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RE: Truss permanent bracing

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We have talked about this several times in our firm about this topic.  And
finally resolved to state in our General Structural Notes and specs, to
specifically state something to these effects:

THE DESIGN OF ALL WEB MEMBER PERMANENT BRACE SIZES AND CONNECTIONS, REQUIRED
FOR THE STRUCTURAL ADEQUACY OF THE TRUSSES, SHALL BE THE SOLE RESPONSIBILITY
OF THE TRUSS SUPPLIER.
ADDITIONAL MEMBER PERMANENT BRACE SIZES AND CONNECTIONS, NOT PROVIDED BY THE
SHEATHING SHOWN ON THE CONSTRUCTION DRAWINGS, SHALL ALSO BE THE
RESPONSIBILITY OF THE TRUSS SUPPLIER.  THIS BRACING CAN INCLUDE, BUT IS NOT
LIMITED TO, TOP CHORD BRACING FOR TRUSSES WITH PIGGY-BACKS, AND INTERMEDIATE
BRACES FOR GABLE TRUSS WEB MEMBERS.

It is the Truss designer's choice to use a slender member.  If he wants to
use a slender member and brace it so it works, then he should provide the
bracing for it.  So far, we've had no arguments from truss suppliers
regarding this note, and I'll even say I've checked shop drawings that calls
out the bracing for web members.

So that's my 2 cents.

Andy Heigley, PE

Dublin, Ohio

-----Original Message-----
From: Neil Moore [mailto:nmoore(--nospam--at)innercite.com]
Sent: Wednesday, August 17, 2005 1:56 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Truss permanent bracing

Actually, the truss manufacture identifies the web members that have to be
braced for buckling.   He should be giving you the compressive force in
each of these web members.   You, in turn, take some rule of thumb
percentage of that force to determine the required load to resist the
buckling.  From there you multiply this force times the number of trusses
to determine a total load that somehow has to be transferred either to the
building or to the roof or to the gable wall.   Or you add 2x's to each of
the subject web members in the field to eliminate the buckling problem.

This is one of the little gotcha's that is in the TPI code.  The UBC refers
you to the TPI code.

I just noticed that the 2003 IBC requires in section 2304.4.1 item 17 that
the truss shop drawings are to provide the maximum axial compressions
forces "to design the size, connections and anchorage of the permanent
continuous lateral bracing".   The code didn't say who was to design this,
but you will probably find it in the TPI code.

Maybe Charley Truax can fill you in better on this than I have.

Neil Moore, S.E.
neil moore and associates



At 10:28 AM 8/17/2005, you wrote:
>Is it valid to summarize that a simple and rectangular
>single-story hip roof structure with shear wall
>construction would probably not require any "truss
>permanent bracing"?  As I interpret it, the permanent
>bracing is the structural component(s) required to
>transfer loads (generally lateral) from one point in
>the structure to another through the roof trusses.  In
>this case, all lateral load goes directly to the
>diaphragm.
>
>I agree with the argument that in-truss bracing
>required to brace compression members from buckling is
>the responsibility of the truss manufacturer.
>
>An inspector has identified a building design plan as
>deficient because no such bracing is defined.  (The
>project was designed and detailed 100% by the
>architect, but that's another argument.)
>
>Regards,
>Jim Wilson
>
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