Analysis Of Mechanical Performance Of Long-span Railway Nielsen System Continuous Beam Arch Composite Bridge In Construction Stage

As a combined bridge structure,the continuous beam arch composite bridge combines the beam bridge and the arch bridge organically.It has the characteristics of large structural rigidity,reasonable stress,and strong spanning ability.In recent years,it has been widely used in high-speed railway bridges.This article relies on the newly constructed Jingxiong Intercity Railway(41.65+132+41.65)m Nielsen system oblique continuous beam-arch composite bridge as the project,and simulates its construction process to provide reference for the construction control of the bridge.The main research contents and conclusions are as follows:(1)The classification and stress characteristics of beam-arch composite bridges are summarized.The research status of the construction simulation and control of continuous beam-arch composite bridges and the local stress on arch legs are summarized.The related theories of construction control are introduced,including the content,methods and related calculation methods of construction control,etc.(2)The finite element simulation software MIDAS/FEA is used to establish a full bridge simulation model based on solid elements.This paper focuses on the analysis of deformation and stress distribution of the main beam,the deformation of the arch ribs,and the stress distribution of the arch rib steel pipe and concrete in each construction stage,and compares the calculated internal force of the suspension rod with the internal force of the designed suspension rod.The results show that the bending and torsional coupling deformation of the main beam during construction is obvious.The bending and torsional coupling deformation of the main beam is mainly manifested by the vertical displacement difference between the left and right webs,and the vertical displacement of the left and right webs of the main beam is basically antisymmetric;the longitudinal normal stress is unevenly distributed along the transverse direction,and the longitudinal normal stress of the obtuse angle side of the main beam is greater than the acute angle side.The cumulative deflections of the left and right arch ribs is basically antisymmetric about the cross section of the arch ribtop.Arch rib steel pipes and concrete are under compression and have large stress reserves at various construction stages.The negative bending moment is large near the arch foot section,and the positive bending moment is large near the arch top section.(3)By analyzing the local stress of the arch foot in the main construction conditions,the distribution and change law of the local stress of the arch foot during the construction stage are obtained.The results show that the local stress of the arch foot is mainly compressed,and there is a certain stress concentration at the supports,the lateral limit,the section stiffness change,the structural corner,the prestressed anchorage area and other parts,and the construction quality control in these areas should be strengthened.The compressive stress of the actue angle side arch foot is obviously greater than that of the obtuse angle side arch foot.The main tensile stress is greater in the upper and lower edges of the surface where the arch rib is inserted into the joint of the arch foot,the contact point between the steel pipe and the arch foot under the arch rib buried in the arch foot,and the contact between the end of the concrete-filled steel tube on the arch rib and the main beam.The arch rib concrete is affected by the ferrule of the steel pipe,and the stress is relatively uniform,and the compressive stress of the arch rib steel pipe has a large safety reserve.