Research On The Fatigue And Corrosion Fracture Performance Of The Box Girder Bridge's Vertical Prestressed Reinforcement

The cracking problem of the box girder is one of the most common and serious problems in the box girder bridge. There are many reasons for box girder cracking, and the lack of effectiveness of vertical prestress is the main one. At present, the studies on the vertical prestress of the box girder bridge are mainly focused on the prestress loss of vertical prestressed reinforcement, and there are few studies on the fatigue damage and corrosion fracture of the vertical prestressed reinforcement caused by the construction quality. This article studies the effective prestress of vertical prestressed reinforcement and its impact on box girder webs by field tests, and researches the fatigue performance and corrosion fracture performance of the vertical prestressed steel stand. The main contents of this thesis include as follows:(1) Field tests in the effective prestress of vertical prestressed reinforcement and strain capacity of box girder webs have been conducted. The effective prestress of vertical prestressed reinforcement is presented by the test results combined with theory and the impact on tensile stress of the box girder webs exerted by effective stress and grouting of vertical prestressed reinforcement is explored.(2) According to the factors causing the corrosion of steel in concrete, prediction model of vertical prestressed steels on initial corrosion time and prediction model of steel corrosion rate on ordinary atmosphere environment are selected. Meanwhile, through calculating the actual projects, the relationship between the vertical prestressed steel strand corrosion rate and corrosion time limit of LiShui River Bridge provides the basis for the analysis of the fatigue fracture properties and corrosion performance of vertical prestressed reinforcement.(3) Based on the basic theory of fatigue damage, and combined with the practical projects, the fatigue stress spectrum value of the vertical prestressed reinforcement of the Lishui River Bridge, completely grouting and not completely grouting, bearing the load models of BS5400, Euocode, Laman (1996) and 550 vehicles is calculated by finite element model. According to the S-N curves of the prestressed steel strand, and using the criteria of Miner linear cumulative damage, the maximum amplitude value of the vertical prestressed reinforcement under the loads of different specifications is 5.24MPa, far less than the fatigue failure stress amplitude 142MPa (cracked section under 105MPa) of the prestressed steel strand. It is concluded that the vertical prestressed reinforcement will never cause fatigue damage.(4) According to the corrosion rate of the vertical prestressed steel strand when the grouting is not full, two assumptions for the surface corrosion cracks of the prestressed steel strand are adopted: the whole annular crack and steel wire local pit-like crack. The stress intensity factors of these two different surface cracks in different years are calculated, and brittle fracture of vertical prestressed steel strand based on the theory of fracture mechanics is determined. The vertical prestressed steel strand will not fracture under the assumption of the whole annular crack, but it will fracture under the assumption of the steel wire local pit-like crack. The extension of corrosion time of steel strand under the assumption of steel wire local pit-like crack is about 40 years.