Study The Effect Of Crack Damage On Stiffness And Carring Capacity Of Long-span Continuous Prestressed Concrete Box Girder Degree

With the continuous development of our transport services, long-span continuousprestressed concrete box girder bridge has been widely used in engineering with its flexibleconstruction methods, stiffness, span, good mechanical properties for structure. But thesurvey found that a significant number of such bridges, all parts of its box girder crackshave appeared in varying degrees in the operation process. The presence of cracks willdirectly affect the bridge’s safety and durability, must to reinforcement and repair it. How-ever, it is impossible to reinforce and repair one by one for the large number of bridges, soscientific evaluatiaon the actual working conditions of the cracking structure to find theproper maintenance program transformation become very important. Currently, the studyon the cracking long-span prestressed girder bridge so seldom, how to accurately judgmentthe actual working conditions of the crack structure still has not been possible to resolve.This paper will rely on the Huang Yan highway Luohe Bridge, analysis the stiffness,carrying capacity and frequency of the structure in the static and dynamic force before andafter the main box girder crack start cracking.Firstly, this paper analyzed the mechanism of box girder cracks, what leads the box beamcrack causes and the classification of the box beam crack, pointing out that the cracks areinevitable. Then established the characteristics of statistical parameters of bottomtransverse cracks by the statistical point of view, transfer the actual crack to the averagecrack in statistical significance and simulation the cracks by directly creating it in thebeams. Secondly, the required unit for finite element analysis, the constitutive relati-onsmodel, the fracture model, the concrete failure criteria were systematically studied toestablish the computational model. Finally, the paper established the models before andafter the structure cracking with the real bridge design data. Analyze the variation of thestructural stress, deflection and frequency with different longitudinal prestressing loss,different crack width, different crack height and different crack numbers to get the red-uction factor of the stiffness，carrying capacity and frequency of the structure with differentcracking state.Analysis showed that:(1) longitudinal prestressing loss has little effect on the structure’sdeflection at the top of the pier, has greater impact on the structure’s deflection at themidspan;(2) longitudinal prestressing loss has effect on the structure’s compressive stressboth at the top of the pier and at the midspan;(3)the unit failure width of bottom transverse cracks are little impact on the structure;(4) the crack height have an impact on the structure,but when the crack height is tiny the effect is also little and will be gradually stabilized inthe end;(5) the effect is greater when the number of cracks are more.