MULLION ALLOWABLE DEFLECTION

SKYLIGHT MULLION ALLOWABLE DEFLECTION LIMITS UNEARTHED AT 307 ANNEX

The 2009 IBC is rather silent relating to specific deflection limits for mullions.  You can start to get a flavor for limits associated with sunroom additions and pattio covers as listed in footnote "h" of table 1604.3 but then you are left hungry for more, with no direction.

So here is the scoop.  We have downloaded a document titled "Maximum Allowable Deflection of Framing Systems for Building Cladding Components at Design Wind Loads" and have placed it at G:\Codes\TIR A-11-04 for all to use.  The document suggests design deflection limits for span "L" (which it denotes as clear span, i.e., length of member between reaction points) of L/175 for spans up to 13'-6". and L/240 +1/4" for spans up to about 40'.  These deflections are only a starting point though as deflections are further restricted to prevent tearing of sealant, etc.  You will have to review the document to fully unearth it's hidden secrets.

Ben

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