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Exerting prestressing force among steel structure can improve mechanical state of structure, increase the rigidity of the structure, achieve the goal of saving materials, reducing the cost. In recent years, the research work in steel structure with prestressed tendons mainly concentrates on prestressing force steel truss, tension rod, compression bar, etc, but the study work to the application in the engineering of bridge building is less. A prestressed steel girder is regarded as composite structure of girder and tendons through establishing prestressed steel cable of high strength in the steel girder.Firstly, this text set forth the kind, characteristic, domestic and international development overview of the steel structure of prestressing force, introduced briefly the idea of finite element, and explained methods adopted in the model of finite element, which contains surrender criterion of material, strengthen rule of material, the relationship of stress and strain for material, and the foundation and solving of double non-linear finite element equations. Secondly, the finite element models of steel box girder and steel box girder with prestressed tendons were established by applying the finite element software ANSYS and MIDAS/Civil separately, introduced the simulation analysis of the whole loading process, and compared and analysed the calculating value and the experiment value, which proved the finite element model was right. The value of limit load, which was caculated by software ANSYS and MIDAS/Civil, was credible in this text through comparing the limit load of steel box girder and steel box girder with prestressed tendons. And this model is adopted to analyse loading-displacement curve, stress diagram, variation of stress at mid-span, variation of strain at mid-span, the increcement of tensile force of steel tendons, and considered the effect of different non-linear factors on the girder. Finally, factors that could have effect on the deflection at mid-span, the stress of the girder and the increcement of tensile force of steel cables, such as the prestressing force, ratio of span to rise, and the different cable layouts.
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