Light-gage steel trusses

[Schambach]

I'm making a light-gage steel truss out of stud shapes. I'm getting that I need to brace both the top and bottom flange of my compression chords. My top chord top flange of course is braced by my roof decking and I don't have a ceiling to brace the bottom flange of my bottom chord. Is this typically done using a block and strap method (like the bracing of studwalls) or X-bracing between the 24" o.c. trusses like I typically see between purlins on PEMB's?

Thanks.

 

[KootK]

Are you specifically concerned with lateral torsional buckling of compression members sheathed on one side? If so, I think that you only really have two options:

1) Design the chords to span between panel points without intermediate LTB bracing.

2) Block and strap as you've suggested.

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.

 

[Schambach]

Thanks. Any advantage to running X-bracing as opposed to block and strapping?

 

[KootK]

None that I can think of. Trying to cross brace such a shallow member seems a bit sketchy anyhow.

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.

 

[Schambach]

Great. Thanks.

 

[XR250]

FWIW, if you flip every other truss, it makes attaching the blocking much easier as you have the hard side of each chord facing one another. Also, the buckling and torsion loads tend to oppose each other. I stopped designing the metal stud trusses and have switched to specifying the proprietary systems. They work much better. For small jobs, they don't make much sense however.

 

[Schambach]

Great idea! Thanks.