Sensors Mag

Can We Get Smarter Structures Now?

August 10, 2007 By: Melanie Martella, Sensors


E-mail Melanie Martella

Last week a bridge in Minnesota fell down. This week, criminal charges have been filed against Big Dig suppliers who have been implicated in the tunnel ceiling collapse that killed a Massachusetts woman. The part that kills me in all of this is that both events were preventable.

Operating Principles

My needs are simple and few. I expect bridges to stay up, tunnel ceilings to stay ceilings, dams to remain intact, and for the rest of the civil infrastructure to stay still and not crumble. In the case of the ongoing problems with Boston's Big Dig, I accept that in a project of this complexity and magnitude, there will be gremlins. I also accept (human nature being what it is) that some people will get greedy and cut corners. But when the technology exists to monitor structures and give early warnings of problems and the technology isn't used and people die, then I get cranky. For an excellent and spirited overview of Big Dig problems and how sensor technology could have helped, I suggest reading Stephanie Henkel's October 2006 essay "Engineering vs. the Bottom Line".

In the wake of the Minneapolis bridge collapse there's been a great furor over the less than stellar condition of many of our bridges. In fact, the American Road and Transportation Building Association collected a bunch of relevant information for interested journalists on the condition of the highways and bridges. If you want to get a good night's sleep I might advise you not to look at the PDF down at the bottom of the page, summarizing US bridge and highway conditions for 2006. In my own state of New Hampshire some 32% of our public bridges are classified as functionally obsolete or structurally deficient. The fact that we had three hundred-year floods in an 18-month period definitely didn't help.

If the Minneapolis bridge collapse achieved anything good, it was to raise awareness of condition monitoring systems that are designed to spot fatigue cracks and other structural problems early. For instance, Material Technologies and its electrochemical fatigue sensor, LifeSpan Technologies, and Strainstall UK Ltd., to name just three.

All of these technologies involve instrumenting the structures in question, measuring the stresses and strains experienced, and providing some hard data to the people trying to decide whether the structure in question is fine or needs to be fixed or replaced. Sending someone out to eyeball a bridge or perform spot tests periodically can only help so much—having detailed time histories of the condition of a structure seems a lot more effective when judging its health.

Cash and Caution

The fact that the technology exists to measure the relative health of our bridges is only part of the picture. This technology isn't cheap. I don't know about you, but I haven't heard of a single department of public works or state department of transportation that's rolling in cash and I'm willing to bet that systems such as this can be a hard sell. According to the USA Today article "New bridge-monitoring devices go unused," many states have been slow to adopt these new technologies because they aren't sure that the technologies are cost-effective.

I also suspect that it's easier to get funding to replace a broken bridge than it is to fix one that's ailing. I hope, ardently, that the Minneapolis bridge collapse spurs states and municipalities into investing in and using these systems. We've got the technology, we just have to use it.


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