Study On Damage Analysis For The Prestressed Concrete Bridge Based On Inversion Theory

With the rapid development of transportation industry in our country, the long-span pre-stressed concrete box girder bridge is widely used in railway and highway. In recent years, cracking, deflection and other problem are often found in the long-span pre-stressed concrete box girder in service, which has a direct impact on the safety, usability and durability.The paper makes an intensive study about the degradation of flexural stiffness and the state of the effective prestress for the long span prestressed concrete bridge in service. The paper puts forward the identification method of the flexural stiffness and longitudinal effective prestress of the bridge based on the inversion theory. According to the monitoring deflection of the main section of the bridge in service at different time, the flexural stiffness and the longitudinal effective pre-stress are identified by establishing the inversion program. The result shows the flexural stiffness and the longitudinal effective prestress decrease gradually along with the increase of the time. The loss of the longitudinal prestress of the top plate is minimal and the loss of the longitudinal prestress of the bottom plate of the mid-span is maximal.According to investigation data of the crack for the prestressed concrete bridge in service, the statistical parameters of the cross and diagonal crack are established by statistical methods. the deflection and stress are analyzed under three cases,considering the cross crack,the diagonal crack and all the crack. The result shows the crack will make the deflection of beam increase, the cross crack has a greater influence on the deflection of beam than the diagonal crack. The cross crack has a greater influence on the stress of the bottom plate for the side-span and mid-span. The cross crack has a greater influence on the stress of the top plate for the side-span and mid-span and has least influence on the stress of the top plate for the pie. The diagonal crack has least influence on the stress of the top plate for the side-span and mid-span and has a greater influence on the stress of the top plate for the pier. The diagonal crack has least influence on the stress of the bottom plate for the side-span, mid-span and pier. The analysis also indicates that the cross crack has least influence on the web principal stress. The diagonal crack has a greater influence on the web principal stress.According to the relative strain relationship between steel bar and concrete, the calculation formula of the average crack width was deduced. The crack width of the normal section of the beam is analyzed by applying stepped load.