous research anddesign of some countries,the thesis carried out the following study on the static behaviors oflong-span steel box girder cable-stayed bridge during construction:Firstly,setting up the finite element mode by the analysis software,based the minimumbending energy method and forward iteration method,the reasonable finished state and initialtension force of cable were determined.Then static linear analysis of the long-span steel boxgirder cable-stayed bridge was carried out with forward analysis method. Through theanalysis we can get the displacement and internal force of the bridge in each constructionstage.The results showed that in the whole construction process,the structure force met therequirements; at completion state of the bridge,stress of girders and towers,cable force andsupport reaction force all met the objectives of the completion state; In the serviceability limitstage, the structure’s stress was safe under the combination for permanent action and highwaygrade I action.Based on geometrical nonlinearity analysis theory and methods of the cable-stayedbridge, comprehensively considering the influence of three geometrical nonlinearityfactors:the cable’s sag effects,combined effects of bending moment and axial force,and thelarge displacement,on construction stress state of long-span steel box girder cable-stayedbridge,this paper used the finite element analysis software to carry out static nonlinearityanalysis of the bridge in construction process.By comparing with the results of the linearanalysis,the geometrical nonlinearity effects of construction stage are obtained.It showed that the geometrical nonlinearity had a great influence on the displacement and the internal forceof structure during the construction process,and the influence become greater while thecantilever length of the main beam increasing;at the maximum single cantilever stage,thegeometrical nonlinearity effects on the displacement and the internal force of structure hadnearly20percent;at completion state of the bridge,the geometrical nonlinearity effects,thatcaused by the secondary dead load,on the mid-span displacement of main girder had10.4percent,so the geometrical nonlinearity can not be ignored.Study on the calculation method of static gust load for cable stayed bridge was made,andthe related calculation parameters of static gust load of the Xiangshangang highway bridgewere given.Then this paper analyzed the static gust wind response of long-span steel boxgirder cable-stayed bridge during construction process,under-3°,0°and3°wind attackangle.The results of analysis indicated that the structure’s stress was safe and the aerostaticstability was good under40.9m/s wind speed,20-year recurrence,during constructionprocess.Then from wind resistance angle,working scope of the temporary pier wasdetermined,and the wind resistance measures of construction process were given.