Structural steel design
Steel carries long spans and heavy loads in a slim, predictable frame, which is why it is the material of choice for openings, extensions and commercial structures. We design steelwork to the Eurocodes for clients across the UK, with calculations and drawings your fabricator and Building Control can work from.
What grade of steel do you specify?
For most work we use S355, and S275 where its lower strength is enough. The choice affects member size and cost, so we check both when weight matters, such as a heavy beam that has to be craned or manhandled into place.
Why steel, and how it is graded
Steel gives a high strength for its weight and behaves in a way engineers can predict closely, so it lets you span further and load heavier than timber or concrete for the same depth of member. Most UK structural steel is hot-rolled to grade S275 or S355, where the number is the yield strength in newtons per square millimetre. S355 is now the common default because the extra strength often lets you drop a serial size and save weight and cost. Sections come as universal beams and columns, parallel flange channels, angles, hollow sections and flats, each with published properties for area, second moment of area and section modulus.
The material is close to isotropic, meaning it behaves the same in tension and compression, which makes it efficient in bending and in tied or braced arrangements. It is also ductile, so it yields and warns before it fails rather than snapping without notice. That ductility is what lets us use plastic design in some frames and rely on connections to redistribute load. The trade-off is that steel is slender, so buckling and stability, not raw strength, often govern the design of columns and unrestrained beams.
Designing to BS EN 1993
Steel structures are designed to BS EN 1993, Eurocode 3, with the UK National Annex. The core checks are cross-section resistance in bending, shear and axial load, then member buckling, which covers lateral torsional buckling of beams and flexural buckling of columns. We classify each section from Class 1 to Class 4 to decide whether it can reach its full plastic capacity or whether local buckling of a slender flange or web limits it first. Deflection is checked at the serviceability limit state, typically span over 360 for beams supporting brittle finishes, so floors feel solid and plaster does not crack.
Connections are as important as the members. A beam is only as good as the way it is fixed at each end, so we design bolted and welded connections, base plates, fin plates, end plates and splices to carry the calculated forces and to match the assumed restraint. We specify grade 8.8 bolts, weld sizes and the padstones or stiffeners needed where a heavy point load lands. The output is a set of calculations, a general arrangement and connection details that a fabricator can take straight to the workshop.
Fire, corrosion and durability
Steel loses strength as it heats, so exposed structural steel usually needs fire protection to reach the required period of resistance under Approved Document B. We advise on intumescent coatings, boarding or, where the member runs cool enough, leaving it unprotected on the basis of a section factor calculation. The fire strategy is coordinated with the architect early because it affects the look of exposed steel and the depth of any encasement.
Corrosion is the other long-term issue. In dry, heated interiors bare steel is stable, but anything exposed to weather, condensation or the ground needs a protective system, from a simple paint specification to hot-dip galvanising or a full coating scheme to BS EN ISO 12944 for the expected environment. For work near the coast or in industrial atmospheres we raise the specification to suit. We set out the protection so the steel reaches its design life without ongoing surprises.
What we check.
The points our calculations resolve for a project like this.
- Grade selection between S275 and S355 to balance weight and cost
- Section classification and lateral torsional buckling of unrestrained beams
- Column buckling and effective length for the bracing provided
- Bolted and welded connection design, base plates and stiffeners
- Fire protection period and section factor under Approved Document B
- Corrosion protection specification to suit the exposure
Issued drawings, redacted.
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
What grade of steel do you specify?
For most work we use S355, and S275 where its lower strength is enough. The choice affects member size and cost, so we check both when weight matters, such as a heavy beam that has to be craned or manhandled into place.
Do steel beams always need fire protection?
Not always. It depends on the required fire resistance period and the section factor of the member. A stocky column may run cool enough to be left bare, while a slender exposed beam usually needs intumescent coating or encasement. We confirm this against Approved Document B.
Can you design the connections as well as the beams?
Yes. We design the end plates, fin plates, base plates, splices and bolt groups to carry the forces we calculate, and issue connection details your fabricator can work from. Sizing a beam without designing its ends leaves the most important part undone.
Do you work outside Scotland?
Yes. We prepare steel calculations and drawings for clients across England, Wales, Northern Ireland and Scotland, and for projects in Europe. Desktop design and reports are delivered anywhere, and any site visit is arranged by region.
Tell us what you are building.
Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
Start a project