Composite Steel Decking: How It Works and How to Specify It
How composite steel floor decking works: profiled galvanized deck, concrete slab, shear studs, propping, spans, fire rating and what to specify when buying metal deck.
Saudi Steel Work Editorial Team · · 3 min read
Short answer: Composite decking is a profiled galvanized steel sheet laid on steel beams that acts as permanent formwork while concrete is poured, then bonds with the hardened slab to act as tensile reinforcement. Shear studs welded through the deck make the beams and slab act together, increasing strength and stiffness.
Composite floors are the standard floor system for steel-framed buildings, car parks and mezzanines. They combine steel beams, profiled steel deck and a concrete slab into one efficient structure.
The components
- Steel beams — usually IPE, UB or W-sections
- Profiled steel deck — galvanized sheet, typically 0.75–1.2 mm
- Shear connectors — headed studs welded through the deck to the beam
- Concrete slab — with mesh and any additional reinforcement
How it works
During construction: the deck spans between beams and supports wet concrete, construction loads and workers — acting as permanent formwork.
In service: embossments in the deck profile bond with the concrete, so the deck acts as bottom reinforcement. Shear studs make the beam and slab act compositely, so the slab works as a wide compression flange. The result is a stiffer, stronger floor with lighter beams.
Re-entrant vs trapezoidal profiles
| Profile | Features |
|---|---|
| Re-entrant (dovetail) | Flat soffit, easy hanging of services, good fire performance |
| Trapezoidal | Longer unpropped spans, less concrete volume |
Propping
Each deck profile and gauge has a maximum unpropped span. Beyond it, temporary props are needed during the pour. Designing within unpropped limits saves time.
Fire resistance
Fire rating depends on slab depth, reinforcement and protection of the beams. Requirements follow the building code and Civil Defense. See fire protection of structural steel.
What to specify
- Deck profile and gauge
- Steel grade and zinc coating (e.g. Z275)
- Lengths per layout drawing
- Edge trims, closures and stud specification
- Through-deck welding requirements
Common mistakes
- Using roof deck where composite floor deck is required
- Ignoring galvanizing thickness for through-deck stud welding
- Leaving out edge trims, causing concrete leakage
Need decking? See our steel decking range or request a quote.