Reinforced concrete design
Reinforced concrete pairs concrete that is strong in compression with steel bars that carry the tension, giving a material that can be shaped into slabs, beams, columns and foundations. We design and detail reinforced concrete to the Eurocodes for clients across the UK.
What concrete strength do I need?
It depends on the loads and the exposure. A heated interior slab might use C25/30, while a foundation in aggressive ground or a heavily loaded column may need C32/40 or higher for both strength and durability. We specify the class alongside the cover so the structure lasts its design life.
How reinforced concrete works
Concrete is strong in compression but weak and brittle in tension, so on its own it cracks and fails wherever a member is bent or pulled. Reinforced concrete solves this by casting steel reinforcing bars into the tension zones, where the bars take the tension and the concrete takes the compression, and the two act together because they bond and because they expand at almost the same rate with temperature. Getting the bars in the right place, at the right cover and lapped correctly, is the heart of good concrete design.
Concrete is specified by strength class, such as C25/30 or C32/40, where the numbers are the cylinder and cube strengths in newtons per square millimetre. Higher classes give more strength and better durability but cost more and generate more heat as they cure. Reinforcement is normally grade B500B ribbed bar. The mix, the cover and the class are chosen together to suit both the loads and the exposure, because a beam in a heated interior and a foundation in wet ground need very different specifications even at the same load.
Designing to BS EN 1992
Concrete structures are designed to BS EN 1992, Eurocode 2, with the UK National Annex. We check bending, shear and, for columns, combined axial load and moment at the ultimate limit state, then crack width and deflection at the serviceability limit state. Deflection is often the control on slabs, and Eurocode 2 handles it through span to depth ratios or an explicit calculation, so floors do not sag or feel lively. Shear is checked to see whether the concrete alone is enough or whether links, the vertical bars that stop diagonal cracking, are needed.
Detailing is where concrete design succeeds or fails. We set the bar sizes, spacing, lap lengths, anchorage and cover so the reinforcement can develop its full strength and so the concrete stays durable. Minimum and maximum steel areas, curtailment of bars where the moment drops, and links to hold the cage together are all set out on bar bending schedules and detail drawings the steel fixer can follow. A slab that is under-detailed at the supports will crack there regardless of how much steel sits at mid-span.
Durability, cover and construction
Concrete protects its reinforcement by keeping it in an alkaline environment, so durability is mostly about giving the bars enough cover of sound, dense concrete for the exposure class. Eurocode 2 sets exposure classes from dry interiors through to chloride-laden coastal and de-iced conditions, and each drives a minimum cover and often a minimum concrete class. Too little cover lets carbonation or chlorides reach the steel, which then corrodes and spalls the surface. We set the cover and class to give the structure its intended life without early repair.
The design also has to be buildable. We consider how the concrete will be poured, how the reinforcement is craned and fixed, where construction joints fall and how the formwork is struck, because a detail that cannot be poured or vibrated properly will not perform as calculated. For foundations we suit the design to the ground, whether that is a simple pad or strip, a raft over soft or variable ground, or pile caps tying a piled solution together.
What we check.
The points our calculations resolve for a project like this.
- Concrete strength class and reinforcement grade to suit loads and exposure
- Bending, shear and deflection checks to BS EN 1992
- Crack width control at the serviceability limit state
- Bar detailing, lap lengths, anchorage and cover for durability
- Column design under combined axial load and moment
- Foundation type suited to the ground, from pad and raft to pile caps
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 concrete strength do I need?
It depends on the loads and the exposure. A heated interior slab might use C25/30, while a foundation in aggressive ground or a heavily loaded column may need C32/40 or higher for both strength and durability. We specify the class alongside the cover so the structure lasts its design life.
Why does cover to the reinforcement matter so much?
The cover of concrete over the bars protects them from corrosion and gives fire resistance. Too little cover lets carbonation or chlorides reach the steel, which rusts and cracks the surface off. Eurocode 2 ties the minimum cover to the exposure class, and we set it accordingly.
Do you provide bar bending schedules?
Yes. We issue reinforcement detail drawings and bar bending schedules to BS 8666 so the steel fixer knows every bar size, shape, length and position. The detailing is as important as the member sizing, especially at supports where cracking usually starts.
Can you design concrete foundations and rafts?
Yes. We design pad, strip and raft foundations and pile caps in reinforced concrete, suited to the ground conditions and the loads coming down from the frame. For projects across the UK we work from the available ground information and advise where an investigation is needed.
Tell us what you are building.
Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
Start a project