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Re: [SEAOC] seeking knowledge about precast gypsum or pour-in-place gypsum roof system

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My reply to this query:

>I have a 8" cmu bldg. ..  There are
>12" deep steel joists @ 48" o.c. supported by the steel deep girders.
>For roof construction, there seem to be small upside down steel Tee's @ 36"
>o.c. sitting on the steel joists.  There are light brown shiny paper sitting
>in between the Tee's.   On top of the paper is gypsum MAY BE about 2.5"
>thick.  I don't know whether it is poured in place or prefabbed.  There MAY
>BE a solid insulation board about 2" thick on top of the gypsum.   The
>roofing skin is 3 or 5 ply roofing with small gravels.
>It was built around 1960. ....>1 Can anyone who are familia with this type
of roof construction tell me more>in detail?

>Ed Latthitham S.E.
>Ventura, CA

Except for the use of gypsum, it sounds like a popular deck system used when
I started my career in the late fifties. That was in Alberta, but I believe
it was an American product known as "Steeltex".

We used to use it to span directly between open web steel joists, but I
think some people used sub-purlins as you describe. The product was welded
wire fabric with a heavy paper backing. The paper was wired to the mesh
every so often so it could act as a form for a thin concrete slab.

When the concrete was poured on top, the paper sagged below the mesh so the
mesh became embedded in the concrete. Of course, the wire fabric had to be
tied well to the end joists so it could act as a suspension system until the
concrete cured. If the joists at the end didn't pull over (as happened on
one of my jobs), it worked well and resulted in a complete, thin, reinforced
concrete slab that took lots of load. It just looked ugly from below.

If that's the system, it would probably serve well as a diaphragm. However,
I don't know what the difference would be for gypsum concrete. 

Good luck. I always wondered what ever happened to the Steeltex system.

Jim Warne
James Warne Consulting Engineer
Vancouver, Canada