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Light steel structure because of its light weight, beautiful appearance, easy to manufacture, construction, quality, reliable and fast construction investment recovery, in our country has developed rapidly in recent years. Door frame is mostly composed of variable cross-section components, and components of the web in general is very thin, allows local buckling prior to overall buckling. In order to safe and economic design door frame, need to be in-depth study of internal force, displacement and stability. This paper, by using the finite element method study of variable cross section beam element. To get accuracy does not depend on the division of the cell number of the elastic and geometric stiffness matrix, this paper USES the variable cross-section component geometrical feature points obtained by axial and lateral displacement function. Thus derived can be used for door type just stringing elastic analysis of variable cross section beam element stiffness matrix, and through multiple examples of calculus, and its correctness was verified. This paper developed a set of variable cross section beam element finite element analysis program, the variable cross-section portal rigid frame structure system can be accurately within the static calculation and stability analysis. Using the program, compared with constant cross-section beam element with variable cross section beam element with variable cross-section frame differences within the static calculation and stability analysis.
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