Main girder of steel box composite girder with long cantilever arms for single-plane cable stayed bridge

The invention relates to a main girder of a steel box composite girder with long cantilever arms for a single-plane cable stayed bridge. The two sides of a steel box girder in the middle of the main girder are respectively provided with a steel cantilever arm, and the steel box girder and the steel cantilever arms are connected by high strength bolts in bolting and welding modes; and the end part of each steel cantilever arm is provided with a longitudinal side beam, the tops of the steel box girder and the steel cantilever arms are paved with concrete bridge decks or cast-in-situ bridge decks, traffic lanes are arranged on the steel cantilever arms, the steel box girder is in a single-box single-chamber structure or multi-chamber structure, and a steel anchor box is arranged at the anchor point of a stayed cable. By adopting the steel box composite girder with long cantilever arms, the stress problems of the main girder, such as the torsion resistance and the like of the single-plane cable stayed bridge, are solved, and the horizontal dimension of the main girder is reduced; the main girder can be transported to the bridge location to carry out erection and installation, thereby solving the problem that the sectional dimension of the appearance is limited; and because most of the components of the main girder are prefabricated ones, the in-situ workload is reduced, and the construction quality and construction period can be effectively guaranteed. The main girder provided by the invention is specially adapted to the construction conditions in severe cold districts, for example, the main girder is applied to the construction of the Wusu Bridge in HeiXiazi Island of Heilongjiang Province, and achieves a good application effect.