steel floor deck composite requirements

[said the noob]

Hi Guys,

my factored load is about 232 psf (11kpa), for a triple span floor deck that is 38mmx0.91mm thk P3615/P3606 canam deck of spans 1800mm has a capacity of 7.45kpa, now if the slab is considered composite with the beams I have a capacity of 20kpa, I do not need composite action for my supporting beams,

my question is to make this composite I would need to add welded nelson studs to my beams, would I need to check this through a shear flow situation to determine the horizontal shear? I am trying to figure out if I should just up the thickness of the deck, or add nelson studs to make it composite, which would you guys go for a more economical path?

thanks

 

[mmarlow]

Being that you say the beams dont need composite action, I'm having trouble picturing how the deck would need to be composite with the beams? Wouldnt the deck span perpendicular to the beams? In my experience I. familiar with the steel deck being composite with the concrete, and the beams arnt included.

Studs would be added in the case that the steel beams arnt stiff enough or strong enough. But it sounds like your carriers are ok?

I dont see where studs come into play if the beams are sufficient?

I'd go through a steel deck manufacturers span tables and determine how adding the DL of thicker concrete will affect your spans and constructablity. More concrete will mean the unshored constructuon length of the deck will go down. In the case that you cant get your selected deck to work (unshored construction span) with the needed thickness of concrete, I'd go with e heavier deck.

-MMARLOW EIT

 

[CANPRO]

You’re confusing composite deck and composite beams. Nelson studs made the beam composite with the slab and have nothing to do with your composite slab capacity.

To increase your composite slab capacity you can either increase your deck gauge, decrease your beam spacing, or increase your slab thickness. I’d imagine increasing slab thickness is least economical as added weight carries through the design. Watch you don’t exceed your maximum unshored span of the deck.

I usually try to stick with the lightest deck gauge and minimal slab (4”/102mm would be standard) and see if that gives me a decent beam spacing.

If you’re looking at non-composite deck and you need more floor capacity, use the composite deck, the cost difference is minimal.

 

[said the noob]

supporting beams are OK without composite action, I have 90mm topping on top of the deck.

I do not know if the steel deck can be assumed composite if just cast on top of the steel deck with no studs as the steel deck is smooth as seen on site. I tried searching the canam catalogue but cannot find anything on this,but I did find something on the CMC joist and deck catalgue noting that studs are not required for composite slab action, and only required if the beams supporting the deck require the additional capacity,but this is because the decks are made with "rolled-in" embossments that interlock the deck with the topping slab.

the maximum unshored spans for composite slab is 2285mm for triple span so I am OK here,

 

[mmarlow]

CANPRO said what I intended to say, but much clearer.

Studs are not used for composite action between steel deck and slab. Steel decks use ribs for the concrete to bond to.

A "smooth" deck is probably a form deck, not composite.

-MMARLOW EIT

 

[CANPRO]

See page 10 of the PDF linked below. Composite deck gets its composite action through little ribs in the flutes.

https://www.canam-construction.com/wp-content/uploads/2014/12/canam-steel-deck-catalogue-canada.pdf

 

[said the noob]

thank you gents, that is the confirmation I was looking for

cheers!

 

[EngineerEIT]

Studs can help the gravity load carrying capacity of the composite deck. See the below catalog from Vulcraft.

Link

 

[mmarlow]

Structural EIT,

I see the increase in capacity with the studs in the link you attached. Can you explain this? I'm not sure how the studs increase the strength? Unless somehow they contribute to the compaosite action in the deck to concrete?

-MMARLOW EIT