CIVIL ENGINEERING & CONSTRUCTION
Professor Ken Grattan of City University discusses the advantages of fi bre-optic sensors, which can remotely and precisely monitor the structural health of bridges, viaducts and rail buildings.
M
aintaining the buildings and struc- tures that make up the physical ele-
ments of our rail network is a big challenge, with Network Rail alone having in the re- gion of 40,000 bridges and tunnels in its portfolio.
Anything that could make monitoring those assets for corrosion and structural integrity a little easier is worth investigating, hence the company’s interest in ongoing research by Professor Ken Grattan of City Universi- ty, who specialises in both engineering and physics and has literally written the book on optical fi bre sensor technology.
He told RTM: “We’ve been working with civil engineers for about the last ten years or so, undertaking a number of assess- ments of corrosion damage and strain on various types of bridges around the world. So this project forms a part of ongoing work in that area.
“Our main interest is helping civil engineers to use new technologies to create better sen- sory and measurement systems, and in par- ticular our expertise lies in the fi eld of fi bre optics and fi bre optic sensors. So what we’ve been doing is working with civil engineers so that we can then fi t fi bre optic sensors to a number of structures, and in that way then make measurements on those structures. And following the measurements, what we’re able to do is to work again with the civil engineers to try to assess the nature of the responses that they’ve got. Then, based on that, we try to help them to make suit- able civil engineering focused decisions on
38 | rail technology magazine Aug/Sep 11
how you go forward in the fi eld and we let the civil engineers decide what it means in terms of whether the structure is serviceable or not and how we deal with that.”
New and old
The long-term goals of the project are var- ied, Professor Grattan told us – both to make it easier to monitor more effectively large numbers of structures, and to eventu- ally use the data gathered to help develop better building techniques to boost struc- tures’ integrity and corrosion resistance – and actively build high-tech monitoring sensors into the fabric of the structures.
He explained: “We recognise two things from the work we’ve done over a number of years; one is the retrofi tting of sensors to structures like bridges, and by doing that we’ve been able to monitor better some of the structures that already exist.
“Then secondly, we’ve been able to look, in some cases, at working with the engineers to build sensors into new structures as they are being built – which enables a civil engi- neering structure to have a sensor system built into it, and so to have a capability then for ongoing monitoring.”
Under pressure Making improvements
Structures on the rail network obviously experience stresses and pressures of kinds not seen outside of a transport context.
Professor Grattan said: “There are certain-
We asked Professor Grattan to assess the relative impact of speed and load on struc- tures like bridges, and their effect on struc- tural integrity.
ly stresses associated with these structures being used on a day-to-day basis over many decades. A very good example is that we’ve just come back from India, where we’ve been doing work with the Indian Institute of Technology in Bombay to monitor a con- crete bridge on the commuter rail network coming in to Bombay.
“They have a bridge, a 1980s bridge, which is subject to cracking; the bridge has now developed a number of cracks. What we were doing with them was doing some very specifi c tests – we had the bridge closed off overnight, we had a heavy locomotive of known weight per axle, driving at a known speed over a particular point. We fi tted up our fi bre optic sensors, and there were some conventional sensors on the bridge as well.
“We were able to monitor the strains on the bridge, and we’re looking at some new fi bre optic techniques to monitor how cracks will gradually open as a result of the loading that’s applied to a bridge. So what you can do is monitor the changes in cracking. Ob- viously there comes a point where you can decide whether you put a weight limit on the bridge, or do you stop people using the bridge even, and so on. That Indian bridge is a very good example of just some of our interesting work that’s been ongoing.”
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