Bending Behavior Analysis And Repair Technology Of The Existing Railway ?-section Beam Under The Environment Of Dry And Wet Alternation

With the extension of service time,under the multiple effects of load and external environment,the railway ?-section reinforced concrete beam are faced with many problems such as concrete material aging,steel corrosion and structure resistance degradation.It is an urgent task to study the bearing capacity and stiffness of the beam under the condition of disease and to explore the bridge repairing and strengthening methods in line with the characteristics of railway operation.Because of the local structural characteristics of the railway ?-section beam,its external environment has an important impact on the durability of the structure.In this paper,we take the reinforced concrete ?-section beam in the line under the jurisdiction of Northwest Railway as the research object,and the alternating dry-wet micro-environment of the bridge as the main line,Considering the influence of steel bar corrosion caused by the alternation of dry and wet,and concrete shedding disease on the bearing capacity of local members of the beam,and the influence of reinforced concrete bond failure disease on the flexural capacity and flexural stiffness of the structure when there is a failure of bond at the bottom of the beam,At the same time,Considering the feasibility of running heavy haul railway.Finally,putting forward a repair method of concrete shedding disease of railway bridge according to the characteristics of railway operation.The specific contents of this paper are as follows:(1)Based on the inspection of bridges in the railway line of Northwest China,summarized the common diseases of ?-section beam of railway,analyzed the causes of the disease;especially analyzed the corrosion mechanism of steel bars in the environment of alternation of dry and wet conditions;Used the steel bar corrosion rate detector to detecte the corrosion rate of the bridge walking plate in the dry environment and the alternation of dry and wet environment.Verifying the accelerated effect of dry-wet alternating environment on the corrosion of steel bars in concrete structures by the experimental data.(2)According to the current specification,analyzed the bearing capacity of the external cantilever plate of ?-section beam and the barricade which are easy to be affected by the alternation of dry and wet,analyzed the feasibility of passing heavy-duty train.At the same time,checked and calculated the bearing capacity of the outer cantilever plate and the barricade when the concrete shedding disease occurs.Finally,according to the existing calculation result,analyzed the bearing capacity and stiffness of the whole beam with concrete shedding disease.(3)According to the characteristics of railway ?-section beams,maked the corresponding experimental beam model.That is,the tensile bars are reinforced by upper and lower two-story reinforcement.Considering the influence of the local bond failure of the first story tensile steel bar on the bearing capacity and stiffness of the structure;used the finite element numerical simulation method to study the influence on the bending behavior of the structure when the different bond failure lengths and different bond failure positions;(4)Combined with the characteristics of railway bridge operation,this paper puts forward the method of repairing the bridge by using epoxy resin concrete,and on the basis of this,puts forward the optimization repair and strengthening method of adding steel plate as form work and adding steel structure to the bottom of beam.Finally,verified the repair effect by experiment.