UK engineers have found a way to bulldoze the building industry’s emissions of the greenhouse gas CO2. The University of Cambridge’s Muiris Moynihan and Julian Allwood say that better use of steel could halve emissions without any impact on safety. ‘We’re using double the amount of steel that we actually need,’ Julian told me.
Julian is director of UK Indemand, one of six national centres the country’s government set up in 2013 to help reduce energy demand by boosting efficiency. Construction is one of the first areas it’s tackling in its mission to reduce industrial energy and material use, and in turn cut CO2 emissions.
Today builders use lots of steel because ‘the cost of materials is low, and the cost of structural engineers is high’ Julian said. “Rather than designing a building precisely it’s cheaper to focus on the heavily loaded areas of the building and design carefully there. Then you can copy and paste, in effect, that design out to other areas that are less well loaded because you know it’s going to be safe. It’s quicker to do that than to spend the professional time required to design the structure accurately.”
Steel-making has one of the largest carbon footprints of any industry, its factories coming fourth in the list of ‘stationary emitters’ behind electricity generation, cement production and oil refining. Every year over 1.5 billion tonnes of steel are produced, emitting around one-tenth of the CO2 from energy generation and industrial processes worldwide. Julian and his coworkers had previously forecast that steel use will double in the next 37 years. If reducing steel use is possible, it therefore looks an obvious move to help avoid dangerous climate change.
Muiris and Julian therefore looked girder-by-girder at the ‘utilisation ratio’ of 10,130 beams and 1,837 columns in 23 UK buildings mainly offices and schools. “It’s the fraction of the capacity of the beam that is actually required in order to meet safety standards,” Julian explained. “The safety standards have several features in them which include strength, stiffness, vibration, and a few other requirements. They are already very conservative. We compared what had been designed against what was required to meet all of those safety standards.”
If steel beams and columns carry loads exactly equal to the safety standard level then their utilisation ratio would be 1. However, in a paper published in Proceedings of the Royal Society A on Wednesday, Julian and Muiris found that the average ratio across the 23 buildings was 0.54. That means around half of the steel used in them isn’t necessary. On a conservative estimate of raising the ratio to 0.9 in all buildings across the world, the Cambridge engineers projected we can avoid emitting 214 million tonnes of CO2 every year.
That’s a modest saving when laid against the 36 billion tonnes of CO2 emitted by burning fossil fuels in 2013. However UK Indemand emphasises that it will help the building industry meet the four-fifths reduction in emissions demanded by the country’s 2008 Climate Change Act. In a prospectus launched in tandem with the publication of their paper Julian’s centre outlines a strategy for meeting the target that rests on two pillars. One is reducing steel use, and the other is using buildings until the end of their designed life of 100 years, rather than the current average of 40 years.
But will builders buy it? If they use so much steel because it’s the cheapest way to go, can they really be expected to voluntarily change their behaviour? Julian’s quietly confident. “It’s probably a pretty low cost to sort it out, although we don’t know yet and we’re trying to get evidence about it,” he said. “We reckon it’ll be about 1-2% at most of the total project cost in increased labour, against which, of course, there’ll be some saving in reduced material purchasing.”
Moynihan, M., & Allwood, J. (2014). Utilization of structural steel in buildings Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 470 (2168), 20140170-20140170 DOI: 10.1098/rspa.2014.0170