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Re: Truss permanent bracing

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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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