Key takeaways
- Composite deck (about 50 mm rib) works with shear studs and concrete to act as a composite slab, often replacing mesh reinforcement.
- Deep rib deck (60–75 mm and above) carries load by itself and is used for longer spans or where propping is undesirable.
- Embossing is what creates the mechanical bond on composite deck — without it the composite design assumption is invalid.
- Both run on the same machine with different cassettes, so profile choice does not force a different machine.
Two different structural ideas
Composite deck is designed to work with the concrete, not on its own. Embossed ribs grip the concrete mechanically, and shear studs welded through the deck tie the steel beam to the slab so the two act as a single composite section. In many designs that composite action removes the need for mesh reinforcement.
Deep rib deck takes the opposite approach: the deeper rib gives the steel enough stiffness to carry the construction load by itself, so it can span further between beams and is often used without composite action at all.
Both are permanent formwork, because in both cases the deck stays in place and becomes part of the finished floor.
| Criterion | Composite deck | Deep rib deck |
|---|---|---|
| Rib height | ≈ 50 mm | 60 – 75 mm+ (re-entrant variants 50–60 mm) |
| Typical span | 2.5 – 3.6 m | 3.6 – 6.0 m |
| Structural action | Composite with concrete via shear studs | Often independent of the concrete |
| Embossing | Essential for the mechanical bond | Not always required |
| Mesh reinforcement | Frequently omitted | Typically still required |
| Propping | Usually not needed at normal spans | Rarely needed even at long spans |
Why embossing matters on composite deck
The composite design assumes the concrete and the steel act together. That assumption depends on the interface between them being able to transfer longitudinal shear, and the embossing pattern is what provides it.
If the embossing rolls are worn or set too light, the deck looks correct but behaves as plain formwork. The composite design assumption then no longer holds, and the slab is under-strength in a way that is invisible on site. This is why embossing roll condition is worth checking on every production run, not just at commissioning.
Which to choose
The answer almost always comes from the structural engineer's span table. If the required span is within composite deck's range at the available slab depth, composite deck is normally cheaper because the mesh can often be omitted.
Deep rib deck becomes the answer when spans exceed about 3.6 m, when the overall floor depth has to be minimised, or when propping the slab during construction is impractical — for example on a site with no access below the floor being poured.
Span and propping decide it before anything else
Work back from the span and the propping requirement rather than from the profile names. If the floor spans 2.5–3.6 m between beams, composite deck is the conventional answer and it usually needs no propping at normal spans: the deck carries the wet concrete, and the finished slab then acts compositely with the beams through the shear studs.
Once the span moves into the 3.6–6.0 m bracket, the unpropped construction stage is what governs. That is where the deeper rib section earns its place — it has the stiffness to carry the wet concrete without temporary support, and it does so largely independently of what the concrete does afterwards.
The trap is choosing on the finished-floor argument alone. Both decks end up as a finished floor; the difference is what happens during the pour, and that is a construction-stage decision rather than a service-stage one.