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in situ reinforced concrete floor slab

Reinforced Concrete Floors – An Expert Guide

As experienced concrete floor contractors, our Metcon Concrete Floors division are concrete floor specialists able to design high-performance concrete ground floors or suspended concrete floors on composite steel decking. In this knowledge article, we’ll explain what is a reinforced concrete floor, what is mesh reinforcement, and discuss in detail composite floor construction and composite slab design.

What are reinforced concrete floors?

Reinforced concrete floors are a type of formwork found in the construction industry.  They comprise sheets of steel mesh laid horizontally on a sub-structure around which concrete is cast to form a ground floor slab, or suspended floor slab.

Concrete can also be reinforced with steel fibres which are added to the concrete mix before it is poured.

What is steel mesh reinforcement?

Steel mesh reinforcement is an important element of concrete floor slab design and construction.

Reinforcing steel bars (also known as rebar) are cut and laid in a grid format before being welded to form mesh sheets. Concrete floor contractors use large quantities of these steel mesh sheets in the construction of reinforced concrete floors. The sheets are laid horizontally on a sub-structure. Concrete is pumped on top of the steel mesh reinforcement and allowed to dry hard so the mesh becomes embedded within the concrete floor slab.

In the construction of suspended floors, such as on steel frame buildings, the sub-structure is often composite metal decking

Steel mesh reinforcement is available in different grades which vary from A142 (6mm rebar) to A393 (10mm rebar). The grade of steel mesh used is dependent on the performance and spanning capabilities of the composite metal decking profile specified and the thickness of the concrete floor slab.  Mesh grade thickness also takes into account any additional loose steel bar reinforcement required to support concentrated loads on the floor slab design.

Sheets of steel mesh reinforcement are most often supported on concrete mesh spacers which ensure the mesh stays in position during the casting of the concrete floor slab.  The steel mesh reinforcement should be positioned so it sits within 15mm to 40mm from the top of the finished concrete floor slab.

What is fibre reinforced concrete?

Fibre reinforced concrete is an alternative to steel mesh reinforcement in concrete floor construction.  Steel fibres are added to the concrete mix before it is pumped onto the sub-structure and the concrete floor is cast.

In composite floor construction, steel fibre reinforcement can replace mesh reinforcement when certain profiles of composite metal deck have been specified. When Kingspan Multideck steel decking has been specified, steel fibre reinforced concrete can be used with profiles MD50-V3, MD60-V2 or MD80-V2.

Steel fibre reinforced concrete can be prepared off site to a specified dosage. It can also be used for the construction of concrete hardstandings and heavy-duty industrial concrete floors.

There are many advantages to using steel fibre as concrete floor reinforcement:

  • Eliminates the requirement for mesh hoisting and placing
  • Reduces labour time and, therefore, cuts programme times (on some projects by as much as two days per concrete pour)
  • Particularly beneficial on high-rise structures and sites in confined areas, or on sites with limited space for material storage
  • Performance of the concrete is greatly improved with better shrinkage control and reduced cracking
  • Provides a consistent level of reinforcement across the whole of the concrete floor structure

Why do concrete floors need reinforcement?

Concrete as a construction material is strong in compression but weak in tension. Unless reinforced, concrete subjected to high traffic, heavy loads and even extreme temperature changes can crack, bend, become brittle and structurally unsound.

The benefits of reinforced concrete flooring

By adding a method of reinforcement to a concrete floor it is possible to improve its durability, strength, fire and load bearing performance and longevity.

Reinforcement will:

  • Help control cracking within the concrete floor slab (some cracking is inevitable)
  • Allow the even distribution of pressure from loads applied to the concrete slab (tensile stress is transferred to the steel rebar)
  • Improve the resistance of the concrete floor to fire (steel and concrete react to changes in temperature in the same way, therefore reducing internal stresses)
  • Enable a thinner concrete floor slab to be constructed

Mesh reinforcement v’s steel fibre reinforcement

Steel fibre reinforced concrete has the added benefit of being quicker to install than mesh reinforcement, and there is no requirement to store the rebar on site or to hoist it to the required storey for installation.

Steel fibres will typically provide an even distribution of reinforcement throughout the entire concrete slab which improves its flexural strength and crack resistance and provides the surface of the concrete with higher impact resistance. 

As neither mesh nor fibre reinforcement can prevent cracks from occurring in a concrete slab, properly spaced control joints should be incorporated into the concrete floor slab.  Should a crack occur where it was not expected, steel mesh reinforcement will do a better job than fibre reinforcement of containing the crack and preventing it from opening up further.

Why is steel used for concrete floor reinforcement?

Steel is durable and relatively lightweight; it also has excellent tensile strength whereas concrete has compressive strength.

Steel reacts to thermal changes in the same way as concrete. This means internal stress, or damage, to the concrete floor slab is avoided as both steel and concrete expand and contract as temperatures increase or reduce.

When used together in composite concrete floor construction, the two materials complement each other’s weaknesses and greatly improve the structural rigidity and load bearing capabilities of the concrete floor.

What is composite concrete floor construction?

Composite concrete floors are a method of formwork frequently used in construction, particularly on steel frame buildings.

Reinforced concrete is cast in situ on sheets of profiled composite steel decking (also known as composite metal decking). Together the steel and concrete combine to create a composite floor slab (also known as a composite slab) which is more durable and has a better fire and load bearing performance than each material has if used in isolation.

Illustration of a Concrete slab with metal decking profile
A Reinforced Concrete Floor Example Showing Steel Mesh Reinforcement

Also within the composite floor slab are shear studs which are welded through the composite steel deck to the top flange of the steel beam before the steel mesh reinforcement is laid and the concrete floor slab is cast.

A specialist stud welder from raised floor solutions at work on a steel decking contract
A Stud Welder at Work Installing Shear Studs on Metal Decking

The advantages of composite construction

Composite construction has many advantages:

  • It has exceptional load bearing capabilities
  • It is a lightweight method of formwork resulting in
    • reduced foundation requirements
    • reduced programme schedules
    • reduced programme costs

What buildings use composite construction?

The structural efficiency and cost efficiency of composite construction make it an extremely popular choice of formwork for all types of buildings:

  • Industrial Buildings (such as warehouses, factories and Amazon distribution centres)
  • Multi-storey buildings such as car parks, office blocks, residential apartments, student accommodation scheme, hospitals and leisure centres
  • Buildings with just one storey, such as a raised deck car park or smaller scale school or residential apartment scheme

Composite floor construction in industrial buildings

Composite metal deck and reinforced concrete floors are often used in the construction of industrial buildings to provide concrete external hardstandings, internal concrete floors and internal mezzanine floors capable of withstanding heavy static and dynamic loads.

Composite floor construction for multi-storey car parks

composite car park decking used for the construction of Luton Airport Multi Storey Car park

Composite floor systems deliver many benefits to those involved in raised deck and multi-storey car park construction:

  • Provides large unpropped span widths reducing the need for multiple columns beneath the floor levels
  • Allows flexibility in design therefore maximising the potential number of car parking bays provided, and maximising car park revenues
  • A time and cost-efficient method of construction, particularly raised deck car parks which in some cases can be erected in just a few days
  • In most cases, it allows neighbouring buildings, such as a shopping centre, hospital or railway station, to remain operational during construction
  • Capable of withstanding large static and dynamic loads
  • Reinforced concrete floors are a durable and long-lasting method of formwork

What is composite slab design?

Composite slabs should be designed by a qualified engineer to provide accurate fire and load calculations, concrete reinforcement, slab thickness and to, therefore, ensure a building’s structural integrity.

Reinforced concrete floor design, including designing concrete floors on steel decking, is a service offered by concrete floor contractors, Metcon.

Metcon Concrete Floor Contractors

Metcon is a dedicated concrete floor contractor division within Raised Floor Solutions that specialises in the design and construction of reinforced concrete floors.

Concrete floors can be designed and installed on steel decking and reinforced with either steel mesh or steel fibres.  Metcon will also design and construct reinforced concrete ground floor slabs and install perimeter edge shutters, progressive collapse details and in situ concrete structural screed toppings to precast concrete.

In partnership with sister division, Metal Deck steel decking, Metcon will provide a complete composite flooring construction service using Kingspan Multideck steel decking. A specialist metal roof contractor division, Metalroof, will also supply and install structural metal roof deck.

Contact the Metcon concrete floor contractor team to discuss your next construction project.