Sag Rods vs Lateral torsional buckling in perlins ?

[PPoyyyy]

So were using standard 'euro I' shaped hot rolled Steel for purlins ,The Span is 6 meters (~20 feet) and inclined 6 degrees angle.
And we have one engineer that relies on Sag rods, He sais: "The sage rods create a pin support and Halves the length of torsional buckling to (3m)".

-Is this actually true?...If anyone has a documentation on this please share. Thank you for the help!

 

[BAretired]

Sag rods are usually attached at the middle of the web. They keep purlins from sagging during erection but they do not provide significant resistance to lateral torsional buckling. A steel deck, if properly attached, will provide lateral restraint to the top flange but not to the bottom flange.


BA

 

[weab]

Agree with BA. I could only begin to consider this as effective if the sag rod is placed within the top quarter of the member section. Even if I convinced myself of this, it would only be for top flange. Even then, this would only apply if sag rods are placed on both sides of flange assuming that they only work in tension. This is unlikely at purlins at peak and/or eave.

With that said, this doesn't seem like a good idea to me.

 

[Klitor]

Pretty commonly used in my area,everything weab said must be considered. 2 peak purlins are usually rigidly connected w/ evenly spaced hss and eaves purlins are secured with additional diagonal rods grid in longitudinal direction