Articles · 2026-09-07 · 5 min read
Half the beam is doing nothing
What 12,787 beams from real UK steel frames say about utilisation, rationalisation and how much steel a code-compliant frame can lose.
In 2014 Cambridge engineers took 23 steel-framed building designs from leading UK practices, 12,787 beams and 2,347 columns, and checked every member against the load it was designed to carry. The average utilisation ratio was 0.40. Weighted by length it rose to 0.48, and by mass to 0.54. The abstract puts it plainly: over 10,000 beams average below 50% of their capacity (Moynihan and Allwood, 2014).
The cause was not error. It was rationalisation: providing extra material to reduce labour costs. One section repeated across a floor is cheaper to detail, fabricate and erect than twelve sections each sized to its span. The steel is a known cost; the coordination it saves is not on the drawing.
How much could come out
The same group later measured the gap between the section drawn and the lightest Eurocode-compliant section for some 3,500 floor beams in 30 UK buildings. Choosing the lightest section alone saved 26.5% of beam steel by mass. With a 3 Hz natural-frequency assumption and average rather than characteristic yield strength, the saving reached 34.5%. About a third of the steel in the frames could have been saved, which the paper puts at 36% of the frame's initial embodied carbon (Drewniok, Campbell and Orr, 2020).
The 2014 study makes a similar estimate from the other direction: lifting average utilisation from 0.54 to a feasible 0.90 with existing section catalogues would cut beam steel by about 36%.
Why the tonnes do not translate one for one
Material is only 30 to 40% of what a steel frame costs. Fabrication is another 30 to 40% and erection 10 to 15%, and non-standard sections push the frame rate up because fabrication costs more (steelconstruction.info, Q3 2025). Taking a quarter of the beam steel out therefore saves nearer a tenth of the frame cost, unless the number of section sizes stays sensible.
That is the honest version of the argument, and it is still a large number: on a 5,000 m² office at 90 kg/m², a quarter of the beam steel is about 72 tonnes. The worked arithmetic is on the examples page.
What to do with a drawing set
- List the section sizes on the framing plan. If five sizes cover most of the floor, ask which spans set them.
- Check the beams governed by deflection or vibration rather than strength; that is where the 26.5% came from.
- Put the fabrication trade-off on the table before the set is issued. After tender, the rationalisation is priced in.