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

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On Thu, 8 Feb 1996 EDLStruct(--nospam--at) wrote:

> I have a 8" cmu bldg.  It's dimensions are 112' x 70' x 14.5' high.  There
> are steel girders
> 40" deep across the short direction on the pilasters @ 18' o.c..  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.  It probably was built by the Airforce.  It was
> well built.  But there is no drawings.   There is a poured in place concrete
> bond beam at the roof level all around the building.
> my questions are;
> 1 Can anyone who are familia with this type of roof construction tell me more
> in detail?
>    I can not break the roof to investigate.
> 2  I would like to find out how it act as a diaphragm from the detail answer
> of the    question #1.

We have something like this on one of our buildings, which was built 
around that era. If the roof leaks, the Gypsum gets wet and softens. 
There is some mesh in it, but I don't think the mesh is attached to the 
inverted T's as in the other reply. The original roof design did not seem 
to count it as a diaphragm (as well it shouldn't be), since there is 
diagonal bracing in the roof plane. We just recently added more bracing 
up there to get it up to current code. Nobody here knows anything about 
its load carrying capacity, so we attach mechanical equipment to the main 
members. It's OK for walking on if you don't hit a soft spot.

.    .    .   .   .  .  .  .  . . . . . ...........................
Bob Shilling, SE             Berkeley, CA          shilling(--nospam--at)
KK6QQ          MSA Single 10, 3 floor, 4 knee             DoD# 1195
      "This alligator walks into a bar and ..."   Horizon Kent