×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Existing Poured Gypcrete Roof Deck

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 would try to run some steel angles across the sides of the openings - welding them to any existing roof joists or members. This would shore up the edges of the openings and allow you to place a new metal deck infill (or plate if it works) over the angles as well.

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.

Check out Eng-Tips Forum's Policies here:
FAQ731-376: Eng-Tips.com Forum Policies

RE: Existing Poured Gypcrete Roof Deck

Do you plan to have the plate over a bulb tee or other structural member so the gypsum is only in compression? Take a look at your loads. Assume you have a big drift and 180 psf total load on a 4' span. The reactions are 360 plf or 30 pounds per inch. Assume you have 3" of bearing. Then, the compressive force is 10 psi.

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

Agree with JAE...frame all penetrations. My rule of thumb is anything 12" or over needs framing.

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

(OP)
Thank you everyone for the quick replies. There currently is supplemental angle framing that is picking up the edge of openings that they want to just leave in place. So my only concern really was the bearing on that existing poured gyp deck. WannabeSE thank you for the pdf for the gyp deck I will have to add that to the library.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources