Analysis And Study On The Tolerance And Stability Of Combined Support For Cast-in-place Box Girder On The Arch Bridge

With the development of large-span continuous beam bridge,the template support system plays an irreplaceable role in bridge construction.However,templates collapse seriously during the construction because of lacking theory and management,miscalculation and other reasons of template support system.Bailey beam steel pipe column support system is one of template support systems,it has been widely used as construction platform in the construction process of prestressed cast-in-situ box girder.With the increase in height of cast-in-situ box girder,in order to meet the demand of structural-load-carrying capacity,it must increase the section size of steel pipe column which is the main vertical force component in the support system.However,the measure also causes a series of problems,such as increasing the difficulty of construction,wasting resources,increasing the economic burden and so on.So the double-leg latticed steel pipe column support system comes into being as a strong complement of Bailey beam column support.This system achieves the maximum cost saving and guarantees the stress property of structure by increasing links(lacing bar or batten plate)between steel tube columns.With the accession of vertical and horizontal links,the template support system turns into a spatial system.Therefore,it is necessary to make force analysis and stability study of the latticed Bailey beam steel pipe column template support system.This paper takes the approach spans of A high-speed railway across the river bridge project as an engineering example,which has such disadvantages as: high quality requirements,poor and complicated geological conditions,great difficulties in high-bracket erection and removal,many interferences and crossover operations,etc.It mainly introduces the design method and research status of high-bracket at home and abroad,and expounds detailing requirements about each member of the high-bracket in corresponding specification and code,and also discusses the stress calculation of each members and the foundation of steel tubular pile in high-bracket.Aside,it describes the construction methods and precautions of the high-bracket erection,preloading and removal.Furthermore,the force analysis of high-bracket is adopted 3D finite element model built by Midas/Civil for calculation.The analysis results indicate that: the total height and the cantilever height in the upside of the lattice column can make critical contributions to the structural stability;the distance between lace bars can exert few influences on structural stability in a constant total height of lattice column when it range from a certain region,while it will decrease the structural stability with oversize-distance between lace bars;there’s no obvious variation on structural stability when there exist uneven axial force and wind load in its four lattices.In addition,material strength,initial imperfection,structure form and construction factor can also make adverse impacts on the lattice column support.The results not only provide a scientific basis for the construction and design of these double-leg latticed column template support systems,but also provide information and experience for future researchers of similar projects.