Wired Science

Getting Structures to Inspect Themselves

Every man-made structure can fail. And when we're talking about something like a bridge or an airplane, the results can be catastrophic - like the I-35 bridge that collapsed in Minnesota last August.

Because bridges are inspected at regular intervals, that sort of structural failure is extremely rare. But what if they were smart enough to monitor themselves and sound a warning before they were stressed through their limits?

It may be possible, thanks to a technology called "structural health monitoring", which involves placing sensors inside a structure that can communicate its vital signs to inspectors.

A rigid structure grows weaker every time it flexes or stretches. Each time a vehicle passes over a bridge, the structure vibrates, straining some parts.  When this stress cycle weakens a structure beyond its endurance limit, the result is one of the biggest threats to the structural health of planes and bridges: metal fatigue.

Visual inspections can spot fatigue after a bridge passes its endurance limit. But permanent sensors can monitor the amount of stress before the structure reaches that limit. That frees up inspecting agencies' limited resources to focus only on the bridges that actually need attention. A wireless system built by a company called Microstrain lets civil engineers monitor bridges via the Internet, using technology originally developed for smart knee implants.

Sandia National Laboratories is developing similar technology to keep tabs on aircraft. That could be a boost for passenger safety, as well as the airline industry's bottom line, as taking a plane out of service for inspection costs them $100,000 a day.

Engineers see a day when such sensors will be hidden in everything from trains and trucks to ships and buildings - tiny sentinels working around the clock to prevent disasters.