US engineers pinpoint flaws in bridges by analysing rain noise

Engineers in the US have found a way of identifying structural flaws in bridges by analysing the sound they make in the rain.

A team from Brigham Young University has adapted a method called impact echo testing to study the noise of raindrops striking a concrete road bridge to detect delamination (the separation of structural layers).

The engineers found that this was a more efficient and cost-effective way of finding flaws than the traditional, more time-consuming method of analysing the sound of chains being dragged over the bridge and identifying spots where a hollow, dull noise is produced.

‘There is a difference between water hitting intact structures and water hitting flawed structures,’ said Brian Mazzeo, assistant professor in the electrical and computer engineering department and one of the lead researchers on the project.

‘We can detect things you can’t see with a visual inspection; things happening within the bridge itself… The response gives you an indication of both the size and the depth of the flaw.’

Using chains to produce the sound of testing can take hours to complete for a single bridge and requires lane closures, but analysing rain sound can be done much more quickly.

‘The infrastructure in the US is ageing, and there’s a lot of work that needs to be done,’ said fellow research lead and assistant professor in civil and environmental engineering Spencer Guthrie.

‘We need to be able to rapidly assess bridge decks so we can understand the extent of deterioration and apply the right treatment at the right time.’

The researchers hope their study, published in the October issue of Non-Destructive Testing and Evaluation International, could help transform deck surveys into rapid, automated and cost-efficient exercises that could one day take just a few moments.

‘We would love to be able to drive over a bridge at 25mph or 30mph [40km/h or 48km/h], spray it with water while we’re driving and be able to detect all the structural flaws on the bridge,’ said Mazzeo.

He added that the method could also be used to test materials beyond bridges, including aircraft composites, which are susceptible to delamination. ‘We think there is a huge opportunity but we need to keep improving on the physics.’