| The design rules in our existing Specification GB50018-2002 are for Q235, Q345 and not prescribe definitely for high strength cold-formed steel for the lack of the experimental and theoretical studies. A total of 30 550MPa high strength steel cold-formed squared axial compression columns with section thickness of 0.6mm were tested between pinned ends over a range of lengths from 400mm to 2160mm. The results of the experiment show that it is much unconservative for the design of compression long columns with high strength of 550Mpa if according to existing Chinese Specification GB50018-2002.Based on the tests, the finite element program ANSYS9.0 is applied to carry out the finite element nonlinear analysis of 550MPa high strength steel cold-formed squared axial compression columns. The FEM models were then verified by the experimental results in terms of ultimate load-carrying capacity, failure modes. The most numerical calculating results agree well with the test data. Hence, some parameters were simulated using ANSYS in order to obtain a complete graph of variation of length. Meanwhile, Proposals of coupling displacement were proposed in order to substitute touching effect in this paper.Based on the tests and the finite element nonlinear analysis, the paper introduced the method of reduced yield point 0.85 f_y and reduced slenderness to account carrying capacity of the columns for the interaction buckling between local and overall buckling. The improved column design of high strength slender sections were proposed in this paper and the proposed method agree well with the test results and the ANSYS results.
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