On the basis of the hypothetic displacement field, various parameters of the box girder section are concentrated in the structural axis, and the displacement model of the generalized degree of freedom is built based on the mechanical character of the box girder.In this case, three dimensional space structures can be simplified as one dimensional structure, and the element of the thin walled box beam can be obtained.Theories of the element take account of the mechanical character of the thin walled box girder structure based on the basic beam theory, which improved significantly the calculation accuracy of the thin walled box beam structure. In addition, the results of the engineering application based on this paper and space grillage analysis method validate that this theory is exact and simple, and it offers a practical and simple way to solve the analysis problem with complex thin walled structure.
