Analysis On Closure Of Multi-span Continuous Rigid-frame Bridge

Multi-span continuous rigid-frame bridge has been widely used in the westernmountainous areas for its features such as multiple spans, high pier and so on. However,various emergencies usually happen during the construction process. The constructionunits often change the construction scheme according to the integrated condition of theactual situation of the construction site, the construction progress of the T-componentsand construction site conditions. The changed closure schemes of multi-span continuousrigid-frame bridge are unusual, unconventional closure schemes as they arise in order tomatch the construction progress and the conditions of construction site. However,changing the original design scheme will cause to the internal force and deformationproblem of the bridge. It also increases the difficulty of the safety and shape control.Therefore, in this paper according to the engineering background of Taoyuan Bridgewhich is under construction, the unconventional closure scheme of Taoyuan Bridge ismodeled and analyzed using the finite element method.Firstly, an analog calculation of Taoyuan bridge design scheme is carried outobtaining the linearity and stress of the bridges when using conventional closure schemefor providing the analysis reference standard for unconventional closure for multi-spancontinuous rigid-frame bridge. According to the actual situation of Taoyuan Bridge,considering only the unconventional closure of side span, unconventional side spanclosure model is built. By compared with the conventional closure model, theunconventional side span closure effect of continuous rigid frame bridge is analyzed.Calculation shows that:①The influence of unconventional side span closure to pier top displacement isremarkable. Considering the small deformation of pier top as well as uniformdeformation of the pier after the closure, unconventional side span closure is morereasonable comparing with the conventional side span closure;②The unconventional side span closure will influence the normal closure of nextside span which increases the difficulty of side span closure;③The unconventional side span closure has a big influence to bridge linearity. Themaximum difference is up to30.5mm which increases the difficulty of constructioncontrolling of the side span;④If the influence to the linearity can be fully considered during the constructionand before the side span closure, the influence of unconventional side span closure to the next side span closure can be eliminated by strengthened stress, unconventional sidespan closure scheme is available.According to the actual situation of Taoyuan Bridge, considering only theunconventional closing sequence, unconventional sequence closure model is built andcompared with the conventional closure models. The influence of unconventionalclosing sequence to continuous rigid-frame bridge is analyzed. Calculation shows that:①Unconventional sequential closure of right part has a larger influence to thelinearity of continuous rigid-frame bridge. The maximum displacement is up to15mm.②Unconventional sequential closure of left part has a larger influence to thelinearity of mid-span and near pier No.4. The maximum displacement is up to18mm.③The large influence to linearity makes construction control more difficult. As aresult, only if the influence to linearity during construction can be fully considered,unconventional sequence closure scheme is feasible.Finally, combining with the actual situation of Taoyuan Bridge, a finite elementmodel is established considering the unconventional side span closure scheme andunconventional closing sequence. The stress and deformation of Taoyuan Bridge arecalculated. The influence of unconventional closure is compared and analyzed.Calculation shows that:①Unconventional closure of left and right part of Taoyuan bridge greatlyinfluences the linearity of beam, especially the girders of the side span. the maximumdisplacement reached31mm.②The maximum camber position is mainly affected by the closing sequence. Themaximum deflection position is mainly affected by the side span closure scheme andcompletion time of the bridge.③Considering the small deformation of pier top as well as uniform deformation ofthe pier after the closure, unconventional closure scheme (changed closure scheme) ofTaoyuan bridge is more reasonable.④Although unconventional closure of the left and the right part of Taoyuan bridgeaffected stress during the construction process. It is with little impact. The structure isstill with great safety margin. So the unconventional closure scheme (changed closurescheme) is feasible in the structural safety.⑤The impact of the unconventional closure scheme to structural internal force isrelatively small and big to the linearity. So only if the influence to linearity duringconstruction can be fully considered, changed closure scheme of the left and the right part of the bridge is feasible.⑥After the determination of the construction program of main beam, the other construction process should not be easily modified during the construction processes. Otherwise, it will not only affect the structural stress of the whole bridge, but also will affect the bridge linearity.