Permanent Bracing for Pre-manufactured Wooden Roof Trusses

[Forensic74]

I'm looking at long-span (but under 60' span) pre-manufactured wooden scissor trusses each with a highly loaded 2x compression member (10kip+) that isn't attached to the roof sheathing...it flies across the attic space horizontally.

BCSI B-3 gives prescriptive methods for installing permanent bracing of trusses, but would this necessarily cover highly loaded compression members? ie, at what point does permanent truss bracing need to be designed by hand in lieu of following the prescriptions of BCSI B-3?

Of course, the truss designer is mute on the subject and specifically indicates that permanent bracing is not their problem.

 

[JAE]

They may not design the actual bracing members but they sure do need to tell someone where it is required.
They (the truss designers) are the only persons who know what is needed for their individual truss elements.

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[KootK]

highly loaded 2x compression member (10kip+) that isn't attached to the roof sheathing...it flies across the attic space horizontally.

Is it a piggy back truss scenario? A sketch may be in order.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Forensic74]

My question is not where the bracing is needed on the trusses, but for how strong the bracing needs to be.

It's not a piggy back, but i think they intended to make the chords at the ridge removable for transport purposes....basically, the top chord goes horizontal for 10-feet across the attic.

 

[JedClampett]

It's almost always a good approximation to use 2% of the compression member load to stabilize it. This typically is a small number, so feel free to double or triple it.

 

[XR250]

While on this subject, does anyone add the required bracing load for the all the truss top chords into their diaphragm design? i.e. all trusses buckling the same direction.
I never have, but would it be prudent to add something in? Hopefully not!