Bearing Capacity Study Of Corroded Steel Box Girder With Medium Span

Steel box girder was widely applied in medium span bridges in our country for it's well torsional performance, overall performance, fast construction speed and less influence on traffic under construction, but as a result of urban industrial environment pollution and the increase of service time, the steel box girder inevitably appear all sorts of structural damage caused by corrosion and seriously affect the service performance of steel box girder bridge, so it is necessary to study degradation of bearing capacity of medium span steel box girder bridge in service to ensure the safe operation of the bridge.Based on the midium span box girder of Shaoxing bridge, and industrial atmospheric environment is adopted to establish the model of the steel box girder. Then from the perspective of corrosion, real bridge detection and theoretical analysis, material test and numerical analysis method are combined to study the effection of uniform corrosion on the bearing capacity of steel box girder. In this paper, the related work and the main conclusions are as follows:?1? C lassification of steel structure corrosion, Coating degradation and assessment method of steel girder are summarized. Coating degradation include coating pulverization, blister, rust, crack and flake. Further more, according to the coating degradation and evaluation methods Shaoxing G104 national high bridge is detected and evaluated, then maintenance methods is proposed.?2? On the basis of the existing atmosphere uniform corrosion prediction research, the chemical composition of steel and region environment factors are taken into account, and the external and internal corrosion depth prediction formula are obtained as C_?=0.036t^0.762 And C_?=0.049t^0.587.?3? The corroded Q345 q C steel plate is carried on tensile test, and discover that mass loss rate is less than 10%, variation of yield strength and tensile strength are not obvious; in the range of 10%- 15%, decline rate of yield strength and tensile strength were 2.12% and 0.02%; more than 15%, decline rate of yield strength and tensile strength decreased obviously were 6.90% and 4.01%, modulus of elasticity decreased by 2.90%.?4? The model of corroded steel box girder is established after coating degradation, and quantitative analysis of steel corrosion depth is made. Then the finite element software ANSYS Workbench16.0 is adopted to analyze the bearing capacity of the bridge. The result is that maximum stress of the steel box girders for normal operating condition do not reach the yield state, bearing capacity of corroded steel box girder after 100 years, decline rate reached 14.9%.?5? The basic theory of structural reliability is summarized, attenuation model of reliability and time-varying reliability is put forward according to the time variation of the reliability of corroded structure. After coating protection function of steel box girder is failed and according to the reliability index calculated that in 10 years when the corrosion of steel box girder bridge should be carried out to repair.