Technology has advanced to the point where the condition of bridges, tunnels and buildings can be monitored in unprecedented detail. Now a new Centre at Cambridge has been formed to kick-start the smart infrastructure revolution.
"London Underground needs to know if the Northern Line is good for another 20 years, or another 80, or longer. At the moment, nobody really knows."
—Professor Robert Mair
London Bridge, so far as we know, is not falling down. Whether we would be able to tell if it was about to, however, is a different question. And, if it was, we would need to calculate how much time it had left, so that we could establish when to deny people and traffic access for their own safety. Such matters have been preoccupying researchers like Professors Robert Mair and Kenichi Soga for most of their careers – and with good reason.
Next to many icons of British infrastructure, London Bridge (39 years old in its present incarnation) is a mere spring chicken. Every day, millions of us use bridges, tunnels and pipelines constructed in the Victorian age. Our cities and towns are densely populated networks of infrastructure, much of it a century old or more. They are shaped by the clash of political and public expectations, but they are also home to some of the most important listed buildings, structures and heritage sites in the world. Given the scale of the job involved in ensuring that Britain’s infrastructure remains standing, it seems both astonishing and oddly reassuring that most of it does.
Horror stories about what could happen if it all went wrong sometimes crop up in the news. In 2007, the I-35W Mississippi River Bridge near Minneapolis fell down during the evening rush hour. Thirteen people were killed and more than 100 were injured. This tragedy, it later emerged, was a direct result of the fact that those responsible for maintaining the bridge simply did not know enough about its condition to predict and prevent the collapse.
Yet such ignorance is fast becoming a thing of the past. Thanks to rapid advances in technologies like wireless sensors and fibre optics, it is now possible to keep both old and new infrastructure under constant surveillance, monitoring strain, temperature, displacement, humidity or even a crack in a wall. Researchers believe we are on the verge of developing ‘smart infrastructure’, which will allow buildings, tunnels, bridges, sea defences, or road and railway cuttings to be subjected to regular health checks at the touch of a button.
Mair and Soga, both Professors of Civil Engineering at Cambridge, are among a group of academics at the University making that vision a reality. Last year, an Innovation Knowledge Centre (IKC) for Smart Infrastructure and Construction was set up, based in the Department of Engineering, but involving colleagues from across the University – in the Department of Architecture, the Computer Laboratory and Judge Business School. The IKC works with construction, infrastructure and technology firms. Its aim is ambitious: its founders believe that it could kick-start a new industry dedicated to smart infrastructure and construction in the UK.
“The analogy I use when describing our IKC is that of a car,” Mair said. “A modern car has sensors that can tell you such things as when the brake lights have failed, or the fan belt is broken. Smart monitoring can give us equivalent information about buildings, bridges and tunnels as well.”
In spite of their huge potential, the latest sensor technologies are not routinely used in infrastructure at the moment. The Forth Road Bridge, where corrosion in the main cables has been monitored since 2003, is a rare exception. Mair and Soga believe that we have barely begun to exploit the potential of the latest technologies; little is done to monitor how most bridges are performing and there is virtually no such monitoring of buildings.
Alongside the priority of public safety, there is a strong business case for constantly scrutinising infrastructure. Worldwide, its maintenance costs billions of dollars every year. Even a small percentage improvement in efficiency would engender major savings. “London Underground needs to know if the Northern Line is good for another 20 years, or another 80, or longer,” Mair said. “At the moment, nobody really knows.”
Sensors and optical fibres
One of the aims of the IKC is to develop a new generation of wireless sensors to the point of marketability by 2016. These small devices measure a structure’s physical conditions, such as temperature, vibration and strain. They are ideal for monitoring those parts of infrastructure that cannot be reached with ease, like inside a tunnel or under a suspension bridge.
The Cambridge Engineering Department has already conducted trials with such technology, including one that monitored humidity in the anchorage chambers of the Humber Bridge, where the steel anchor cables have to remain relatively dry to avoid corrosion. Wireless sensors have also been installed to monitor a tunnel on the London Underground, where they measure changes in inclination and cracks.
With wired sensors now a thing of the past, the ‘Holy Grail’, as Mair puts it, is removing the need for batteries. At the moment, the sensors need to have their batteries replaced. One of the IKC’s projects will look instead at using micro-electrical mechanical systems (MEMS), in which miniature devices and circuitry can be etched on to a silicon chip as part of the sensor. Potentially, a very small turbine could be included to harness the wind power produced by passing trains in the tunnel, making the system entirely self-sufficient. On bridges, similar technology could utilise the vibrations from vehicles.
Optical-fibre monitoring, another key research focus for the IKC, has similarly huge potential. Recently, when a new tunnel was built beneath the century-old Thameslink tunnel in London, Cambridge engineers installed optical fibres around the inside of the old brick tunnel. These produced continuous measurement of the changing strains and temperature at every single point along the fibre. Previously, engineers would have had to use conventional survey techniques to analyse the impact of the new tunnel. Now, optical fibres can be used to measure strain directly and continuously – usually at a cost of just 10 pence a metre.
In 1994, Mair headed the geotechnical group examining the impact of London’s Jubilee Line Extension on the stability of that greatest of British landmarks, Big Ben. Then, huge amounts of meticulous manual measurement went into assessing whether the clock tower was under threat. When boring begins for the huge Crossrail project underneath London this year, he and his team will again be analysing the impact on other buildings, but this time also with fibre optics and sensors. “The technology we have now offers a whole new dimension compared to what was available for the Jubilee Line Extension,” he reflected.
In new structures, incorporating optical fibres during the construction process itself would enable an unprecedented level of ‘cradle to grave’ analysis of how stable our infrastructure is. At the moment, considerable over-estimation goes into the use of many components in buildings and structures to guarantee safety. Better monitoring would allow construction firms to make far more accurate judgements about how much material to use. With technology also enabling the off-site manufacture of building components, it should be easier for these firms to insert sensors and optical fibres into walls, facades and beams, by adding them to components in the factory before they reach the building site – thereby creating the ‘smart’ building.
The IKC has been funded to the tune of £17 million, £10 million from the Engineering and Physical Sciences Research Council and the Technology Strategy Board, and the rest from industry collaborators. By 2016, Mair and Soga hope that the Centre will have advanced both the technology and business cases sufficiently to be able to support its future through industry collaboration alone.
If all goes to plan, Britain could by then be well on its way to becoming a centre for smart infrastructure and construction on a global scale. Work is already taking place with partners in the USA, China, Hong Kong and Japan, parts of the world where monitoring infrastructure is vital given the greater threat of earthquakes and other natural disasters. Mair and Soga have already used optical fibres successfully in a project on the Singapore metro. “The infrastructure of some of these countries is in a state of very fast growth,” Soga added. “Like us, they are starting to realise that smart monitoring could have huge benefits.”
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