CIVIL ENGINEERING & CONSTRUCTION
He explained: “Load is more important. As you change speed, you get a different dy- namic load on the bridge, and that clearly is important. But certainly, total load is an issue and it seems to be the case that what’s been happening to bridges is that they have been affected in that way. You can apply weight restrictions if you’re beginning to be concerned that they’re suffering damage.
“This work is all a way to try to make things better, as far as the bridges are concerned, and really give the owners of the bridges the confidence that they can continue to be used – or indeed, sometimes, to have to say the opposite: to say there’s a problem.
“With our British work, we have had inter- est from Network Rail, which obviously has concern for bridges and structures in the UK and therefore, they have an obli- gation to make sure that those are fit for purposes. So from that point of view, we’re very happy to work with as important a group as Network Rail, so that we can get a very clear picture of what their needs are and then try to respond to that, through the work we do.”
Technological solution A different example of the potential for
what that wavelength change is.
fibre-optic sensors is Professor Grattan’s work
investigating dewirement, which
sparked interest from around the globe when covered on Rail Technology Maga- zine’s website – including queries from rail workers from Zimbabwe, SNCF in France, and from Invensys Rail in Thailand.
Professor Grattan explained more about the varying uses of fibre optic sensors – an interest of his ever since his PhD in the mid 1970s, with his research into using laser- probe techniques for measurements.
He said: “What we’re looking at is so-called fibre Bragg grating type sensors. Basically, it is a sensor where you write a grating into an optical fibre, and then as a result of the changes that you want to measure, whether it’s physical change as a result of say strain or temperature (or indeed you can config- ure them for chemical changes by applying certain coatings) then you can get a meas- urement which results in a change in wave- length and you can measure dynamically
“So, the big advantage is that you can put a network of these sensors on a very large structure like a bridge. Even if you’ve got a bridge hundreds of metres in length with lots of sensors, then you can connect them together into a network, and that distance between the sensors doesn’t matter.
“It’s more difficult, for example, using con- ventional sensors like conventional strain gauges: if you have lot of those on a bridge (and we did have on the bridge test that we were doing in Bombay) then you get lots and lots of cables, because of the individual connections that have to be made between the sensor and the interrogation box.
“You can end up with a forest of wires that come from the series of conventional devic- es. Also conventional devices are very deli- cate, while the fibre optic sensors can cer- tainly be made very robust and very much fit for purpose.”
Visit
www.tinyurl.com/4xn348p Ken Grattan
FOR MORE INFORMATION
rail technology magazine Aug/Sep 11 | 39
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