What Is Composite Floor Deck?

Composite Deck Concrete Slab Design

What is Composite Deck?

A composite steel deck serves several key functions. It safely supports the weight of wet concrete over a span, it’s own weight or dead load and the construction activity. Once the concrete has cured the composite steel deck embossments, concrete, rebar and slab design engage together to form a composite section to resist the loads applied to the concrete slab.

Composite Deck FAQs:

What is Composite Deck Used For?

O’Donnell Metal Deck composite deck or often referred to as floor deck is used in a variety of applications. Floor decking for concrete is typically used for floors in commercial buildings, bridges, slab infills, porches, parking garages and self-storage facilities.

How Far Can Composite Decking Span?

Every project has unique design criteria as determine by the EOR (engineer of record) and the EOR is responsible for specifying the composite deck that will meet this design criteria. There are two main structural functions to be considered for the design of composite decks. First, the composite deck as a form to support construction loads and second, the composite slab design for superimposed floor loads after the concrete hardens.

What Are The Dimensions Of Composite Deck?

Metal composite deck is made by rolling steel coil into various shapes called profiles. Thus, there are different types of roof decking that have unique dimensions and thus properties. The different metal composite deck profiles allow specifying engineers to design for specific requirements.

How Wide is Composite Deck?

The width of composite floor deck generally accounts for the overlap that is required and is often referred to as cover width. Generally speaking composite decking cover width is available in either a 36" or 24" cover width.

Types of Composite Floor Deck

Composite decks are distinguished by the presence of embossments. Embossments are regularly spaced indentations on the surface of the deck profile for obtaining a composite action between the metal deck and the poured concrete slab. These embossments found only on and are unique to composite deck are used to interlock concrete and steel together.

From an engineering perspective the embossments act as shear connector devices as part of the deck. They are designed to mechanically lock the concrete and deck together so that the concrete and the deck work together to carry subsequent floor loads specified.

What Gauge is Composite Deck?

The metal deck gauge is a unit of measurement that refers to the thickness of the steel.  The higher the gauge number the thinner the steel. The lower the gauge number the thicker or heavier the steel is.

Example 1:

20ga 9/16 form deck is thicker, and therefore stronger & heavier than 26ga 9/16 form deck

Example 2:

22ga 9/16 deck is thinner, and therefore lighter & weaker than 20ga 9/16 form deck

Steel Deck Thickness Chart

What Gauge Composite Deck Do I Need?

The (EOR) or Engineer of Record should be dictating the composite deck gauge requirement for the specific job requirements. However, typically the composite deck gauge will depends on the below factors:

  1. Load capacities and/Concrete slab capacities
  2. Span capabilities of the deck during or after construction
  3. Diaphragm shear values

Below is a chart of thicknesses measured in inches for commonly used gauges for steel composite decking.

Most Common Composite Deck Gauges

Type Gauge Thickness / (in.") (lbs. / ft2)
1.5 Composite 16 (ga) .0598 3.35
18 (ga) .0474 2.65
20 (ga) .0358 2.05
22 (ga) .0295 1.65

Type Gauge Thickness / (in.") (lbs. / ft2)
2.0 Composite  16 (ga) .0598 3.28
18 (ga) .0474 2.52
20 (ga) .0358 1.90
22 (ga) .0295 1.64

Type Gauge Thickness / (in.") (lbs. / ft2)
3.0 Composite 16 (ga) .0598 3.57
18 (ga) .0474 2.85
20 (ga) .0358 2.15
22 (ga) .0295 1.78


Types of Composite Deck Finishes

The finish of the material used for steel deck is most commonly one of the below:

Galvanized deck exposed to ordinary atmospheric conditions does not need to be field painted for structural purposes. Often times, painting galvanized deck is desired for aesthetic purposes. It’s important to note that proper steps are taken to ensure proper adhesion to galvanized coils if a primer is not applied at the factory. Various oils or chemicals used to prolong the life of the coil may impact paints ability to adhere properly.

Phosphatized Painted composite floor deck – is an uncoated steel top sometimes referred to as Phos-painted.  "Phos-painted" is a rare finish specification . This steel deck finish refers to floor deck which the top is left bare or non-galvanized and the bottom is prime painted. The top of the deck will be phosphatized black steel. The design intent is to allow the concrete to bond directly to phosphatized steel surface.

Since bonding action is necessary for composite decks, paint cannot be on the top surface.

Composite Deck Function Finish Comment
Composite steel floor deck dry interior and non-corrosive The finish of the composite steel deck shall be as specified by the designer and be suitable for the environment of the structure

Since the composite deck is the positive bending reinforcement for the slab it must be designed for the life of the structure

The finish of a non-composite form deck shall be as specified by the designer and be suitable for the environment of the structure
In areas where salt water, either brought into the structure by cars in winter or carried by the wind in coastal areas may deteriorate the deck A minimum of G-90 coating is recommended and the exposed bottom surface of the deck should be protected with a durable paint. The protective measures must be maintained for the life of the building.