The detail that makes a composite floor composite
A composite floor works because the concrete slab and the steel beam beneath it act together as one structural unit rather than as two separate things stacked up. The component that ties them together is the shear stud, and on most composite floors those studs are welded through the deck onto the beam below. This is through-deck stud welding.
It is easy to overlook because it happens quickly and quietly on site. But without it, you do not have composite action, and without composite action the floor is a different, weaker structure than the one that was designed.
What the studs actually do
The shear studs resist the horizontal sliding force between the slab and the beam. When a composite floor is loaded, the top wants to compress and the bottom wants to stretch, and at the interface between concrete and steel there is a shear force trying to slide one past the other. The studs lock the two together so they resist that force as a single member.
The result is a floor that carries more, deflects less, and often needs less steel than the same beam would if it were acting alone.
Why weld through the deck?
Welding the studs through the deck, rather than to a bare beam before the deck goes down, is what makes the sequence practical. The deck is laid first, giving a safe working platform and permanent formwork for the slab. The studs are then welded down through the deck onto the beam flange, fixing the deck and providing the composite connection in one operation.
What the process needs to do right
Through-deck welding is reliable when the conditions are right, and unreliable when they are not. The essentials are a clean, dry contact between deck, stud and beam flange, correct equipment settings, and welders working to the correct procedure. Damp, dirt, galvanised coating thickness and beam flange thickness all matter, which is why it is work for trained, certified operatives rather than something to improvise on site.
At RMD our teams are NVQ Level 2 qualified for decking and stud welding, so the connection is done properly and tested as it should be.
The bearing detail people miss on through-deck stud welding
Here is the practical point worth carrying away, and it links to something we go on about elsewhere: bearing.
The minimum end bearing for a deck sheet on steel is 50mm. But where the deck is to receive through-deck welded shear studs, that increases to 60mm. The extra bearing gives the stud the seating and edge distance it needs at the sheet end for a sound weld.
That 60mm is not a site decision. It has to be designed in against the steelwork drawings before the sheets are cut, because a sheet cut short cannot be stretched. It is exactly the kind of small detail that is free to sort on a drawing and expensive to discover on a part-laid deck.
For the full picture on bearing, see our guide on why deck bearing matters.
Where RMD comes in with through-deck stud welding
We supply and fix composite floor decking with through-deck stud welding as part of the package, and our drawing office checks the bearing and stud details against your steelwork before anything is manufactured. Send us your structural GA drawings and we will make sure the detail is right from the start. RMD Profiles are expert composite floor construction UK based.
Learn more about our floor decking services, or send your drawings for a quote.
Telephone 01787 275055. Email sales@rmdp.co.uk. If you want more information on our product services, click here. Composite flooring construction UK experts.