Designers using more steel in buildings than necessary

The construction industry is using almost double the amount of steel in buildings than is required by safety codes, which is having a dramatic impact on carbon emissions, latest research has revealed.

Researchers at the University of Cambridge analysed 10,000 structural steel beams in 23 buildings across the UK and found that, on average, they were only carrying half the load they were designed for. The results were published in the journal Proceedings of the Royal Society A and funded by the UK’s Engineering and Physical Science Research Council.

Buildings covered by the study were “typical” UK steel-framed buildings constructed within the last five years, mainly schools, offices and residential buildings. The study estimates that if the design of the 23 buildings was optimised to include only the required amount of the material to meet safety standards it would save 1,027 tonnes of steel. When scaled up to apply to the 290 million tonnes of steel used worldwide to construct buildings each year this would save 106 million tonnes of steel annually, averting 214 million tonnes of CO2 emissions.

“The problem is structural engineers do not usually design fully optimised structures because it would take too much time, instead they use repetition to decrease the cost of construction,” said Dr Julian Allwood of the department of engineering at Cambridge, who led the research. “This leads to the specification of larger steel components than are required.”

Over a quarter of the steel produced each year is used in the construction of buildings and demand is increasing rapidly, especially in the developing world where usage is expected to double in the coming decades, the report states.

Dr Allford claims structural engineers tend to look at the heavily loaded areas of the building and design carefully there, but in less heavily loaded areas the design is copied and pasted from standard specifications because they know it will be safe and cheaper than going through a detailed specification and calculation process.

This trade off between paying for more steel and less design labour can have a major impact on costs, he said: “Structural steel might cost £600-£700 a tonne, whereas employing a design engineer could cost the same per day, so using less design labour and more steel could work out cheaper. Ultimately it depends on the client and their will to get things designed in an optimal way rather than the method they are accustomed to.”

The report recommends two methods for reducing the amount of rationalisation in construction: increasing the time engineers have to design buildings, or increasing use of steelwork design and optimisation software. “Both strategies involve extra cost, but the reductions in steel mass could offset these, particularly as weight savings compound, in other words, a lighter floor-structure requires less column material to support it and thus smaller foundations, particularly for tall buildings,” the report states.

Dr Allford heads up one of six government-funded centres of national research into energy demand reduction, and is currently seeking industry partners to carry out a more in-depth examination of the labour/steel trade off on a specific project, which would be monitored to assess costs and determine how a better balance could be struck on projects in future. More information is available on the website www.ukindemand.ac.uk.

The iron and steel industry contributes nearly 10% of total global carbon emissions, which climate change experts recommend should be halved by 2050. “Drastic action is required if a reduction in the sector’s carbon footprint is to be achieved,” the report states.