Fatigue Properties Study Of Sectional Steel Box Girder In Corrosive Environment

The steel structure has been widely applied in the practical engineering, but some diseases are found during the operating of the large span steel bridge. At the present, the main diseases are steel box girder corrosion and fatigue cracks. Corrosion and fatigue are the common factors to the steel box girder bridge degradation, and there is a mutual promoting effect between corrosion and fatigue. Now the research on the corrosion fatigue property of steel box girder is less, so this paper designs typical specimen of sectional steel box beam, in a certain loading level and load frequency, the corrosion fatigue property of specimen is studied respectively in no corrosion and in different concentration of corrosion. Finally, the hot spot stress of the specimen is analyzed by establishing a finite element model with body element and shell element. The main research contents are as follows:(1)The experimental phenomenon, crack development and life are studied by basing on the corrosion fatigue test. The fatigue damage location of the four specimens is between girder bridge panel and U rib welds, and on the bridge panel parent metal fracture. Corrosion has effects on the fatigue properties of the specimen, the fatigue performance degradation of specimen SJ3 which is after 3% Na Cl corrosion liquid corrosion is most serious, then the specimen SJ2 which is after 1% Na Cl corrosion liquid corrosion and the specimen SJ4 which is after 5% Na Cl corrosion liquid corrosion, finally specimens SJ1 which is without corrosion;(2)The three stages of fatigue cumulative damage formula is established which is based on the measured specimen of the fatigue residual strain, and the researth method can be used for reference in the fatigue damage analysis;(3)The steel box girder specimens are calculated by two kinds of modeling methods,the one method is a finite element model with body element, and the other is a finite element model with body element and shell element. By comparing the calculation results with the test results, the finite element model with body element and shell element is the optimal modeling method.(4)The hot spot stress of steel box girder specimens are analysed by using the body element and shell element finite model, the hot stress of the weld toe is different by different extrapolation method. Considering the effect of corrosion to the weld hot spot stress, at the load level 25 k N and regardless of the protective coating for steel, the bearing capacity of the specimen can’t meet the engineering requirements after the corrosion in ten years.