Gypsum roof deck on cardboard 1

[sbouvia]

I was wondering if anyone has seen this roof deck system before. It appears to be gypsum poured over cardboard which spans between steel joists and wide flanges beams. At some locations the wires in the cardboard appear to be spanning over the beams/joists, however for most of the structure the wires in the cardboard are in same direction as beams/joists. Any help would be greatly appreciated.

Thanks,

Scott

 

[briancpotter]

How old is this building, and where was it built?

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[sbouvia]

1950's to 1960's and Washington, DC

 

[lexpatrie]

Oh, dear.

No, thank you.

Generally this system involves a gypsum board and a bulb Tee. That's the one I'm familiar with seeing "in the field." Those have wire but it is up in the poured, not underneath.

I'd ask the fire chief out to see if he wants that in his jurisdiction before I did anything with it. Looks like it might not support the 250 lb point load.

If you are still curious, have the roof cut into from above. You might be able to find reinforcement in the poured gyp, but given the five or so foot span, those systems more commonly span two feet. I believe the board used in the poured (and wire reinforced) gypsum is considered largely a form, so the cardboard might just be a form. Anyway, given the difference in conventional span and what you have here, I wonder if there isn't something else going on besides what you can see.

 

[bmrossetti]

This looks like one of the United States Gypsum cast in place roof systems. As lexpatrie indicated, there is often a steel section embedded in the gypsum. The wires parallel to the joist span appear to be bent up at the perforations in the cardbaord, and are presumably draped over the steel sections at those locations.

I've attached a US Gypsum document for their gypsum roof systems c. 1980 to give you an idea of the details; however since this document is 20-30 years more recent than your building take with a big grain of salt.

Are you modifying the roof or increasing the loads? If not, probably best to let it be ;-)

Hope this helps,

Brandon

 

[JAE]

This article appears to discuss this system.

http://www.block.arch.ethz.ch/sites/research_group/files/pdf/publications/suco_201100014.pdf

Look at items 3 and 4 on page 165.

 

[sbouvia]

Bmroseetti sounds like a name I know


It is the roof of a fourth floor addition of a building, which appears to have no lateral resistance in the North-South direction except for at one point in time interior 4" masonry wall butting up tight to WF column webs. It appears that after the events that took place on August 23, 2011 the masonry no longer provides lateral resistance as the mortar between the webs and the interior walls is gone leaving a 1 to 1.5" gap, therefore the building appears to be moving during wind events.


We are eventually going to do a lateral analysis of this building and are trying to determine if this roof is flexible or rigid, or somewhere in between.

It does appear to be some sort of gypsum material, and I think it looks like a metropolitan slab construction, however I am not sure if they continued that construction into the 60's. Also as typical in some existing building we have no existing documents. I am thinking we will be doing a probe at the roof over the top of one of the beams in order to determine if it is the typical gypsum system with Bulb tees.

Thanks for all of the help guys.

 

[bmrossetti]

Yes, I think this is who you think it is... how is everything going? You the last man standing yet, or what? ;-)

Sounds like an interesting project. A probe is probably your best move at this point. I would not be surprised if instead of steel section (such as bulb tees) there is only welded wire mesh acting as a draped mesh between the joists, with the the "secondary" wires parallel to the joists serving to reinforce the cardboard/fabric form during construction phase (which would explain why the secondary wires run below the cardboard instead of within the gypcrete) and distribute the loads in service conditions.

Let me know how it goes.

Brandon