| Distortional buckling of thin-walled cold-formed structure was not mentioned explicit by GB50018-2002 specification. And the ratio of web to flange of lipped channel sections given by GB50018-2002 specification is great than 2 . And further study give a more accurate web to flange ratio of 1.6 and point out if web and flange ratio is great than 1.6,local buckling will be the dominate buckling mode in axial compression column unless the lip is too slim. That is , if the condition above is satisfied distortional buckling will not occur in axial compression column. This method will certainly hinder the design of cold-formed thin-walled structure .Small load eccentricity is unavoidable in practical use and even the condition is satisfied distortional will still happen. To beam-column structure, a formula can calculate distortional buckling load .The validity of the formula was proved. This study will compare the results of FEA and the formula.The formula can only calculate elastic buckling load .It is not a practical load. GB50018-2002 use effective section method to calculate load capacity of cold-form thin-walled structures. But GB50018-2002 specification does not point out explicitly whether or not it is also suit for distortional buckling mode. Direct strength method can calculate distortional buckling of axial compression column and full moment beam. Does this method can be used for beam-column is still unknown .This study validate that it also can be used for distortional buckling beam-column under the condition of distortional buckling load calculated by the above formula.In the problem of how to judge distortional buckling, a good method is use load-axial displacement curve. Another method is use load-strain curve. This study use the method of load-axial curve to judge distortional buckling load, and validate post-buckling strength of distortional buckling is quite low.This study also use an effective solution for preventing channel columns from distortional buckling and further analysis show this solution will also improve the strength of distortional members greatly when the load eccentricity e is relativelylarge(e≥1/2b_w). |
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