Span Continuous Box Girder Cantilever Erection Construction Of Linear Control

Recently, with the rapid growth in the economy of our country, there appears the climax of constructing long span bridges at home, because of the rapid extension and application of the technology of prestressed concrete, as well as the emerge as the times require of many different kinds of advance construction methods of prestressed concrete continuous bridge, the construction schedule of bridge is accelerated and the span of prestressed concrete continuous bridge keeps on rising, the cantilever erection construction method came into being and develop in such background. During the period of construction by the cantilever erection construction method, bridge experiences not only the process of generating girder in the stage of T rigid frame, but also the process of system transformation, so bridge has experienced a great complex stress process, in order to ensure the security of bridge during the whole stage of construction, the stress control and geometry control must be made during the stage of construction of bridge. If the geometry of bridge is not controlled strictly, it will not be in order, there will appear unwarrantable altitude difference at the location of closure section, and that will influence on drilling through the tendon and increase the stretching resistance of the tendon; the cantilever erection construction method has the shortcoming of little adjustability. Therefore, for the continuous beam bridges which adopt the cantilever erection method, the marked elevation of dado must be measured accurately in the stage of prefabricating beams, and the elevation of the geometry of bridge must be calculated correctly. It is important for us to make the theoretical calculation of precamber and deflection and obtain manufacture elevation and construction elevation of each girder segment, according to design drawings, construction management plan and prefabricating geometry, at the same time, in the light of different kinds of calculating parameters.With the increasing of long span prestressed concrete bridge adopting cantilever erection construction method, more and more attention are paid to the correlative geometry control theory and practice of long span continuous box girder. So far, there are many theory and method of how to calculate the precamber of the pretressed concrete continuous beam constructed by canlalever erection method. According to the stress state in different stages, not only the effect of the shrinkage and creep of concrete, pre-tension are all considered in terms of the criterions consider, but also the loss of prestress is also taken into account in this paper. At the same time, the effects of variation in strength of concrete in different stages are taken into account in the computation of shrinkage and creep of concrete. The computing formula for the preamber of bridge is:The computing formula for marked elevation of deck after bridge is constructedcompletely:it — rj I rdesign elevation deck vertical curved elevation J precamberwhere. / —the camber created by the pre-tension deduct from by the loss of prestress; ffX --the deflection created by the self weight( the first dead load); /g2~the deflection created by the second dead load;