Friday, March 15, 2013

Lateral-Torsional Buckling in Wide Flange beams, I-joists and similar shapes

Hello all,

Recently, someone mentioned proper bracing of cantilevered members; that the bracing should always be installed on the compression face.  This came up on a project I worked on a few years ago, and when I looked into it I found that bracing the compression face of a cantilever can potentially lead to failures.

The AISC Engineering Journal published a document discussing the relationship between bracing location and lateral-torsional buckling in wide flange sections.
http://www.aisc.org/store/p-1108-lateraltorsional-buckling-of-wide-flange-cantilever-beams-pdf.aspx

As mentioned in the abstract, they determined that tension face bracing of cantilevered wide flange beams is more effective than compression face bracing.

With all of this said, I haven't encountered very many situations where cantilevered members with compression side bracing that do not also have a diaphragm or perpendicular members at the tension face.  It can, however, reduce the construction costs and architectural issues by eliminating the need for bracing at the underside of a large cantilevered roof.

Edit 3/19/2013:

For additional discussion, see
http://www.eng-tips.com/viewthread.cfm?qid=275285
and
http://www.eng-tips.com/viewthread.cfm?qid=212541

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