Smarter, safer bridges with Sandia sensors

Monitoring sensors
The structural health monitoring system for the trial bridge consists of eight Comparative Vacuum Monitoring sensors, a vacuum pump to form the vacuum, a control system to turn on the vacuum pump and periodically check the sensors and a wireless transmitting device to autonomously call or text the maintenance engineers if a sensor detects a crack. The whole system is powered by a lithium ion battery, which is recharged by a solar panel.

The sensors were placed along several welds on a truss 100 feet above the deck, or flat road surface, on a suspension bridge.

The Comparative Vacuum Monitoring sensors produced by Structural Monitoring Systems are made of thin, flexible Teflon and have rows of little channels, called galleries. They can be stuck onto critical joints or welds or placed near other places cracks are likely to form. When the metal is whole, the pump is able to remove all of the air out of the galleries, forming a vacuum. When a tiny crack forms in the metal underneath the sensor, it can no longer form a vacuum, similar to how a vacuum cleaner stops working when the hose has a leak. These sensors can detect cracks smaller than the thickness of a dime.

The sensors can be produced in many different shapes, depending on the region that needs to be monitored, such as across a long weld or around a series of bolts. They can even be placed in a series in front of a tiny crack, to see whether it grows and if so, how fast. Each sensor has numerous control galleries and monitoring hardware so it can tell if there’s something wrong with the sensor or connecting tubes. Because of these control galleries, the sensors are practically foolproof.

Henry Kroker, a Structural Monitoring Systems engineer who played a key role in the bridge monitoring project, said, “Comparative Vacuum Monitoring sensors provide an elegant ‘Green-Light, Red-Light’ method for constantly surveying critical components. In many years of trial and permanent use in the aviation and now civil industries, these sensors have not produced any false calls.”

Future of structural health monitoring
Sandia notes that the team’s work on smart infrastructure began in 2005