Study On Acid Rain Corrosion Fatigue Of Simulated Prestressed Concrete Beams

At present,China’s total length of high-speed railway in operation is the world’s first,and continues to grow.Among high-speed railway Bridges,prestressed concrete box girder is widely used in high-speed railway Bridges because of its advantages of large section stiffness,good lateral integrity,stable quality,easy construction and good mechanical performance.In the actual project,the service environment of high-speed railway Bridges is complicated,which not only needs to bear the dynamic action of train load,but also needs to face the deterioration of performance caused by natural environment(such as acid rain,high temperature,freeze-thaw,sand,etc.).In order to achieve the goal of century-old operation of high-speed railway,it is necessary to study the durability of high-speed railway Bridges in complex service environment.In this paper,the acid rain environment in Jiangxi province is taken as the background,and the corrosion rate and corrosion site are taken as variables.Through static test,fatigue test and post-fatigue static test on the corroded model beams,the variation law of stress strain,concrete strain,crack expansion,amplitude and stiffness of prestressed concrete beams with loading under different conditions are analyzed.The fatigue life and residual bearing capacity of high iron prestressed concrete beams under the double influence of acid rain corrosion environment and fatigue load are studied,which provides a basis for life prediction of high iron prestressed concrete beams.The main research content of this paper is as follows:(1)According to the principle of geometric similarity,16 scaled model beams were designed and manufactured to simulate 32 m high iron prestressed concrete precast box beams.In addition,the acid rain environment in Jiangxi Province was simulated to accelerate the corrosion of the experimental beam.(2)Through the corrosion static test of 5 scale model beams,the crack development,deflection change,the strain between prestressed reinforcement and ordinary reinforcement,the change law of concrete strain with loading and the overall failure pattern of the test beams are compared,and the influence of reinforcement corrosion rate on the static performance of prestressed concrete beams is analyzed.(3)Through the constant amplitude fatigue loading test of 7 different steel bars and steel strand corrosion test beams,the influence of different corrosion rates and different corrosion materials on the fatigue life of test beams was analyzed,and the variation law of the corrosion fatigue life of prestressed concrete beams with steel bars and steel strand corrosion was revealed.(4)The residual bearing capacity of four scaled model beams after corrosion fatigue was tested to analyze the failure form,the change of deflection,the change law of prestressed reinforcement and ordinary reinforcement strain,and the change law of concrete strain with loading,to study the influence of the residual bearing capacity performance of prestressed concrete beams with different corrosion rates of ordinary reinforcement after fatigue,and to reveal the attenuation law of its bearing capacity.(5)With the change of deflection as the macroscopic mechanical characterization,the fatigue damage degradation law of the test beam was obtained by introducing the stiffness damage variable.The fatigue life prediction model and the residual bearing capacity relationship model were established according to the cumulative damage theory of the stiffness attenuation degradation characterization.The feasibility of the model was verified by comparing the measured data results with the prediction conclusions of the model.