Old Gypsum Roof Board
Old Gypsum Roof Board
(OP)
I'm trying to determine load capacity for the roof of an indutrial builing that's sheathed with 2" thick gypsum board (no metal or wood decking - just this 2" + 1/2" gyp board ceiling on steel joists). It does not appear to be of the Densdeck or Securerock variety - there's no visible reinforcing fibers in the gypsum, the paper is not visibly reinforced. There is a layer of thin wire mesh (like chicken wire) about 1 1/4" down. The building could be 30 years old. Anybody seen this stuff &/or know how to evaluate it for point loads?






RE: Old Gypsum Roof Board
RE: Old Gypsum Roof Board
RE: Old Gypsum Roof Board
This was a common deck type in the 1950's, 1960's and even into the 1970's, for commercial and industrial applications.
A variation on this that came about in the late '60's, early 70's was the use of fiberglass insulation formboard on the bottom, instead of the gyp board.
Design info is hard to come by. Generally the gypsum material had a compressive strength ranging from about 500 to 1500 psi. The spans are short (2 feet), so distributed loads were not a big deal. Point loads should be checked as punching shear, since bending is likely not going to prevail.
RE: Old Gypsum Roof Board
http://nrdca.org/webfiles/NRDCA%20500.pdf
http://nrdca.org/webfiles/GypsumRepairPictures.pdf
Here is an article that would be nice to get, but I can't find it anywhere online:
http://cedb.asce.org/cgi/WWWdisplay.cgi?14415
RE: Old Gypsum Roof Board
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A lot of good info in those thresads!
My joists are 6' oc with the builb tees about 3' oc. At this point i am feeling pretty leery about adding significant load to this stuff & will figure out a solution that loads directy above the joists.
RE: Old Gypsum Roof Board
RE: Old Gypsum Roof Board
How are the new angle members connected to the roof? I know that there the the bulb tees, but what about the opening perpendicular to that?
RE: Old Gypsum Roof Board
Span the bulb tees with angle sufficient to carry the load spaced 18 inches apart. So you have two parallel angles, spanning 24 inches with an 18 inch space between them. Now span two more angles perpendicular to the first two, spanning the 18 inches between the first two angles, and spaced 18 inches apart. You now have an 18 inch square frame supported by the bulb tees.
RE: Old Gypsum Roof Board
My project requires a change of occupancy which changes the Importance Value from 1.0 to 1.15.
My major concern is how can I calculate the capacity of the gypsum when it really isn't attached to the "bulb tee"?
What prevents the gyp from being completely pulled free from the bulb tee?
Any ideas for engineering a system to transfer this load?
RE: Old Gypsum Roof Board