Study On The Force And Prestressed Steel Optimization Of Segmental Support Cast-in-Place For Long-span Prestressed Concrete Continuous Box Beam

At present,the hanging basket cantilever casting method is one of the most important construction methods for long-span prestressed concrete continuous box beam bridges.However,due to the weight coefficient limit of the hanging basket,the length of the beam segments using the hanging basket cantilever construction is short.When it is affected by factors such as construction period,cost and site restrictions,sometimes it is necessary to change the construction plan.Changing the hanging basket cantilever casting to the segmental support cast-in-place can combine the original design beam segments and increase the length of the one-time circulating casting beam segment,thus effectively shortening the construction period.In this thesis,the influence of the construction method on the stress characteristics of the continuous girder bridge is studied.The difference of the force of the main beam under the two construction methods of the segmental support cast-in-place and the cantilever cast-in-place can be studied.The demand ratio of the post-stressed steel bundle and the influence of the removal order of the bracket on the stress of the main beam is analyzed.The main works are as follows:1.Using the finite element analysis with the software “Bridge Doctor”,the calculation model using the hanging basket cantilever construction and segmental support cast-in-place construction is established respectively,and the simulation calculation analysis of the construction process of the two construction schemes is carried out.According to the calculation results,the main beam stress,beam displacement and negative bending moment of the pier top beam are compared and analyzed.2.For the segmental support cast-in-place and hanging basket cantilever cast-inplace continuous beam bridges,during the construction process before the main beam is closed,due to the different structural forms of the main beam and the change of the construction method resulting in the change of construction load.Prestressing tendons optimization is analyzed.Three different steel beam optimization schemes were designed for the roof beam and web bundle of the main beam.The calculation models of the three optimization schemes were established respectively,and the optimization of the prestressed steel bundles was analyzed.3.The influence of the sequence of support removal during the construction of the bracket section on the internal force of the main beam,the displacement deformation and the negative bending moment of the pier top beam section is calculated and analyzed.It is divided into three different disassembly schemes,and the calculation models of these three schemes are respectively established to calculate and analyze its construction process.The results of this thesis show that when the continuous beam bridge designed by cantilever construction has to be changed to segmental support cast-in-place construction method is a better alternative to the construction scheme,which can not only improve the construction efficiency,shorten the construction period,but also reduce the prestressing tendons use.The amount of steel bundles is used to save costs,but special attention needs to be paid to construction monitoring and bridge alignment.