Research On Structural Verification Of Common Span Bridge And Stress State Evaluation Of T Beam Inclined Crack Under Heavy-haul Transportation

With the continuous increase of axle load,traction mass and traffic density of heavy-haul railway transport trains in China,the operation performance of existing railway Bridges is poor,leading to different kinds and degrees of bridge diseases,especially the inclined cracks of prestressed reinforced concrete beams are more obvious,and the stress characteristics are relatively complex.Beam cracks affect the bearing capacity and durability of the structure,lead to reduced service life of the bridge,and even threaten the operation safety of the bridge structure.The paper summarizes the influence of heavy load transportation conditions on bridge structure,and expounds the necessity of verifying and evaluating the deterioration of bridge structure.Taking the 32 m prestressed concrete simply supported T-beam bridge of the Datqin Line as the research object,the method of combining finite element simulation analysis and field test is used to explore the stress state verification and evaluation technology applicable to the inclined cracks of the web of common span prestressed concrete simply supported T-beam,so as to provide technical support for the later maintenance.The main research contents are as follows:(1)The deterioration condition of common span Bridges on Daqin Line was investigated on site,and the influence of heavy-haul railway transportation on the disease of each part of the bridge was analyzed.Under the condition of heavy load transportation,the bridge structure not only bears the vertical load of heavy axle load,but also the fatigue effect continues to be at a high level,which leads to the emergence and development of structural deterioration diseases,especially the appearance of inclined cracks in the beam end web,which weakens the shear bearing capacity of the prestressed concrete beam.The continuous development will seriously affect the service life and traffic safety of the bridge.(2)Establish the finite element model of 32 m prestressed concrete simply supported T-beam corresponding to the site,calculate the shear stress and principal tensile stress of the bridge structure under operational load theoretically,and analyze the anti-cracking performance of the beam body.The finite element analysis shows that under normal service condition,the shear stress about 4.0m away from the support is the largest,and the shear stress and principal tensile stress at this position are less than the standard limit value,and the inclined section cracking resistance of the original design beam is good.(3)By systematically sorting out the common verification methods of railway Bridges and their practical applications in the evaluation of damaged Bridges,the common stress state evaluation methods of span bridge structures and T-beam oblique cracks under heavy transportation conditions are discussed.In the case of not affecting the transportation order,the verification and evaluation can be carried out by the combination of theoretical analysis,appearance inspection,non-destructive testing and dynamic load test.Through the above research method,the field verification and evaluation of the bridge structure with disease is carried out,the detection target is clear,the detection data is easy to obtain,and the purpose of the bridge structure disease detection can be achieved.The field measurement results show that the dynamic deflection,dynamic stress,natural vibration frequency and transverse amplitude of the cracked beam are not significantly different from those of normal beams,and all meet the standard limits,indicating that the overall stiffness and mechanical performance of the cracked beam have not been significantly weakened at this stage.The continuous development of cracks may lead to stirrup fracture and loss of bearing capacity of inclined section of beam body,so it is necessary to strengthen observation and strengthen treatment in time.