| Portal frame structures are widely used for industrial and civil buildings in recent years. At the same time, tapered members which have appropriate section properties are widely used in that kind of structures. So far as the stability of compression member is concerned, the section should be wide and thin for the proper design. For providing the greater carrying capacity, the section of the tapered columns in portal frame structures should be designed with slender web. That would lead to local bucking of the web, but there is considerable post bucking strength before the member collapse. At present, there are some problems in the research of interactive buckling. It is necessary to research further.This thesis is divided into two sections. The first part, the FEM model of tapered I-section beam-columns with slender web which consider the interactive buckling is built for the large-deflection and elastic-plastic analysis. The model is based on the non-linear finite element method for shell structures and the FEM program of ANSYS. In order to simulate the practical situation, the overall imperfection of the members, the local imperfection of the plate components and the residual stresses are considered. The analysis for the in-plane stability of the members is carried out. The correctness of the FEM model's result including carrying capacity, buckling mode and the stress distribution is proved.The second part, parametric analysis of the member is carried out and FEM results of in-plane ultimate load-carrying capacity will be obtained by changing parameters, including web plate width-thickness ratio, flange with-thickness ratio, tapering ratio, slenderness ratio of column and residual stress etc... The influence of these parameters to the elastic-plastic stability carrying capacity is researched. The results are compared with those of current Chinese Technical Specification for Steel Structure of Light-weight Buildings with Portal Frames (CECS102:2002).
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