Aluminium structural design
Aluminium is light, naturally corrosion resistant and easily formed into custom extruded shapes, which makes it the material of choice where weight and weathering matter more than raw stiffness. We design aluminium structures to the Eurocodes for clients across the UK.
Why is aluminium not just a lighter version of steel?
Because it is far more flexible. Aluminium's stiffness is about a third of steel's, so a member of the same shape deflects three times as much. Aluminium design is often controlled by deflection and buckling rather than strength, and members are deepened or stiffened to compensate, so it is not a straight swap.
Aluminium as a structural material
Aluminium weighs about a third of steel for the same volume, and it forms a tight natural oxide film that resists corrosion without paint, so it earns its place where a light, weather-resistant structure is wanted. It is extruded rather than rolled, which means the shape can be tailored to the job, with flanges, grooves and stiffeners drawn into a single custom section, so aluminium members are often more efficient than a standard steel profile for the same purpose. Structural alloys are specified by series, commonly the 6000 series such as 6082 for extrusions and the 5000 series for plate.
The catch is stiffness. Aluminium's modulus of elasticity is about a third that of steel, so an aluminium member deflects three times as much as a steel one of the same shape and load, and buckling is more of a concern. This means aluminium design is very often controlled by deflection and stability rather than strength, and members are made deeper or given extra stiffeners to compensate. Understanding this trade-off, light and non-corroding but flexible, is the key to using aluminium well rather than treating it as a drop-in for steel.
Designing to BS EN 1999
Aluminium structures are designed to BS EN 1999, Eurocode 9, with the UK National Annex, which mirrors the steel code in structure but adds the features aluminium demands. Section classification and local buckling matter more because the thin, complex extruded shapes are prone to it, and we classify sections and allow for it explicitly. Deflection at the serviceability limit state frequently governs given the low modulus, so we check it carefully rather than assuming the strength check is enough. Fatigue is a real consideration where the structure sees repeated loading, since aluminium has no clear fatigue limit.
Welding aluminium changes the metal, and the design has to allow for it. Many structural alloys gain their strength from heat treatment, and welding softens a zone either side of the weld, the heat-affected zone, where the strength drops back towards the annealed value. Eurocode 9 handles this with a reduction over the softened region, so we design connections around it, favouring bolting where it suits or placing welds where the reduced strength is acceptable. We set out the alloy, temper, weld and bolt requirements so a fabricator can produce the structure to the assumptions in the calculations.
Corrosion, contact and where aluminium suits
Aluminium's natural oxide makes it durable in most atmospheres without coating, but it has two weaknesses to detail around. It is attacked by strong alkalis, so direct contact with fresh concrete or mortar needs an isolating coat, and it suffers galvanic corrosion when it touches other metals in a damp environment, so contact with steel or copper is separated with an insulating washer, tape or coating. Where the environment is aggressive, industrial or marine, we specify a suitable alloy and, if needed, anodising or coating to lift the durability further.
Aluminium suits canopies, walkways, rooflights, curtain walling and facade framing, access structures, and anything that has to be light, moved, or left exposed without maintenance, which is why it dominates glazing and cladding support. Its limits are stiffness, cost per kilogram and the softening around welds, so it is rarely the right answer for a heavily loaded primary frame where steel is cheaper and stiffer. We advise where aluminium's low weight and corrosion resistance justify it and where another material serves better, so the choice is made on merit rather than habit.
What we check.
The points our calculations resolve for a project like this.
- Alloy and temper selection such as 6082 extrusions or 5000 series plate
- Deflection and buckling governing design given the low modulus
- Local buckling of thin extruded sections and classification
- Heat-affected zone softening around welds to BS EN 1999
- Fatigue where the structure sees repeated loading
- Galvanic and alkali corrosion, isolation from steel and concrete
From enquiry to sign-off.
Enquiry
Send drawings or describe the problem. We confirm the scope, the deliverables and a target timescale.
Information
We agree the survey, drawings or data we need and any site access required.
Engineering
Design, calculation or assessment to the relevant Eurocodes and UK National Annex.
Issue
A clear, defensible report or set of calculations, with assumptions and limitations stated.
Common questions
Why is aluminium not just a lighter version of steel?
Because it is far more flexible. Aluminium's stiffness is about a third of steel's, so a member of the same shape deflects three times as much. Aluminium design is often controlled by deflection and buckling rather than strength, and members are deepened or stiffened to compensate, so it is not a straight swap.
Does aluminium need corrosion protection?
Usually not in ordinary atmospheres, because its natural oxide film protects it. But it must be isolated from wet concrete, mortar and dissimilar metals such as steel to avoid alkali and galvanic attack, and in marine or industrial settings we may anodise or coat it. We detail the isolation and any coating to suit the exposure.
Can aluminium be welded structurally?
Yes, but welding softens the alloy in a zone around the weld, so the strength there drops. Eurocode 9 accounts for this heat-affected zone with a reduction, and we design connections around it, often favouring bolting or placing welds where the reduced strength is acceptable.
Where does aluminium make sense structurally?
Where light weight and corrosion resistance matter, such as canopies, walkways, rooflights, curtain walling, facade framing and access structures. For heavily loaded primary frames, steel is usually cheaper and stiffer. We advise which suits the project across the UK.
Tell us what you are building.
Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
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