Experimental Study On Fatigue Performance Of Existing 8m RC T-girder Of Heavy-haul Railway

With the expansion and reconstruction of the existing railway in China,the train capacity,axle load and traction quality are increasing gradually.The increase of load effect and action times of existing railway bridges has a negative impact on the fatigue performance of reinforced concrete beams with medium and small spans in service,which will affect the traffic safety.In this paper,the 8 m reinforced concrete simply supported T-beam in service with drawing number as special bridge(88)1023 is taken as the research object.The fatigue performance of the full-scale beam under the current operation load and large axle load is systematically studied by the research method of the combination of fatigue performance test and theoretical analysis.At the same time,the adaptability of strengthening technology of fatigue resistance with prestressed CFRP is evaluated.The main contents of this paper are as follows:(1)The stress amplitude of the 8 m reinforced concrete simple supported T-beam under the load of the typical operating train is calculated by the finite element software.Based on the theory of fatigue performance analysis,the fatigue stress cutoff limit and fatigue damage degree are analyzed.The results show that the fatigue stress cut-off limit and fatigue damage degree of the existing T-beams can meet the operation requirements without considering the influence of durability degradation of reinforced concrete members.If the influence of the disease is taken into account when calculating the operating stress amplitude,the corrosion degree of the reinforcement has a great influence on the calculation result of the fatigue damage degree.(2)A total of 12 million fatigue loading tests were carried out on the 8 m reinforced concrete T-beam operated for 20 years.The test load includes the current operation load and large axle load of the railway bridge.In the process of the test,the change rule of the parameters such as the stress of the reinforcement,the deflection of the beam and its natural frequency with the number of fatigue loading is studied.The results show that with the increase of the number of fatigue loading,the deflection and the stress of the main reinforcement of the reinforced concrete T-beam are increasing,the natural frequency is decreasing.At the same time,the length and width of existing cracks and new cracks are developing.The fatigue performance of the in-service 8 m reinforced concrete T-beam under the current railway operation train load is still basically meet the operation requirements,but it is necessary to enhance its fatigue performance through reinforcement if the train load with larger axle load is to be operated.(3)Under the condition of heavy load transportation,prestressed CFRP is used to reinforce the existing 8 m reinforced concrete bridge.The fatigue performance is evaluated by the stress amplitude of reinforced beams.The results show that the fatigue performance of the strengthened beam can meet the traffic requirements under the current operation load and large axle load.