Research And Application On The Mechanical Performance Of The Precast Segmental U-shaped Continuous Beam

The short-line method is a general segmental prefabricated assembly technology in construction.This method can greatly reduce the construction period and has little impact on the surrounding environment.Consequently,it has been widely used in many bridge engineering in recent years.With the vigorous promotion of rail transit in society,in order to increase the clearance under the bridge and reduce the height of the rail surface,the cross-section of the rail viaduct often chooses a U-shaped beam with an under-bearing thin-walled structure.Considering that different from the conventional highway bridges,the application of the short line method in U-shaped beams is still less.How to carry out construction control is particularly important for the reasonable completion of the bridge.Therefore,this thesis studies the construction control technology of segmental prefabricated U-beam bridge with short line method based on an actual instance in a rail transit project.The spatial girder model was used to analyze the stress distribution and deflection.The solid finite element model of No.0 block was built to study the spatial mechanical behavior.And the BIM technology was used to simulate the construction and intelligent management of the assembly process,anticipation assembling deviation.Finally,the assembly method and the adjustable scheme for the possible deviation in the assembly process were explored.The main research contents are as follows:(1)The two main control methods of designed alignment for segmental U-shaped girders by the short line method are discussed and the solutions for conventional and non-conventional errors in the precast process are explained.The spatial girder model of the bridge is established for this actual project to analyze the stress distribution of the main girders and the pre-chamber of each girder section.The actual size of each girder section is compared with the deviation of the design drawings according to the monitoring of the precast segmental U-shaped girders on site.The results show that the deviation value is basically within 5 mm.(2)The finite element model of No.0 block was established,and the beam section was divided into four different working conditions,including the assembly of No.2 block,the assembly of longest cantilever state,the finished dead state and the service state.The values of axial force,shear force and bending moment at both ends of No.0 block were calculated under the four working conditions.In order to ensure the safety and stability of the structure,the amount of tensile reinforcement at this location should be increased appropriately.(3)Revit was used to establish the continuous rigid bridge girder member and parametrize them.All of the members are coded one by one according to the certain rules,and the software Dynamo was adapted for quickly inputting information,which is convenient for later management and query for the members.Finally,the model and construction plan were imported into Navisworks software separately and the TimeLiner function was used to simulate the construction progress,anticipation assembling deviation.This model can arrange the construction process more reasonably,shorten the construction period and save resources.(4)The mechanical behaviors under different factors were investigated.The sensitive analysis showed that the self-weight had a greater effect on the line of the beam section and a smaller effect on the stress of the beam section.The prestresses tension value had a greater effect on the line and stress of the beam section.when the storage time was less than 60 days,the storage time had a greater effect on the line and stress of the beam.When the storage time was more than 60 days,the effect was greater.Therefore,the optimal storage time is 60 days.(5)The alignment control and adjustment methods in the process of segmental assembly were discussed.The on-site assembly process is completed by the bridge erecting machine,and the adjacent U beam is connected by the shear key by the epoxy resin.In order to control the error,the measurement control shall be carried out immediately after the assembly of each beam,and the deviation shall be corrected in time to avoid the accumulation of deviation.The adjustment methods for the size and type of deviation in the assembly process were put forward.When the deviation is tiny,gasket,temporary prestressing and changing shear key could be adopted.When the deviation is large,it could be adjusted by precast blocks and adding wet joints.Simultaneously,the adjustment formula of angle deviation was theoretically derived.