The Research Of Different Early Maintenance Methods Of Long-Span Prestressed Concrete Continuous Rigid-Frame Bridge’s Box Girder In The Cantilever Construction Segments

In recent years, the cantilever construction of large-span prestressed concretecontinuous rigid frame bridge has been widely used due to their own unique advantagesin the mountain highway construction. However, due to cement hydration, in the earlyconcrete,there have been temperature deformation and autogenous shrinkagedeformation in the cross-section of a larger size box girder, these variants are subject tocertain constraints to produce large tensile stress, These tensile stress exceeds theconcrete to allow tensile stress giving rise to the early cracks. These early cracks seriousimpact on the life of the box girder, causing great harm to the safe of bridge structure, sowe must take effective measures to reduce the cracks in the concrete at early age. Thesetemperature deformation and autogenous shrinkage deformation of early cracks aremainly caused by the temperature and humidity changes associated with cementhydration volume deformation, temperature and humidity are the key factors affectingthe hydration of cement, Therefore, after the concrete pouring, in order to meet the goodconcrete hardening conditions, to reduce the temperature deformation and autogenousshrinkage of concrete, to prevent the cracking of the concrete surface to improve thedurability of concrete. It should be reasonable conservation to maintain the appropriatetemperature and humidity within a certain time.This paper combines the Chongqing Transportation Research projects of “spanprestressed continuous rigid frame bridge cantilever construction process segmentconservation process”, according to Khatanga Bridge Project, Adopt Midas or civilsoftware number to imitate the law of greatly acrossed path to just reach the varietyregulation of the arm of the box beam temperature field. In searching for a most suitableprotecting method for mountain area of the bridge hanged an arm construction in a rowin response to box beam stomach plank outside side, scaleboard of the dint Solved theproblem to protecting a curing of a box of beam crux in a row. The main researchincludes:①Referred information,concrete box beam has been summarized of presentcondition of the early fissure research and grasped commonly used early maintenancemethods;②Through analysis of peculiarity and scope of application about automatic waterspray mist and spraying sealing compound maintenance method. This paper proposessuit the early concrete maintenance method in the process of continuous rigid frame box girder cantilever construction;③Understanding and grasp concrete temperature field theory knowledge, makeuse of Midas/Civil software, build box beam mound top section period and crosssection period models, choosing the right boundary conditions;Separate analog differentenvironmental temperature, different templates materials and different temperatures intothe mold, concrete box beam vary rule in the distribution of temperature field, obtain tothe benefit of the temperature field of concrete maintenance method. According to theabove conclusion，this paper proposes suit the early concrete maintenance method in theprocess of continuous rigid frame box girder cantilever construction.④Analysising the boundary conditions of the three maintenance methods naturalmaintenance, steel template (enclosed mould stick) with natural maintenance and steeltemplate (enclosed mould stick) with automatic water spray mist maintenance, andselecting the parameters of model calculation access relevant informations.This papersimulates the early temperature changes of the three maintenance methods of box girderfield by the Midas/Civil software, analysis the inside and outside temperaturedifferences of the concrete box girder are key parts, and lastly judges the feasibilitymethod of the early maintenance.⑤Through comparing with the three kinds of maintenance methods of concretebox girders of temperature field analysis research and combining wide cantileverconstruction characteristics, the paper chooses the more suitable early combinatorialmaintenance method of the process of prestressed concrete continuous rigid frame boxgirder bridge cantilever construction.