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Re: metal roof decking

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We have had to do this exercise in  the past per building official requests.
Our conditions were using CMU walls and joists were spaced at 6' on center
(pretty much the same thing).

The deck needed to be analyzed where the joists were parallel to the wall.
The axial load came from the deck supporting the walls against out-of-plane
loading due to seismic/wind loads.  And of course the bending loads were
from gravity.  The gravity load used depended on the snow loads, if any.
The steel deck manufacturer provided the section properties and we just
followed the light gauge steel procedures or cold formed steel design
recommendations for the interaction equations.  So far we have never had to
stiffen the deck.  Overall, this is just another step in the analysis of the

For joists perpendicular to the wall, the axial loads from the wall are
resisted by the joists.  A horizontal bond beam at the diaphragm level spans
horizontally to transfer the loads to the joists.  The deck is parallel to
the wall at this location and has no axial load carrying capacity.

I'm sure there are many other ways to analyze your situation.  I did not go
into much detail for the above analysis, but this should get you pointed in
the right direction.

Mike Brown, P.E.

-----Original Message-----
From: Dave Anderson <dnae(--nospam--at)>
To: seaoc <seaint(--nospam--at)>
Date: Wednesday, September 02, 1998 10:21 PM
Subject: metal roof decking

>Is anyone design 18 gage metal decking as roof diaphragm
>no concrete and to support tilt up wall 34 feet long
>if yes . did you check it for axial and bending loads?
>that in CA . zone 4 ! by 96 UBC revision
>the joist spaced 8 feet on center
>thanks in advance
>D.A. P.E.