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RE: LG Truss bracing steel beams

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I have used LGS trusses to brace the beam they are bearing on.  The roof was sheathed with plywood providing a load path for the lateral flange brace force and the trusses were at 2’-0” o.c.  The beam flanges weren’t extremely large (I don’t recall what the beam sizes were).  For small W-shapes, the lateral flange force is very small and typical roof truss framing and connections should have no problem resisting this lateral load, though reviewing the truss shop drawings should help to decide if the bottom chord has adequate axial capacity based on size, brace locations, etc.  For larger W-shapes, I would recommend specifying the connection from the truss to the W-beam and providing the lateral flange bracing force to the truss designer.  I would also recommend using an unbraced length adequate to allow 1 or 2 truss connections to “fail”... just an additional factor of safety. 


I have a related question… If I design a beam which requires bracing only at the mid-span, but the actual detail will provide more bracing locations, (such as at 4’ or 5’ o.c.), does each brace have to be designed for 2% of the lateral flange force or can I assume that the brace locations share the load?



Bruce D. Holcomb, P.E., S.E.

Structural Engineer

Butler, Rosenbury & Partners

300 S. Jefferson, Suite 505

Springfield, MO 65806

ph. 417-865-6100

fax 417-865-6102

Architecture, Engineering, Interior Design, Planning & Development

Your Vision.  Our Focus.


-----Original Message-----
From: Jim Wilson [mailto:wilsonengineers(--nospam--at)]
Sent: Thursday, July 08, 2004 9:29 AM
To: seaint(--nospam--at)
Subject: LG Truss bracing steel beams




Is it practical and efficient to use the lower chord of a light gage truss to brace the top flange of a steel supporting member?


To specify this, wouldn't it then be necessary to put the brace force required on the structural drawings for the light gage truss manufacturer to incorporate?  Thinking out loud, the required stiffness of the lower chord would also need to be specified.  If this goes beyond the realm of conventional truss design software, then it might be necessary to provide member selection guidelines to meet these stiffness and force requirements.


TIA for the thoughts,


Jim Wilson, PE

Stroudsburg, PA

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