Metal Decking Calculator — Profile, Studs & Concrete Topping

Composite metal decking is a profiled steel sheet (0.9-1.2mm thick) that acts as permanent formwork for in-situ concrete floor slabs. The deck profile has embossments that create a mechanical bond with the concrete, forming a composite slab that acts as a single structural element. It eliminates the need for traditional timber formwork and propping.

The concrete cover above the top of the deck rib equals the total slab depth minus the deck profile depth — for example, a 130mm slab on a 60mm deck gives 70mm of cover above the ribs. BS EN 1994-1-1 §9.2.1 sets a minimum overall slab depth of 80mm (90mm where the slab acts compositely), with at least 40mm of concrete above the ribs (50mm composite). In practice 50–60mm of cover is typical for fire resistance and crack control. Typical total slab depths are 130mm for a 60mm deck and 150mm for an 80mm deck.

Shear studs (headed studs, typically 19mm diameter × 100mm long) are welded through the deck to the steel beam flange. They transfer horizontal shear between the concrete slab and the steel beam, creating composite action. This significantly increases the beam's load-carrying capacity and stiffness compared to a non-composite beam. Studs are placed in the deck troughs (one or two per trough — TR60+/ComFlor 60 troughs are at about 333mm centres), so the spacing is dictated by trough pitch and by the structural design, not by load alone. The final stud number and layout must be set by the structural engineer to BS EN 1994-1-1; the count this calculator gives is an indicative estimate.

Propping is needed when the beam span exceeds the deck's unpropped spanning capability. For TR60 deck at 0.9mm gauge, the maximum unpropped span is about 3.6m; for TR80, about 4.2m. Propping consists of temporary Acrow props supporting the deck until the concrete has cured to at least 75% of its design strength (typically 7 days).

Anti-crack mesh (typically A142 or A193) is placed in the top of the slab to control shrinkage cracking. Per BS EN 1994-1-1 §9.8.1 the cross-sectional area of this reinforcement must be at least 0.2% of the concrete area above the ribs for unpropped construction, rising to 0.4% for propped construction. A142 (6mm bars at 200mm centres, per BS 4483) is a typical default for office and commercial floors; A193 (7mm at 200mm) or A252 (8mm at 200mm) is used for propped construction, heavier loads or longer spans. The mesh should have at least 20mm cover to the top surface. This calculator sizes the mesh sheet quantity only — confirm the bar area against the §9.8.1 percentage for your slab depth and propping arrangement.