Slots in steel decking?

Maybe somebody can refresh my memory. What’s the purpose of the slots in the steel decking?

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Composite Decking for a concrete slab.

What’s the purpose of the slots, Marcel? And why is it called “composite” instead of “steel”.

Composite slabs consist of profiled steel decking with an in-situ reinforced concrete topping. The decking not only acts as permanent formwork to the concrete but also provides sufficient shear bond with the concrete so that, when the concrete has gained strength, the two materials act together compositely. That is why the deformation slots as you call it, come into play.

So the slots act as keyways increasing the shear bond between the concrete and steel?
Also, would you ever expect to see this system used for an intermediate floor, or just roof decking?

Yes, they help reduce slippage (shear) between the steel deck and the concrete slab, which technically is called composite action.

Yes, you could see that used in multi-level commercial buildings.
Roof decking is different, and called B deck. Painted or galvanized.

Here are a few pictures of a building I built using this type of deck.
That job also called for shear studs.

Slots are in the sides of the ribs instead of the bottom, I guess that’s because the shear studs are welded to the bottom.

I’m working on a comprehensive commercial template, but man, I don’t have a background in commercial construction and the libraries are all closed because of Covid. The Engineering Library at the University of Colorado in Boulder isn’t even loaning books to students right now… faculty only. It’s hard to find good online information on commercial and industrial building systems.

There are many different types of composite decks depending on the manufacturer.
This manual here should answer anything you want pertaining to steel decking.
Anything you need to find out on commercial and industrial, I can help if I can.

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Thanks Marcel! Checking out those links now.

This one might be better for you, it shows the deck with the vent tabs. It’s a manufacturer’s catalog.

Got it, thanks!

As @mcyr put it, roof decking is usually painted, powder coated, or galvanized. And it’s smooth. If it had ridges, it could possibly hold moisture in the event of a roof leak. A layer of rigid foam is usually placed atop the decking before roofing membrane is placed.
The ridges in the decking shown in your pictures also add rigidity to the material that helps with flexing when the concrete is poured.
I dealt with both of these styles many times back in my commercial construction days…

This type of composite deck is popular in CA. I have dealt with Steel Deck Institute,, on public school projects that I have inspected. Their information is not free, but it is very informative. Each brand of decking may have different seam locks as well. I have inspected several decks that the seam lock tool was not properly adjusted and the seam punches were not deep enough to provide adequate joint. If not installed correctly, the deck can give way during concrete placement.

Is that something that you can identify visually from below? I though most steel deck panels were connected with welds.

If you look carefully you can see the blistered paint on the bar joist if they used 1/2" puddle welds and Hilti pins if that is what they used. Tek 5 screws are also used at times on bar joists. When installed on beams you might not see anything. You also will see at times, stitch screws at the panel edges, but if crimp punch was used, you might not see anything. Depends on how the deck lap is made. All types of fastening are usually specified in the contract specifications.