How The Sound Of Rain Helps Engineers Diagnose Unsafe Bridges

Structurally flawed bridges produce a different sound when splashed with water. If we listen in during the rain, we can hear the problem--and fix it--before it gets worse.

Brian Mazzeo and Spencer Guthrie
1210-19 054.CR2 Finding weaknesses in bridges thanks to the acoustic footprint when rain falls. Brian Masseo ECE and Spencer Guthrie CEE Students Jeff Klis and Anjali Patil October 11, 2012 Photography by Mark A. Philbrick Copyright BYU Photo 2012 All Rights Reserved photo@byu.edu (801)422-7322Brigham Young University

To test the safety of a bridge, engineers rely on some pretty low-tech methods. One common way of doing it is to drag a chain across the bridge and listen in for the hollow-sounding spots. But, weirdly, an even-lower-tech method might speed things along: Have the rain do the work for you.

In the same way that structural deficiencies can be detected with something solid, two engineers from Brigham Young University--Brian Mazzeo and Spencer Guthrie--are listening in for the tell-tale acoustics by splashing bridges with water. They're looking for something called "delamination." In a concrete bridge deck, the layers used to build the bridge can become separated over time--it's a major concern with some aging bridges. Right now, some of the processes (like the chain-dragging) can take hours, and shut down lanes for that time.

The water solution is simple, and could potentially fix the traffic problem. One day, the researchers say, it might be as easy as misting a bridge as they cruise by in a car. (No, you don't have to wait for it to actually rain. Although that's more poetic than car-misting.) It might also make its way into related industries, like aircraft construction, where delamination of composite parts is a problem.