Existing Poured Gypcrete Roof Deck
Existing Poured Gypcrete Roof Deck
(OP)
I am working on this building from around 1960 and it has an existing poured gypcrete roof deck system that spans to bulb tees that span to the steel structure. The client wants to close a bunch of existing roof penerations that had existing duck work with a steel plate bearing on the existing deck. Does anyone know what the allowable bearing capacity would be that could act on the existing roof deck? My concern is they want to close like 4 foot square openings with a steel plate. The loads acting on the plate are dead load, snow and some areas of high snow drift. I just don't want the plate crushing the existing roof deck????






RE: Existing Poured Gypcrete Roof Deck
I'm always suspicious of these old gypsum decks - especially near edges of old openings as those are areas that typically leak - so the gypsum could be mush.
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RE: Existing Poured Gypcrete Roof Deck
Typical gyp board has 300-400 psi compressive strength. Or look at the specification at the end of this document: GA-300-73_Gyp_Roof_Decks.pdf. It list the compressive strength as 500 or 1000 psi.
I have only seen a few of these installation (exposed in mechanical penthouses) and they looked good without any signs of water damage. If there is water damage, more may need to be done than fill holes.
RE: Existing Poured Gypcrete Roof Deck
Gyp deck on bulb tees is a special character. See if you can find some of the older literature on it. Some used gypsum formboard and some used fiberglass formboard.
RE: Existing Poured Gypcrete Roof Deck