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RE: Wind Girts

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My personal opinion is that for sag rods to brace the interior flange of hot
rolled or cold formed girts it would need to meet the following criteria:
1) Attachment must be close to the flange being brace... Up to individual
engineering judgement as to what close is...  I would "off the cuff" say the
outer 1/3 or 1/4 or the member but within a few inches if deep.

2) Brace must prevent movement (i.e. torsion) of that flange either upward
or downward.  Since this is a sag rod you may need to tie the rods into the
foundation and something near the top like an eave strut.  Other
possibilities could be to double nut the rods and anchor them to the
foundation or eave strut.

Technically to be considered a brace it should restrain lateral movement and
torsional movement.  Good technical references are the papers that Joe Yura
or Jim Fisher published.  I am sure there are other good authors out there
on this subject also but those 2 came to mind.  

Most of them talk about the requirements for strength and stiffness.  With
the stiffness calcs you will find that the more braces you add the stronger
they must be... this in part is due to the attempt to increase the mode of
buckling for the member.

My preference, over sag rods/straps, assuming attachment to a hardwall
system (tilt-up, precast, cast on site, masonry, etc.) is to attach a brace
from the inner flange to the wall itself at a +- 45 degree angle.

If a cold formed girt is attached to a wall panel (speaking of metal but may
apply to wood or other materials) is the use of AISI C3.1.3 and select an
appropriate R factor.  This is mainly based upon testing that suggests that
the panel attached to the outside flange provides some bracing for the
inside flange.  If you use this section pay particular attention to the
exceptions list (+- 12 or 13 if I remember correctly).

Don't forget to calculate deflections also!  They might control over the
stress ratios (or allowable loads if using LRFD).

Hope this quick advice helps,
Greg Effland, P.E.
KC MO

-----Original Message-----
From: Michael Zaitz [mailto:mzaitz(--nospam--at)hgbd.com]
Sent: Thursday, June 14, 2001 1:17 PM
To: Structural Engineers Association
Subject: Wind Girts


Hello all;

Curious as to what the design philosophy is for hot rolled wind girts.
Do sag rods brace the interior flange of the girts (assuming that the
siding does brace the outside face)?  Any good references out there on
this subject?  Finally, how does this compare to light ga steel girts?

Thanks

Mike


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