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Weak axis bending of cold-formed steel members

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List,

I was wondering if anyone could point me in the right direction concerning lateral-torsional buckling and weak axis bending for light gage members.  My case is for weak axis bending of a hat section, but I was also wondering about the general case.  I have the three AISI 2001 manuals and I believe I understand the different strengths that need to be calculated, however, the specification manual section C3.1.2 is for “I-, Z-, C- and other symmetric section flexural members” and not for “U- sections”; however there is a Supplementary Part V Section 2 which does include “U-sections”.  It further states that the provisions of this section do not apply to laterally un-braced compression flanges of otherwise laterally stable sections.  I can’t find anything that specifically states that you do not need to check this limit state, but I vaguely remember from my steel design courses (maybe incorrectly) that this does not occur for weak axis bending in general. 

 

My questions are:

 

1)  Is the limit state for Lateral-Torsional Buckling limited to major axis bending as it is in the AISC LRFD Manual section F1.2?

 

2)  Is weak axis bending considered a laterally stable section and therefore you don’t have lateral-torsional buckling?  For example, a C-section in weak axis bending would not need to use the procedures of C3.1.2 or C3.1.3 (One Flange through-fastened to Deck or Sheathing).

 

3)  The Supplementary Part V Section 2 concerning hat sections has exclusions for 1) roof panels and 2) for a system comprised of flexural members and panels.  Does the 2nd exclusion occur only if you have more than 1 hat and therefore you have a system?

 

Thanks,

Bob

 

Bob Riley, P.E.

Mesiti-Miller Engineering, Inc.
224 Walnut Avenue, Suite B
Santa Cruz, CA  95060
voice: 831.426.3186 x105

fax: 831.426.6607

www.m-me.com