What is stud welding? What are shear studs? As an experienced Stud Welding contractor, in this knowledge article we take a detailed look at what stud welding is, what shear studs are, what they are used for and the main benefits of using them in composite floor construction.
What is Stud Welding?
Stud welding is the process of welding a shear stud to another metal object. Stud welding is also known as drawn arc stud welding, or arc welding for short.
‘Stud welding’ and ‘shear studs’ are terms often used in connection with steel frame and composite floor construction.
What is the Shear Stud Welding Procedure?
Shear studs are usually applied in situ using a stud welding gun. The stud welding procedure involves heating the end tip of a shear stud (or shear connector) using a strong electric arc created by a positive electric current.
Upon triggering, the studs are held in the welding gun at a pre-set height above the parent material whilst a pilot-arc is struck. This is followed by the main arc which generates heat of over 1400 degrees so that the weld end of the stud starts to become molten and a molten pool forms on the plate. This molten metal is known as welding splatter. The shear stud is then driven at force into the molten pool on the surface of the parent material where the two parts are fused together.
Whilst the duration of each weld process is determined by the type and size of the shear connector, the stud welding process can take as little as 0.06 seconds. On average, a shear stud will be reduced in length by approximately 5mm during the welding process.
What is a Ferrule?
Ceramic ferrules, also known as ceramic arc shields, are protective rings that are utilised in the stud welding process to shield a shear connector and ensure a clean and uncontaminated weld.
Ferrules keep the molten metal pool contained between the stud and the parent material and stop it from spreading outwards. This ensures there is sufficient molten metal to fuse the two materials together and create the strong weld.
Ferrules also shield the shear connectors from the air during the welding process. This reduces the risk of the weld becoming porous or contaminated which could weaken the weld and also reduces UV exposure in the immediate area.
Once the process is complete, the ceramic ferrule is chipped away and discarded.
How Strong is Stud Welding?
Despite the speed at which the process can be undertaken, the resulting connection between the two metals is stronger than either the stud or the parent material itself and is capable of withstanding greater static loads.
Stud welding can be used on parent materials as thin as 1.2mm.
What is Stud Welding Used For?
In the construction industry, and in particular steel frame construction, stud welding techniques are often used to connect shear studs to the top flange of the steel beam.
In some cases, they are pre-welded straight to steel beams. However, it’s more common for the studs to be welded through steel decking sheets. This is known as ‘thru deck welding’.
A concrete slab, reinforced with either steel mesh sheets or steel fibres, is then cast on the steel decking with the concrete encompassing the exposed top of the studs.
Thru deck stud welding should be undertaken as soon as possible after the steel decking has been laid to prevent the build-up of contaminants that may affect the quality of the weld, such as dirt or moisture.
The shear connectors create a strong vertical connection between the steel beam, steel decking and the reinforced concrete floor slab. The shear stud improves the overall composite action and transfers load bearing force between the materials; the horizontal shear is resisted by the shank and vertical uplift is prevented by the head.
Overall, the resulting composite floor slab is capable of carrying heavier static and dynamic loads than each material in isolation whilst still being relatively lightweight.
Composite Floor Design and Stud Welding
When designing composite floors as part of a steel frame structure, structural engineers will refer to load/span tables produced by metal deck manufacturers, such as Kingspan. These load/span tables allow the structural engineer to assess both the thickness of the concrete floor slab and the type of mesh reinforcement required in order to achieve a particular fire rating or construction requirement.
Once the reinforced concrete floor slab has been designed, the structural engineer is able to finalise the design of the composite beam, i.e. the steel beam and the composite floor slab.
Engineers must adhere to proven design standards outlined in Eurocode 3, Design of Steel Structures, and Eurocode 4, Design of Composite Steel and Concrete Structures.
An essential part of the composite beam design process is the design of the shear connectors. The Eurocode design standards provide proven formulas for calculating the volume or force that can be carried by each shear stud. This allows the composite floor designer to determine the number of shear studs required for each beam and how far apart they must be spaced.
What are the Advantages of Stud Welding in Composite Floor Construction?
Stud welding is a fast and efficient method of fusing a metal shear stud to a parent material whilst creating a weld joint that is stronger than either the stud or the parent.
To weld the shear stud, access is required from only one side, meaning the process can be undertaken on site once beams are installed, therefore reducing the need for excessive component handling. Stud welding equipment is also portable and does not hamper the manoeuvrability of the stud welder.
The reverse side of the steel beam is unaffected by the process and the area around the shear connector is usually flat and clean.
As no holes are made in the steel beam, stud weld joints are leakproof. The risk of corrosion is also reduced and the strength of the steel beam is not adversely affected.
What are the important considerations when Stud Welding?
Due to the extreme temperatures associated with the process, stud welding can be a fire hazard so the process must be carried out by a trained operative who will assess conditions in line with health and safety best practice.
The metal splatter generated when the arc is struck between the tip and parent material will shower in all directions above and below the location the stud welding is taking place, as this video shows.
This molten metal will continue to smoulder when disbursed and, if allowed to come into contact with other materials or surfaces and not detected, carries a high risk of a fire outbreak both during and outside of site working hours.
Typical fire prevention methods are ineffective due to the nature of the molten splatter. Fire protective monoflex could reduce risk by minimising the distance the splatter is disbursed; however, it is not a fully preventative method.
There is no safe means of carrying out works if any third-party materials, equipment, buildings or machinery are either below or adjacent to the area of activity. The CDM Regulations 2007 require composite slab designers, such as Raised Floor Solutions, to foresee possible fire risks and to design out a solution at pre-construction stage.
What Are the Alternatives to Stud Welding?
Where fire is an uncontrollable risk, an alternative to ‘hot works’ stud welding should be recommended.
One possible alternative is the application of shot fired fixings (or shot fired shear connectors), such as the Hilti X-HVB.
What Are Shot Fired Fixings?
The Hilti X-HVB is an ‘L’ shaped shear connector that is ‘shot’ along with two nails into a steel beam using a cordless powder-actuated tool, commonly referred to as a stud welding gun.
As with traditional shear studs, the shape of the shear connector has been designed to resist vertical uplift and longitudinal shear force.
The gun is cordless and instead powered by small explosive cartridges, therefore this method of attaching shear connectors to a steel beam also reduces the risk of trip hazards on site.
Stud Welder Services from Raised Floor Solutions
Raised Floor Solutions operates a fleet of bespoke mobile stud welding rigs that are specially designed to enable access to even the most compact construction sites.
All Raised Floor Solutions’ stud welders are fully trained and operate to the highest levels of health and safety, as well as the strict quality and safety standards required by CHAS Premium Plus and Achilles, to which Raised Floor Solutions is accredited.
Metal Decking and Composite Concrete Floors from Raised Floor Solutions
Raised Floor Solutions is the UK’s largest approved supplier and installer of Kingspan Multideck metal decking. Through its specialist steel decking contractor division, Metal deck, it is able to provide clients with a comprehensive composite steel floor decking service that includes stud welding services.
Steel decking supply and installation is complemented by an expert reinforced concrete flooring contractor division, Metcon. Metcon will design and install a reinforced composite concrete floor on steel decking. It can also design and construct concrete ground floor slabs, external concrete floor slabs and concrete floor refurbishment works.
Find out more about steel decking and composite concrete floor slabs in our knowledge article.
To learn more about our expert composite floor contractor services call our team on 01695 555070 or email us.