Cementitious Deck 2

[I-beam]

I am analyzing roof framing for snow load capacity on a building constructed in the early 1970s.
Roof is constructed with bar joists at 5'oc, spanning to steel beams. The original design drawings
indicate a built-up roof on 1" rigid insulation, over a 3" cementituous deck. Does anyone have
any info on what a cementitious deck weighs ?

Many thanks

 

[hokie66]

"Cementitious' is not very descriptive. Concrete is cementitious, and that would be about 37 PSF. More likely gypsum deck on bulb tees or a fibrous deck such as Tectum or Insulrock on bulb tees. Those decks would be a lot lighter than concrete.

 

[Ron]

Based on the roofing material description you gave, it is likely a Tectum deck. You don't install rigid insulation over a "poured" deck such as lightweight insulating concrete or gypsum when newly placed.

Go take a look at it. Tectum will show a random, curly pattern on the underside. Poured gypsum will show a smooth drywall-like finish from the formboard with steel runners 24 inches apart (the bottom of a bulb tee). Lightweight insulating concrete will show a corrugated metal deck.

In any case, the unit weight of the decking will be between about 6 and 10 psf.

 

[JedClampett]

I found this in my travels.
Philosophical discussion: In the 60's and 70's these were state of the art. Now, I never run into them. Is it an economic thing? Metal deck is just better (it was better then, too)? The labor that knew how to do this retired and wasn't replaced? Poor promotion?

 

[dik]

You need to weigh a 'sample' to get a weight with any confidence. Also, if you know the gauge of the deck you may be able to get the design loading from load tables. Is the deck 'dimpled' on the side of the flutes so it can act compositely? Gypsum or Tectum decks were not commen in these environs during that time.

Dik