COMPARISON AND ANALYSIS OF LIPPED CHANNEL FLEXURAL MEMBERS' CAPACITY CALCULATED BY SPECIFICATION NAS 2004 AND GB 50018-2002

A separate check on distortional buckling of cold-formed steel members exists in Direct Strength Design Method(DSM) newly accepted by North American Specification NAS 2004.But no specific design rules for it in Technical Code for Cold-Formed Thin-Walled Steel Structure(GB 50018-2002).A summary of distortional buckling behavior is presented.The calculated method of distortional buckling members is introduced and analyzed.Based on the critical elastic distortional buckling stress calculated by simplified analytical model,the bearing capacities of lipped channel flexural members in appendix of GB 50018-2002 are calculated by DSM;and the calculated results show that the bearing capacity of some lipped channel flexural members is governed by distortional buckling.According to the comparisons of calculated results by DSM with results by GB 50018-2002,the conclusions can be drawn that provisions in GB 50018-2002 are safe but too conservative.So a design suggestion that increases the buckling coefficient of flange to 3.0 is proposed.