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RE: Sg rods at purlins

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Sag rods are used for girts as opposed to purlins.  I would guess from you discription that they are secondary bracing elements for wind uplift when the bottom of the zee purlins go into compression.  Unfortunately, these are generally deterimined directly from testing as opposed to deriving formulas based on testing. That is how the PEMB industry justifies the use of standing seam clips to provide bracing for the compression flanges in the zee purlins for gravity loads. 
Regards, Harold Sprague

> Date: Thu, 13 Nov 2008 15:01:20 -0900
> From: dmorris(--nospam--at)
> To: seaint(--nospam--at)
> Subject: Sg rods at purlins
> I have a question on sag rods. The project that I am working on is a
> pre-manufactured building (unknown manufacturer) with a roof slope of
> 1:12. The 8" deep roof zee purlins span 24 feet and there is an
> L3/4x3/4x 12 gage angle at the midspan that intersects the purlins about
> 5" down from the top. Based on the photos, the angles are not
> continuous from purlin to purlin and seem to be offset vertically, i.e.
> come in different heights on either side of the purlins. We are
> upgrading the roof system for higher snow and seismic loads and need to
> infill with new matching purlins to get the spacing down. Do you have
> any idea whether these angles are sag rods? Since the roof panels are
> already inplace, our thinking was that the sag rods could be cut away
> since the new infill purlins could be installed and screwed to the roof
> panels.
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