The Research On Construction Technology Of Asymmetric Section Prestressed Concrete Large Cantilever Capping Beam

In order to alleviate the phenomenon of the increasingly serious traffic congestion, theviaduct is widely applied in the construction of the urban expressway. The urban viaduct isuse to ensure the enough bridge deck width, but also need to set aside enough space underthe bridge, reduce the influence of the bridge road traffic as much as possible, so the bridgepier tend to use large cantilever prestressed capping beam. The intersection of the urbanroad is more, and restricted by the road red line, the spans of viaduct is hard to makeunified. Sections of the road need to use different span and height, types and materials onthe upper structure, such as one city viaduct in the steel box girder and concrete box girderjoint uses the asymmetric large cantilever capping beam, which characteristic is crosssection asymmetric, at the same time on both sides of the upper structure dead load andprestressed tendon layout is asymmetrical too, so the state of stress and deformation in theprocess of that construction is more complex, and the research is less.The thesis is combined with the asymmetric cross section of large cantilever cappingbeam engineering example, according to the actual construction of different constructionprocess using Midas civil software to modeling. For the asymmetric cross section largercantilever capping beam in each construction stage of the stress changes, the horizontal andvertical deformation, tension and frame beam in order to cover the percussive cap beamend parts and the root stress factors, such as the loss of prestress control factors to discuss.The temperature change and the influence of torsion effect of capping beam are analyzed.Finally make the cap beam end parts and root stress monitoring of the measured valuescompare with the model calculation value of Midas civil, verify the reliability of modelcalculation, which used as the guidance of the actual construction. The results show that:1) The stress and deformation of the capping beam cantilever part affected by thetemperature change is small, the central of capping beam, pier and collar beam partsmainly affected by the temperature gradient is bigger, which could be used as a secondaryfactor in the construction process.2) Because of the capping beam section, the upper structure dead load and the asymmetry of the prestressed tendon layout, the capping beam will produce horizontaltorsion, the end ministries in lateral will appear horizontal displacement. Horizontaldisplacement is mainly composed of the prestressed partial load, that value is less than1cm in the engineering examples, which could be preset reverse displacement to correct.3) The order of frame beam have a great effect on the cantilever capping beam rootstress and the end cap beam vertical displacement, the reasonable order is first to erect thesteel box girder, and later to erect the concrete box girder, that could make the cap beamforce uniform, and reduce because of the different weight on both sides of the box girderproduce torsional stress.4) The order of the prestressed tensioning have the most significant on the sequenceof the capping beam cantilever root stress, the end horizontal and vertical displacement andloss of prestress, the engineering example of different tensioning sequence of maximumdisplacement and stress value increase30%and21%respectively. The rational of thetensioning sequence is determined by calculation, when the tension, which the strength ofconcrete and the age should meet the requirements, avoid concrete fracturing, unfavorablefor multiple deadlines or other reasons to adjust tensioning sequence.The contents of research, methods and conclusions of this thesis may providereference for the similar large cantilever capping beam construction, which has certainpractical significance and application value.