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Re: Diaphragm

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As mentioned previously, you could use another metal deck under the standing seam roof. 20 ga 3" N deck (joistsa @ 10' oc) as a single span has an allowable load of 65 psf.

Ashraf, Mohammed (Qatar) wrote:

Gary:
I looked to Bemo Manual and they also say 5 feet spacing. So I will try
to reduce spacing of joists and keep it within limits as you mentioned.
But how can I defend it to the client since it has large cost
implications?. How about providing purlins at a spacing of 5' and
keeping joists at a spacing of 10'. Does it help to keep joist spacing
at 10'?.
The minimum design load is 25 psf. Thanks for your help and regards
Ashraf

-----Original Message-----
From: Gary L. Hodgson and Assoc. [mailto:ghodgson(--nospam--at)bellnet.ca] Sent: Tuesday, May 30, 2006 3:05 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Diaphragm

Ashraf,
I had the same feelings as Daryl when I saw a spacing of 10 ft between joists. Of course, we are used to snow loads, (here in Niagara Falls 39 psf on a flat roof), but I would think you should be designing for a minimum of 20 psf (that is code here in Ontario). This probably covers construction loads, etc. My Butler Manual recommends a spacing of 5 ft for their MR24 standing seam roof, but they don't say why or what are the ramifications of larger spacings. I have
walked on a ss roof with 5'-6" spacing and it was like walking on mush.

The contractor told me to stay over the purlins.
In your case, the flat bar bracing depends on local conditions and abilities of the work forces. Bridging is not bracing; rather it is individual bracing of the joists to stabilize them during construction, as individual joists have a tendency to roll over easily.

The Can. Institute of Steel Const emphasizes that bridging is not
bracing.
Gary





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